Thursday, August 12, 2021

An Old Project: The Snakebite Extruder

There's recent interest in the forums on different ways to drive the filament through the hot-end, especially as it seems that the teeth in some gear driven extruders result in artifacts visible in the surface of the prints. 

Here's an example of the problem:

The wood-grain looking waviness in the print surface seems to be coming from the gear teeth in the extruder.

There's an interesting thread on the subject at the Duet3D forums here.

Here's one designer's idea about a different way to drive the filament. 

Here's a recent design that looks very interesting- similar to the one above:

Both of those extruders rely on rolling threads into the filament to drive it through the hot-end. I explored that concept in a crude way several years ago.

Back in 2014, 1.75 mm filament was a new thing, and extruder jams were everyone's biggest problem in 3D printing. I thought that what was needed was a very strong push-force extruder that would be able to force filament through the hot-end and nozzle under almost any circumstances, including a partial blockage of the nozzle.

My new design came about when I found myself a little bored at a makerspace meeting and and started fooling around with a piece of filament and a 6-32 nut I found on the table where I was sitting. I noticed that the nut could be threaded onto the 3 mm filament. That got me thinking that I could use that idea in an extruder to drive the filament by spinning the nut with the motor. 

One problem with that idea was that the nut fit tightly on the filament and caused the filament to twist when the nut was turning. I needed something to prevent the filament from twisting. I decided to add a second nut, rotating in the opposite direction, figuring that if one nut twists the filament, the second one will untwist it. The second nut would have to have the opposite (left-hand) threads. Hmmm.

I did a little research and found that one can buy left-hand threaded 6-32 taps very cheaply (about $7 IRIC), so I ordered one and used it to make a left hand threaded 6-32 nut from a small piece of mild steel.

The next problem was the gears to drive the two nuts. A little shopping found sets of plastic gears for about $2 at American Science and Surplus that would do the job. I added some 5mm diameter brass tubing, and some small bearings to fit the tubing and it was almost done.

Total invested funds- about $30, most of which went to the Budaschnozzle hot-end that, believe it or not, was considered one of the more reliable designs available at the time. I can't say enough bad things about that hot-end but that's not what this post is about, so I'll just leave it alone.

The final final snakebite extruder, assembled. The green printed part is 3 pieces, all indexed to each other to ensure proper alignment when they are assembled. The red and blue gears are just press fit onto 5mm brass tubing and there are bearings at both ends of both pieces of tubing.

Did it work? Yes and no. It was fine at driving the filament, but retraction proved problematic. If the threads in the two nuts didn't match exactly and/or the hole diameters were a little different, one nut experienced more friction with the filament than the other. It wasn't enough to allow the filament to twist but it interfered with retraction. Also, the nuts had fixed diameter, and in those days, filament diameter was poorly controlled, so it would occasionally run into a blob on the filament that wouldn't fit through the nuts.

I thought about using threaded collets that would allow adjustment to fit different filament diameters, or even spring loaded collets to allow automatic adjustment, but ultimately abandoned the project when 1.75 mm filament became the standard to allow higher speed printing. 

The first prototype of the snakebite extruder. I went from this to the "final" design in about a week. The nuts are soldered to the ends of the brass tubes running through the two gears on the sides of the extruder. The mechanical force tended to push the two side gears apart, so I redesigned the top cover to help hold them together.

Here is an intermediate version assembled with the hot-end for print testing. I eventually used smaller gears to drive the nuts. With this 1:1 gearing, a full rotation of the motor drove the filament about 0.8 mm, so with 16:1 ustepping and a 200 step/rev motor, it was about 4031 usteps/mm. The result was slow but very smooth extrusion.

Here is the very first test print made using the snakebite extruder. You can see that there were some retraction problems (and ringing which is not the problem that started this post).

The top of the extruder, with smaller filament drive gears, opened so you can see the gears and bearings. The green part is actually two pieces that fit tightly together to capture the bearings.

Comparison of an early version to the final, size-reduced version.

The three printed pieces of the extruder assembled.

Side view of the final extruder showing how the gears mesh. The large green gear was press fit onto the motor shaft and was able to fit through the hole in the printed base of the extruder.

A print made using the snakebite extruder. It had excellent surface quality except for the random loop-blebs scattered over it.

A close-up of the blebs. I suspect it was part of the retraction problem.

Here are some videos I made of tests of the snakebite extruder:

Monday, August 2, 2021

More Bike Stuff

I've been riding the Priority Continuum Onyx (PCO) daily for about 4 months now (see my post here) and have made a few changes for comfort and convenience. I've also, finally, had to do some maintenance/repairs. I had a flat tire on the rear wheel, and the front brake developed a horrible squeal. 

The flat tire repair wasn't hard, but getting the shifter cables off the rear wheel proved to be a little difficult. However, once they were off, the repair went as any flat tire repairs does, and putting the wheel back on the bike and reattaching the shift cables was no problem.

The brake squeal was fixed by cleaning the brake disc and pads with disc brake cleaner followed by scuffing them with sand paper and a wipe with IPA. A total of about 15 minutes was all it took.

Other than those two minor issues, the bike has performed flawlessly. Shifting is always instantaneous and silent, the generator that powers the head and tail lights keeps humming right along. 

I list the stuff I added/removed from the bike, below:

Safety gear

I finally replaced my 20+ year old Giro helmet with what I have found to be a much more comfortable Specialized Echelon II helmet in flat black to match the bike. Back in the Giro helmet days, helmets came with a bunch of different thickness foam pads to adjust the fit. Now they have a single thin layer of foam and a knob on the back of the helmet that you turn and you can feel the helmet hugging your head as it tightens up.

Specialized Echelon II helmet. Very comfortable and the matte black finish matches the Priority Continuum Onyx bike.

I like to ride in the evening because it's usually cooler, less windy, less traffic, and I won't get sunburned. Staying alive when riding at night requires being seen. To that end I am using a set of Cygolite Hotrod lights that are small, light, rechargeable, and bright, to supplement the PCO's built in head and tail lights. I put the white light on the left side of the fork and the red light on the back of the bike's rack. Their batteries are good for more than a week of my riding between charges.

Cygolite Hot Rod lights mount on the bike using stretchy rubber straps. I put the white one on the left side of the fork and the red one on the back of the rack on my bike. The straps are secure and seem to hold up in exposure to weather. The lights are rainproof, too.

I need my hands to work, so I bought some gloves to protect them in case I fall, and they are reflective so my hands will be quite visible at night when signaling turns, etc. They aren't great cycling gloves- not much padding for my palms, and they have seams between the thumb and forefinger that make using the twist shifter uncomfortable, so when they wear out I'll replace them with proper cycling gloves.

Reflective glove lit by the flash in my phone. Normally just looks gray with a little color. The colors you see depend on the angle you view them from.

I bought a 247 Viz reflective vest to ensure that I'd be seen at night. This thing is very bright and easy to fold up and carry in my bike bag. It will fit over my coat in winter.

I added reflective tape to the wheels, helmet, and rack, and may add even more.  You can never have too many reflectors on a bike!

I added a Hafny bar-end rear view mirror so I can more easily see if someone is approaching from the rear. The mirror is made of polished stainless steel, so should be more scratch resistant than polycarbonate mirrors, and it won't break if the bike falls over or I crash (though the mount may break). The mount seems well designed and easy to install and adjust. The mirror is convex and gives a wide angle view of things approaching from behind, but the optical quality isn't as good as a glass or polycarbonate mirror. 


While I was waiting for the PCO to arrive after I ordered it in January, I also ordered a Deploy bag from Timbuk2 that was offered at a steep, close-out discount. It is convertible from a pannier to a backpack. It has some plastic clips that lock it to the rack on the bike quickly and easily. The bag is made of some rubberized (?) nylon with a top that rolls up and keeps whatever you carry dry, even in pouring rain. I carry my ancient, heavy, thick, Thinkpad laptop to work in it every day, and it can hold quite a lot of groceries.

I also have a small bag from REI that I've had for many years that fits under the seat for emergency tools. I don't have it on the bike all the time- just when I'm going on longer rides. Someday I'll probably regret not using it all the time.


I have a Pearl Izumi bike jacket that I have been using for many years. It's waterproof and breathable, has long sleeves that cover my arms even when stretched out on the bike, and and extended "tail" that covers my lower back in riding position. It's a great jacket, except for one thing- it has no pockets! That is a never ending source of frustration for me. I have looked at many other biking jackets and find that about half of what's out there has no pockets or just one pocket at the lower back. What are they thinking? Real people have to carry stuff when they are riding. There isn't always someone in a sag wagon driving along behind the riders to carry their crap.

I swapped the PCO seat for the Serfas Rx seat from the old Cannondale I was riding because the PCO seat just wasn't very comfortable for my pelvic geometry. The Serfas seat is split down the center and the two halves can rotate to conform to the shape of your (my) ass bones. The padding on the seat is very dense, not squishy, and is comfortable even on long rides.

I also bought a pair of Ergon GP1 grips to replace the ones that came on the PCO. I was finding that my hands were getting numb after a few miles of riding with the original grips.

I added a cheapo water bottle cage - nothing special, but it does the job.


Fortunately there isn't much to do to the bike, and I was already well equipped with metric tools that I have collected over many years of working on bikes, cars, 3D printers, and electronics. I do carry a small multi tool when I ride for just-in-case. I also carry a CO2 inflator, patch kit and tire levers. I haven't had a flat since I got the PCO, and haven't had to touch anything else, either, except for dialing in the seat height and mounting the mirror and Ergon grips. The bike has 15mm nuts on the axles and no quick release, so I should start carrying a 15mm wrench, too. Priority Bicycles supplied a decent 15mm wrench with the bike.

Sette multitool with uSD card for scale. I got this tool from Pricepoint many years ago. No, the uSD card didn't come with the tool.

A few years ago I bought a 3D printer that came with a set of hex screwdrivers. I had never heard of the brand- Bondhus- but I was impressed with them. I looked them up and it turns out you can buy them on I have since bought another set of the hex drivers and torx drivers because they are good and inexpensive- much better quality than anything from I ever got at Harbor Freight Tools. I have yet to break or damage any of them and they are much more comfortable to use than the L shaped drivers, though they don't fit everywhere an L shaped tool will fit.

I have to say the best, recent tool acquisition was the Ryobi One+ high pressure inflator that has replaced my crappy old floor pump. OMG it is fantastic! No more struggling with a floor pump to try to maintain tire pressure. A quick 10 second squeeze of the trigger tops off each tire and I'm ready to roll without working up a sweat before I even start to ride. If you have any of the Ryobi One+ tools/batteries, and you have a bicycle in your household, this one should be your next new tool. I paid $25 for it and feel like it was the best $25 I have spent in a long time.

When I repaired the flat tire on the rear wheel, the Ryobi inflator made quick, easy work of refilling the tire. I can't say enough good stuff about this tool!

Monday, May 17, 2021

No more floor pump for me!

 About a year ago I decided it was long past time to replace my ancient DeWalt 12V drill/driver as the battery was failing. I did some research and decided to buy an 18V, brushless Ryobi P252 that came with two, 2Ah Li ion batteries and a charger for about the same price as a replacement NiMH battery for the DeWalt unit.

The Ryobi driver is great. It's small, light, and very powerful thanks to Li ion batteries and the brushless motor. It has a white LED that lights up the work and a magnetic tray for holding bits or screws.

Here's a review of the driver:

A few months ago I was anticipating an upholstery project and I wanted to get a stapler so I did more looking. I ended up buying a Ryobi electric stapler that uses the same 18V batteries that the drill uses. The stapler slams staples deep into hardwood like it's butter!

The stapler is every bit as good as the drill/driver.

Here's a review of the stapler:

I got a new bike in March and have been using an old floor pump I've had for about 15 years to keep the tires topped up. The floor pump is a stupid design that has a screw holding the metal tube into the plastic base of the pump. The screw goes into the high pressure area and had a rubber seal that was leaking. I replaced the seal with a couple thick o-rings and some plumber's grease but no good- it still leaked. I had to pump that dumb thing a lot to get a little air into the tire as the pressure was going up, and I could hear it leaking at the screw with each stroke, as if it were laughing at my effort.

I decided to look for a replacement for the floor pump. After a bit more research I found that Ryobi makes a high pressure inflator that uses the same 18V batteries as the drill and stapler. Perfect! I picked one up at Home Depot for $25- less than the cost of a decent floor pump, and cheaper than ordering it via amazon. 

The inflator can pump up to 150 psi and has a duty cycle limit of 5 minutes on/5 minutes off to prevent overheating.

I noticed a couple things about it as soon as I opened the box and connected a battery:

1) there's no lock-out on the trigger, so a very light touch will start the thing up. Don't transport it loosely in your car with a battery attached!

2) the locking chuck on the end of the hose is kind of cheesy looking. 

Other than that, it seems to be well made. It's not exactly quiet, but it really isn't too noisy either. Best of all, it takes my bike's 700x32C tires from 60 psi to 80 psi in about 10 seconds. It has a big, easy to read, backlit digital pressure gauge that lights up whenever I squeeze the trigger. 

Here's a review of the inflator that will give you some idea of operation:

I think floor pumps are officially obsolete! I don't think I'd try to inflate a car's tires with it, but it's perfect for bikes.

Before you ask, no, I am not receiving any sort of compensation for this post- I just like these tools and thought I'd share. Also, I'm just someone who does a lot of hobby stuff and find these tools more than adequate for my needs.

Tuesday, May 4, 2021

Another Printed Lamp

To a hammer, everything looks like a nail. To someone with a 3D printer, everything looks like an opportunity to print. I needed a new lamp, so, of course, I printed it.

I started with a single walled PETG vase that's about 250mm in diameter and 600 mm tall. I used a edge-glow glass PETG filament from Keene Village Plastics that has a little blue dye added to make it look like old Coke bottle glass. I printed with a 1 mm nozzle, 1.2 mm line width, and 0.6 mm layers. The vase took about 8 hours to print at 30 mm/sec.

The vase on the printer- almost uses the entire print capacity of the machine.

The bulb is a 300 mm long x 30 mm diameter, dimmable, "Edison" type antique-looking thing I picked up via It has two linear LED "filaments" that use 12W and produce 4000K light.

The bulb screws into a socket that is positioned by another printed part to put the "filament" at the vertical and axial center of the vase. 

I added a printed "shade" that fits on the bulb itself. It, too, is PETG, in this case purple. Its purpose is to protect your eyes from the bright bulb filaments while adding some color for visual interest. The shade is a cylinder with a 90 degree section cut out and facing the wall. The lamp lights up the wall behind it and the shade appears red (yes, purple filament) from every other direction. I operated the bulb at full brightness for several hours and the plastic shade is not affected by the heat from the bulb.

No, that's not a white balance problem- the brick is cream colored (old buildings in Milwaukee were made using cream colored bricks) and the shade does look red, not purple, probably an interaction between the 4000K light from the bulb and the purple shade.

Light bulb with purple shade fitted. The bulb only warms slightly in operation so it poses no danger of melting the PETG. The shade is sized to fit on the 30 mm diameter bulb and to just cover the length of the LED "filaments".

This is what it looks like in daylight with the lamp off. Note- the shade is purple. The bulb and shade are positioned at the exact axial center of the outer vase.

Another view of the lamp in daylight. The outer vase is very glossy

The vase design was made by combining two twisted designs- one right handed twist, the other left handed twist. That resulted in an easy to print, pleasing shape that produces some interesting reflections of whatever light is in the room.

Sunday, April 25, 2021

Just a dumb little thing

I lock my bike with a Kryptonite Evolution mini 7 lock and cable. The lock comes with a bracket to carry it on the bike frame. It also comes with a couple little rubber "bumpers" that are supposed to keep the lock from rattling when it's in the bracket while you ride. Naturally, I quickly lost one of the not-so-tight-fitting bumpers and the lock was rattling up a storm every time I rode. That was really annoying because the bike is almost completely silent otherwise. I did what anyone with a 3D printer would do and I "designed" a printable bumper to replace both of the ones supplied by Kryptonite.

I made my bumpers fit tighter and a little longer than the original because the original still allowed some rattling. The tighter fit will keep me from losing it, and the additional height really prevents rattling.

Here's my "design":

I took advantage of the fact that holes print small and made the inside diameter 13 mm, exactly the same as the lock, which means it will fit tightly when it goes on the lock. The outside diameter is 19 mm, and the length (height?) is 8 mm (the original was 7mm high).

I printed a couple of bumpers using TPU filament in about 5 minutes. They fit perfectly and prevent all rattling!

Anti rattle bumpers- mine and the original.

New anti rattle bumpers in place.

Sunday, April 18, 2021

New Lights for the Kitchen

 My groovy, shag-a-delic pad in town had some small pendant lamps hanging from the ceiling to light up the kitchen island. They were not particularly interesting, and they didn't really seem to work with the industrial nature of the building, mostly because they were so small. I originally planned to replace the small painted glass shades with larger printed shades, but then I found a couple big aluminum reflectors for some industrial ceiling lamps at the makerspace in very good condition. 

All I had to do was clean the dust off them in the shower and design and print some simple brackets to allow them to mount on the hanging sockets that were already in place.  I made a few quick measurements and got to work in Fusion360. This is what I came up with:

I printed a pair of them in PETG and hung up the reflectors.

Here's one of the reflectors with the bracket mounted. The reflector is 435 mm in diameter at the bottom edge, and about 300 mm high. The reflectors have little horizontal grooves, almost as if they were 3D printed.

The bracket is extra beefy and absolutely will not have a problem holding up the reflector.

The bracket attaches with 4 plastic anchor screws using the mounting points that were already provided in the reflectors.

Here it is with a warm, antique looking LED bulb that's about 200 mm long. 

Here is a conventional type LED bulb. The reflector directs most of the light downward.

This bulb is a 300mm long 5000K type that is quite bright. The reflector tends to throw a lot of the light off to the sides as well as downward. It's a little harsh because the light shines directly into your eyes no matter where you sit or stand.

The is the island lit by the two new fixtures and a couple 800 lumen, conventional LED bulbs.

Here it is with the original lamp in the center also lit.

I think the original lamps were just too small. They didn't look right with the big ventilation pipe and the large rafters.

Two of the new reflectors throw plenty of light, so it's no problem if I can't find a third reflector. I haven't decided if I am going to remove the middle pendant completely or leave it in place.

Monday, March 29, 2021

Oops! A Sand Table Disaster

Progress on the smaller sand table, Arrakis, was recently brought to a standstill. There was an incident...

The mechanism was working fine so I was working on the sand box. I got it mostly assembled and discovered that I had underestimated the protrusion of the rivets holding the box corners together and as a result, I had to take the mechanism apart and reduce it's size slightly to get the sandbox to fit properly. The disassembly, modification, and reassembly went fine, and then I powered up the machine for testing. 

The machine homed as it should, so I selected a pattern file forgetting that the dimensions of the table are now smaller than the pattern. The magnet took off and when it hit the end of motion because the table was now slightly smaller, I heard a pop, saw a spark and the whole thing shut down.

I found the Duet board had let the smoke out of a voltage regulator chip. I ordered a replacement regulator chip and installed it, but the board was still dead. Apparently more than just the regulator chip blew. I decided not to expend any more effort trying to revive the board- it was toast. I ordered a replacement.

I also checked the 200W power supply. The output on indicator LED was pulsating instead of being on continuously. Voltage out read around 12V that bounced up and down a volt or so. It was supposed to be a 24V supply.  Hmmm. I ordered a replacement.

I tested both motors and they appear to be OK, as does the smaller 150W power supply that was powering the other motor.

What happened?

DC42 at Duet3D forum has what is probably the best explanation for what happened:

"My guess is that when the servo motor hit the hard stop, it first increased the current to maximum to try to overcome the resistance. When that failed, it turned the current off, at which time all the energy stored in the motor inductance was dumped into the power supply rails, causing a voltage spike that blew both the PSU and the Duet. The stepper driver chips and the fan mosfets on the Duet are rated at 30V, although if the drivers are not energised then in theory they can take 60V. The capacitors on the VIN line are rated at either 35V or 50V. Your PSU most likely had output capacitors rated at 35V."

Now what?

I ordered replacements for the Duet controller and the power supply. Since back EMF from the motors can cause a problem if you exceed their rpm specs or suddenly block the motion (apparently), I decided to add a third, small power supply exclusively for the Duet board. That way, any mishap in the motion system won't end up killing the controller board again. I'll add some high voltage capacitance to the motor power rails, too.

I will still power the LEDs from the new 200W motor power supply as they use buck converters that are able to withstand much higher voltage input so the LEDs and buck converters aren't likely to be damaged in another "incident".

Engineering Solution

yngndrw at the Duet3D forum posted this link for a circuit designed to protect the motor driver and power supply in the event of an unexpected sudden stop. I will be adding a couple of these to protect the power supplies and motor drivers.

Essentially, this circuit shunts current from the motor to ground whenever the back EMF from the motor exceeds the power supply voltage. That will protect anything sharing the power bus with the motor.

Update 4/12/21

The mechanism is back up and running with the new controller board on its own power supply. I haven't put the protection circuits together yet, but that's coming up as I gather the parts. More to come...

Saturday, March 27, 2021

New Bike: Priority Continuum Onyx

Update 7/19/21:

I've been riding the bike daily on my commute to work and occasional trips to the makerspace for almost 4 months. The only issue I have is that the front brake squeals loudly now (a problem easily remedied with some disc brake cleaner- see: ). I replaced the seat and hand grips with slightly more comfortable ones, otherwise the bike is as it arrived from Priority. It has been 100% reliable and has required no maintenance, other than addressing the brake squeal. The hub shifts perfectly and the drive belt is smooth and quiet.

Now back to the original post:

I recently moved from a rural/suburban house that was 40 km from the clinic where I work to a loft in a 100+ year old factory building that's just a two km (6 minutes by bike!) from work, so I started commuting by bicycle, even going home for lunch most days. This location is no more than 15 minutes by bike from almost anything and everything you'd ever want to see or do in Milwaukee.

I've been riding a 30 year old Cannondale hybrid bike that someone gave me about 8 years ago for helping them with a project at the Makerspace. The bike is modified from the original 3x8 gear setup- someone installed a Sachs 3 speed hub with a 7 gear cluster on the rear end of the bike and removed one chainring and the front derailleur and shifter. Unfortunately, they also "modified" -i.e. wrecked-  the rear dropouts and the rear wheel axle no longer has a well defined position- it now relies on super tight wheel bolts to hold it in place. That allows the wheel to shift a bit in the dropouts under hard pedaling in low gear which pushes the wheel against one of the brake pads. It doesn't go back until I take a wrench to the wheel bolts and straighten it again, then wait for the next time it shifts. I can usually ride for a few weeks before the wheel shifts in the dropouts, but ugh! 

The rear derailleur looks like it has been bashed a few times and can't be straightened out or adjusted to work reliably any more. The bike just wasn't worth the expense to fix all the problems.

I still have the CF recumbent bike I built 15 years ago, but it isn't real practical for urban commuting, especially considering the hill I live on, so it was time to find a more practical commuter. I wear regular clothes when I ride so I wanted to find a belt driven bike that wouldn't get oil all over my pants and would require minimal maintenance. Derailleurs don't work with belt drive, so if you want belt drive and multiple gears, you have to have an internally geared hub (IGH). That limited the choices to just a few bikes, including the Marin Presidio 3, the Priority Continuum Onyx, and few others that I ultimately ruled out as too cheesy, too expensive, or just not what I wanted.

There are different belt drive system makers out there, but the best known quality brand is Gates (the same Gates that makes the belts in my 3D printer). Gates belt drive system is called "Carbon Drive" because the belts are reinforced with carbon fibers. Here's a long, but partial list of bikes that use Gates carbon drive. There are some cheaper, Chinese-made/branded bikes that use belt drive, too, but not the Gates drive that is the standard to which others are compared. A company called Veer makes a belt drive system that can be adapted to work on almost any bike.

The Marin Presidio 3 uses a Shimano Nexus 8D 8-speed IGH that has a pretty good reputation for reliability, requires minimal adjustment or maintenance, and a 306% gear range. It also uses a Gates belt drive. I'd have to add fenders for riding in less than optimal weather, but I could probably steal the Planet Bike fenders off the old Cannondale I've been riding.

The Marin Presidio 3- comes with Shimano Nexus 8D rear hub, Gates CDN belt drive, and Shimano hydraulic disc brakes.

I was ready to order the Presidio 3, but a few calls to bike shops in Milwaukee/Chicago area that are supposed to be Marin dealers left me wondering why no one wanted to take my money. I gave up and went back to my search.

That's when I found the Priority Continuum Onyx (I will refer to it as PCO hereafter). It had everything I wanted - belt drive, IGH, and fenders, and a few things I hadn't really thought about like head and tail lights powered by a dynamo in the front wheel hub, and hydraulic disc brakes! Add a rack (that I ordered with the bike) to the rear end and it looks like the perfect commuter bike.

The Priority Continuum Onyx, supplied with Enviolo CVT rear hub and Gates CDN belt drive system, Promax hydraulic disc brakes, dynamo powered lights, fenders, and kick stand. This photo is from the Priority web site. The kickstand on my bike mounts on the rear wheel stay, not at the bottom bracket as shown here.

The PCO has an Enviolo continuously variable transmission (used to be called NuVinci) that is used in some e-bikes. It provides a 380% gear range- slightly wider range than the Shimano Nexus 8D on the Marin bike. The Enviolo hub doesn't shift in discrete gear ratio steps- it's continuously variable between the minimum and maximum gear ratios. It can be shifted while pedaling under load, while standing still (but as I found out, only through about 1/3 of the total gear range), or while rolling without pedaling. This video explains how it works:


The Enviolo hub is sealed and permanently lubricated, so it is a zero maintenance drive. If you were paying attention to the video, you may have noticed that the guts of the hub are mostly steel- it weighs 2.45 kg (5.4 lbs). That makes it pretty heavy - the whole Continuum Onyx bike weighs in at 31 lbs (including the fenders and pedals), so it's not super light, but not too bad. If you pick it up it definitely feels heavier at the rear end thanks to the Enviolo hub.

Note that the Enviolo hub doesn't have any gears- it uses tilting steel balls and steel input and output rings to achieve the variable drive. In theory the "lubricant" keeps the balls and rings from contacting each other (this is traction drive, not friction drive- there's a difference), so they should / better last a long time. The rear hub comes with a 2 year warranty, so I'm not too concerned about it wearing out.

For those interested in the chain and derailleur vs chain and IGH vs Enviolo/Nuvinci efficiency, there's an interesting article here. The NuVinci//Enviolo hub is the least efficient type tested by about 6% depending on the selected gear ratio, but in the real world it isn't likely to matter. Reliability and reduced maintenance are worth a little extra pedaling effort to me. If I didn't want to expend any effort, I would have ordered an e-bike.

Belt Drive vs Chain Drive

Here's a great video that compares belt and chain drive by someone who knows what he's talking about (remember when that used to matter?):  

Gates has a couple videos on their website comparing chain and belt drive systems. When both are new, the chain is about 0.5% more efficient than a belt drive, but as the chain and belt wear, the belt drive remains almost a efficient as new, and the chain gets much worse.

Order and Wait

I ordered the PCO and Axiom rear cargo rack in January but thanks to excessive demand and delayed shipping due to COVID I had to wait for shipment until the end of February. I was OK with that- it was cold and snowy outside and I wasn't going to be riding in that kind of weather anyway. A couple weeks after I ordered, I received an email explaining that the bike was going to be delayed and would ship by March 15th. I was a little disappointed, but there really was no hurry. 

Shortly after I ordered, the price for new orders went up $100 and shipping was now moved out to the end of May. I'm glad I ordered when I did!

On March 11th I received another email announcing that the bike was shipping and would be delivered by March 16th! Woohoo!  When the bike arrived I set about unpacking it and assembling it. The unpacking takes some effort- they packed it up very well so there would be no damage in shipping. It came out of all the packaging in perfect condition. 


The bike came 90% assembled- all I had to do was mount the handlebars, the front brake disc, the front wheel, the seat, the pedals, and the front fender. Assembly was easy- just follow the video on the Priority bikes web site. They supply better than adequate tools to do the job, but of course, I had my own that I preferred so I used them. One thing I haven't seen before is that many of the bolts have torque specs marked right on the bike's frame. Nice! Now I should probably get a better torque wrench...

The tool kit that came with my bike. Left to right: touch-up paint, 8 mm wrench, wire nut(?), 4mm star driver (for the brakes?), 3mm hex key, 4mm hex key, 5 mm hex key, 6 mm hex key, 15 mm wrench and 10 mm wrench.


I put some anti-seize compound on the pedal's threads before mounting so I'll be able to get them off again if they ever need replacement, and used Lock-tite on the screws that mount the rack to ensure they'd stay put.

I had some minor adjustment issues with the front disc brake pads rubbing slightly, but I was able to sort it out with some on-line videos from Priority bikes and Park Tools. The brake owner's manual that I downloaded from the manufacturer's web site said they should be worn-in a little to maximize stopping power and to match the pads to the discs. I followed their procedure to align the calipers to the disc and wear-in the pads and the slight rubbing went away.

The bike has a threadless headset which means that the cap on the steerer tube is used to set the preload on the headset bearings. You loosen the screws on the handlebar stem so it rotates freely on the steerer tube, then tighten the cap screw which pushes the stem down as it pulls the steerer up, loading the headset bearings, and finally tighten the screws on the stem. If the preload is too light, when you lock the front brake and push the bike back and forth in the front-rear directions, you'll feel play in the headset bearings. If it's too tight steering will be stiff. When it's just right, steering will be free and there won't be any play in the headset bearings.

I spent about an hour assembling and testing everything.


I've seen all the on-line reviews of the PCO and found them lacking certain information I would like to have known before I bought the bike.  I couldn't find any mention of the model of hydraulic brakes - only that they are made by Tektro (the brakes that were on my bike are actually made by Promax). I haven't had a bike with hydraulic disc brakes before, so I'm curious about maintenance and adjustments. I was also curious about the wiring to the lights and how well it's sealed against the weather. I could find no mention of the tooth count on the crank ring or the rear hub belt ring, and not many close up photos that allow them to be counted, which meant I couldn't calculate the exact gear-inch range (does anyone still use that?) that came on the bike. I also wanted to know how the gear ratio range compares to that in my old bike. 

Consider this "review" the one that provides that missing information. If there's any detail you want to know about that you don't see here, ask in the comments below and I'll update this post with photos and measurements as requested. The photos are all from the bike as I received it, but of course, supplied components may change depending on when you order and availability of parts.

Lights and Reflectors

In urban locations, where streets are usually well lit at night, you mainly need lights to alert drivers to your presence. I live and ride in such a location. The headlight that comes on the PCO does a pretty good job of lighting up the road so you can steer around the potholes, etc., and one of the three LEDs stays on for a few minutes when you come to a stop. The red taillight flashes as long as the bike is rolling, even if you're just walking the bike.

The headlight in older PCOs was mounted on the fender bolt on the fork. In the latest bikes, for some reason, they moved it up to the handlebars where it tends to light up the brake cables and casts their shadows on the road. It used to mount with the wires on the bottom side of the light, now the wires and rubber seals are on the top side. That doesn't seem like a good idea to me because it invites water to sit on the wire/seal. 

The headlight has 3 LEDs. When you are riding very slowly, like when you're climbing a steep hill, the lights flicker a lot. At more normal speeds they are on steadily. When you come to a stop, two of the LEDs shut off and one remains lit for a few minutes, powered by an internal supercapacitor.

The headlight wires run through a cable jacket to the top side of the light. You can see the power switch for the light and the cover for the USB port that can be used to charge accessories when the light is switched off.

When I was riding the old Cannondale, I covered a large portion of the frame and wheel rims with reflective tape. That made me more visible at night and covered the Cannondale logos to make the bike less attractive to thieves. I used a set of Cygolite HotRod lights to increase the chances I would be seen while I was on the streets at night. 

The frame of the PCO is painted matte black with reflective logos. It looks great, but it's not ideal for visibility, so I may add some reflective tape. Moving reflectors are more noticeable than fixed reflectors, so I added reflective tape to the wheel rims like the old Cannondale. The reflective tape I used is the same red and white stuff they put on truck trailers (look for "conspicuity tape DOT-C2"), so it lasts for years and is extremely efficient at reflecting light from every angle. It sticks fine to flat or concave surfaces, but don't try to bend it over a convex surface- the edges will peel up.

The tail light.  It flashes whenever the bike is rolling, even at walking speed. It is 59 cm (23") above the ground. The cable is routed on the underside of the fender. pardon the dirt, but this is a bike that gets ridden in weather.

The reflective Priority logo on the top tube of the frame is discrete in daylight but really stands out at night.

The wheels have 36 spokes so there are 36 spaces between them to add the tape. I cut a bunch of red and white reflective strips to fit (40 mm x 8mm), wiped the rims with isopropyl alcohol, then mounted the reflective stickers. I made one half of each wheel red and the other half white, figuring that as it rotates the color change will make it more noticeable. 

Red and white reflective tape added between the spokes on both wheels, and a big piece of red tape on the back of the rack. Yes, that's just reflected light!

Yes, reflectors work without any power source but the light that hits them!

Amazon sells these spoke mounted reflectors that look interesting, as well as a lot of different pre-cut reflective tape assortments in several different colors.

The bike comes with the legally required front and rear reflectors and one reflector for each wheel. I left off the red rear reflector in favor of a much larger piece of red reflective tape stuck to the back of the rack.


My bike came with Promax Solve hydraulic disc brakes. I haven't ridden a bike with hydraulic disc brakes before and was pleasantly surprised by the solid feel and stopping power. There's no flex or squishiness when you squeeze the brake levers - the bike just slows or stops. Braking is very smooth and predictable. It turns out there isn't much to adjust until the thing fails by leaking fluid, or you break a lever or bend a brake disc when the bike falls over or crashes.

Left side brake lever and grip. This lever controls the front brake. The grips are some high density foam that feels pretty good on bare hands. They're soft enough to provide some cushion but not squishy.

Right side brake lever, grip, and shifter. This lever controls the rear brake.

The rear Promax Solve brake caliper. The only adjustment is aligning the caliper with the brake disc which is done by loosening the mounting bolts, squeezing and holding the brake lever, then tightening the mounting bolts.

The front brake caliper mounts on the fork while the rear brake caliper mounts on the sliding dropout so that it remains aligned with the disc on the wheel even when the wheel is shifted backward to tension the drive belt.


My bike came with Wellgo K79 B087 aluminum platform pedals that have studs cast right into the body. They have nicely sealed bearings that should be impervious to weather. I put a little anti-seize compound on them before I screwed them into the cranks so that I'll be able to get them off again if I ever need to.

One of the pedals. Plenty of cast-in studs to keep your feet from slipping. That flat area in the center is where the Welgo logo would go.

The markings indicate Wellgo K79 B087 pedals. They made of cast (?) aluminum, have sealed bearings, and yellow reflectors.

Belt Drive

The bike came with the Gates CDN belt drive system including a 50 tooth, 5-bolt, composite drive cog and a 24 tooth CDX steel rear cog,  model S-150 175 mm cranks, and a 118 tooth CDN center groove belt. There's a manual on the belt drive with the bike that says the CDN belt is good between -20 to +60C (-4F and 140F).  If you need wider temperature range, the CDX belt is rated for -53 to +85C (-65F to 185F). The rear wheel mounts have vertical dropouts that can slide in horizontal slots with adjusting screws that are used to tension the belt and align the wheel with the bike's frame. There's a complete technical manual that covers all the Gates Carbon Drive products here.

Gates has a phone app that can be used to check and adjust the belt tension. I tried it in my phone and found the belt's resonant frequency to be 58 Hz, a little higher than the recommended value indicating tension was a little too high, so I loosened up the belt a little until the app indicated a 45 Hz resonance.

The Gates web site has an excellent calculator that lets you figure out what the available gear ratios mean in terms of speed when riding. Here's an example I ran based on the hardware supplied on my bike:

I assume that the calculation takes the minimum and maximum gear ratios of the Enviolo hub into account when calculating speed vs cadence. Cadence between 30 and 80 seems like a reasonable range for my riding. I'm not a strong rider and probably can't maintain a cadence of 80 in a high gear unless I've got the wind at my back and/or going down hill. 30-60 is probably closer to my normal range.

Labeling on the drive belt. Yup, CDN, 118 teeth.

Gates 175 mm model S150 crankset with 50 tooth drive cog. This crank fits on a sealed bearing, square-axle bottom bracket, probably also made by Gates.


My bike came with WTB Slick 700 x 32C tires with very reflective side walls. They seem to reflect light very efficiently. I wonder if the reflective properties wear off from flexing and shedding glass beads. I wasn't able to find any info about that, just lots of ads for tires with reflective sidewalls.

If you want to swap in fatter tires, the frame and fork look like there's plenty of width, but the new tire has to fit under the fender. The fenders are 46 mm wide and supported by steel stays. As tire width increases, diameter also increases. While the frame and fork are wide enough for fatter tires, the vertical clearance under the fenders may limit the maximum tire width. The clearance looks sufficient for 37 mm wide tires. 

The tubes have Schrader valves.

This is the tire tread.  It rolls quietly.


The wheel rims appear to be double wall aluminum, matte black like the rest of the bike, and have eyeletted spoke holes. Spokes appear to be painted black, and I noticed that paint is chipped at some spoke crossing points. Maybe that's why the tool kit came with touchup paint. Nipples are zinc/chrome (?) plated as are the eyelets. 

The front wheel has a built-in 6V, 3W generator (which implies 500 mA current output) that powers the head and tail lights. The rear wheel has the Enviolo hub. Both are set up for disc brakes with 160 mm discs. Wheels bolt to the fork and frame with standard 15mm nuts- no quick release. If you want to be able to repair flat tires on the road, you'd better carry a 15 mm wrench. 

Spokes are arranged in a triple cross pattern on the front wheel and a double cross pattern on the rear wheel. The double cross pattern on the rear wheel is necessitated by the large flange diameter of the Enviolo hub.

This is what the wheel rims look like. The sidewall of the tire is very reflective, as are the red and white bits of reflective tape I added to the center of the rims. Each wheel comes with a white reflector mounted on the spokes.

Front hub with built in dynamo. I hope it is well sealed against weather and especially salt incursion. I would think it would be best to install it with the connector at the bottom and then put a drip loop in the wire. The connector on the end of the wires is not sealed- maybe it should be.

The Enviolo hub is completely sealed- there are no ports to change "oil". It doesn't actually use oil- it uses a nonlinear fluid that solidifies under pressure between the balls and input and output rings inside the hub. Oil would probably be the last thing you want in there! The hub is 100% maintenance free.

You can get a look at the Owner's Manual for the Enviolo hub here, and the technical manual here. When I was looking at some troubleshooting info on their website, I saw something about rattling noises coming from the hub when coasting in low gear are normal. I have not heard any such noise, but maybe it's masked by the clicking of the freewheel. 

The Shifter

The shifter and grip.

Shifting from highest to lowest gear requires twisting the shifter about 280 degrees- not something you're likely to be able to do in a single twist. The hub doesn't care about whether you're pedaling, but when you're stopped, you can only shift through about 1/3 of the entire range (don't worry, it's enough). When the bike is rolling you can shift through the entire range, pedaling or not. When you're pedaling hard and shifting to a higher gear, you can feel some resistance in the shifter, but it shifts quickly and the resistance in the shifter disappears at the same time.

The gear display on the shifter is cute, but not really useful for an individual who owns the bike. Yes, it will show you the gear the bike is in when you start to use it, but it shifts so easily, you don't need to know where the gear is ahead of time- you'll know as soon as you push on the pedals. Or just get in the habit of twisting the gear shift to a lower gear every time you get on or off the bike. After the first 30 seconds of looking at the display while you shift, you won't need to look at it again. I suspect the indicator is there for fleet and rental bikes that will be ridden by people who are not accustomed to riding bicycles.

Seat and Post

The seat is a narrow but reasonably comfortable part with a central groove to relieve pressure on my soft parts. It might not be an ideal seat for women due to the narrow spacing of the pads. There doesn't appear to be any indication of the manufacturer or model of the seat marked on it, but the Priority Bikes web site says it is a "Velo Dual Density"

The seat post, for some reason, is made of carbon fiber tubing, but it isn't obvious to look at it, so it shouldn't attract thieves. It has a two-screw micro adjusting seat clamp that is very secure. The seat post is held in place with a screw-down clamp on the top of the frame's seat tube. If someone wants to steal the seat they'll need to bring a tool. I wouldn't put it past some thieves to do something like that, and you can buy special screws that have unique heads that require a key to unscrew them, but there are two more ordinary bolts holding the seat. So even if you secure the seat post with a special screw, they're going to take the seat. How many special keys do you want to carry around (and never lose)? If you're really worried about it, get a quick release clamp and take the seat and post with you when you lock the bike (but then they'll steal the clamp!).

The seat post and clamp.  You wouldn't know the post is CF to look at it.

It's nice looking and relatively comfortable at least for the rides I've done so far, up to about 20km.

Another one of those nice torque specs marked right where you need it.

I noticed that with the angle I have set the seat, there is a depression in its center that pools rain water. It might be nicer if the seat had a hole in the center to let it drain.


The fenders are plastic, 46 mm wide, and painted matte black to match the rest of the bike and the hardware (stainless steel?) looks like that supplied with Planet Bike fenders of the type I installed on the old Cannondale. The rear fender has a red LED taillight and wire to the dynamo attached along its inside surface, out of sight, but right where crud from the road will be thrown against it. We'll see if the cable lasts...

Looks like a Planet Bike fender to me! It's got a nice Priority logo mud flap and ever a nice trim piece at the front edge of the fender.


I ordered the Axiom rack when I ordered the bike. It was shipped separately and arrived a day after the bike. I chose that rack because it is solidly built and the mounting system pushes the whole thing back a few cm to reduce the chance of your heels hitting panniers as you pedal.

The rack is made from 10.4 mm aluminum tubing, painted black like the bike. It's very sturdy, fits the bike perfectly, and holds panniers far enough back that you'll never hit the bags with your heels when you pedal. Some of the rivets visible on the fender are used to hold the wire for the tail light.

I also ordered a bag that was offered at a steep close-out discount from Timbuktu to go on the rack. It's a weatherproof convertible pannier/backpack that's big enough to carry my laptop computer and some other junk, but unfortunately, the attachment system doesn't fit the Axiom rack very well. It's less than optimal, but workable, so I'll keep using it. It beats the hell out of carrying the anything in a bag on my back!


The Kickstand

The kickstand deserves special mention. It is the beefiest kickstand I have ever seen on a bicycle! I think it would be right at home on a Harley-Davidson! It mounts on the left wheel stay with two screws, not immediately behind the bottom bracket as the Priority bike photos show. 

This is MUCH better!  If the kickstand were mounted in the usual place and in the usual way with a single bolt, would require kicking it up in order to roll the bike backwards otherwise the left crank arm would hit it. The single bolt would have a tendency to loosen and then the kickstand would keep pivoting on the bolt until you retightened it. When it's bolted to the wheel stay, it can't hit the crank arm, so you can roll the bike backwards without first kicking up the stand, and it can't pivot around the two mounting screws. 

I have managed to hit the kickstand with my heel while pedaling a couple times.

It has a big tough plastic/rubber foot that won't damage your floors if you park your bike inside your home.

That's what I call a kickstand!

The Frame

The frame is aluminum and  seems to be well made, with no attempt to smooth the welds at the joints. The old Cannondale frame had the welds ground smooth and it looked almost like it was molded as a single piece instead of welded. That's one reason why Cannondale bikes are as expensive as they tend to be. 

The rear brake tube (not cable- the brakes are hydraulic) is routed inside the top tube and the shifter cables and taillight wires are routed inside the down tube. The frame has some nice, welded-on brake cable guides on the left rear seat stay and the front fork.

Rear brake tube routing in the top tube of the frame

Rear brake tube mounting in the top tube of the frame.

There are screws to mount water bottle cages on the seat and down tubes, and attachment screws for racks on the rear dropouts and the front fork.

The paint is a beautiful matte black that appears to be skillfully applied and finished. There are reflective Priority logos on the top tube, belt and wheel stays, and the steerer tube. There are also two pieces of black reflective tape (yes, really) on the seat stays.

In order to mount the belt there has to be a cut in the frame because the belt is a continuous loop and has no pins you can pull out like a chain. The right side wheel mount/dropout is split and held together with two screws. If you ever need to replace the belt, you open the frame at that point, remove the old belt, put in the new one and screw it back together. 

Left side rear wheel mount. The brake caliper mounts on the dropout with the wheel axle, not the bike frame. When you adjust the belt tension by sliding the dropout back, the brake and wheel stay aligned to each other because they are mounted in the same piece of metal.

Right side rear wheel mount, annotated.  The actual dropout is a separate piece with a vertical slot that the axle fits into and is mounted behind the horizontal slot in the frame. It can slide in the slot, pushed back by the belt tension adjuster screw, and is then held in place with the two dropout fixing screws. You can see the split line in the frame that allows the belt to be replaced and the two bolts that hold it together.

Also because it is a belt drive, some provision has to be made to allow it to be tensioned. The rear wheel mounts use dropouts with vertical slots that the axle fits into. Those dropouts can slide in horizontal slots in the frame to allow the belt to be tensioned, and then they screw down tightly using the dropout fixing screws. The rear brake caliper mounts on the sliding dropout with the wheel so it stays aligned with the disc without being affected by belt tension adjustment.

It appears that all the hardware is stainless steel, and hopefully won't rust much if at all.

The serial number is stamped or milled into the frame, and appears on a  barcode sticker under the bottom bracket.

The Ride

I've been riding the bike for a couple weeks and find that the PCO is more comfortable than the Cannondale it replaced, and I love the shifter and brakes. The Enviolo hub is great- I'm no longer stuck in a slightly too high or too low gear, and I find myself changing the gear ratio much more often to exactly where I feel most comfortable pedaling. The low gear is plenty low to get me up the hills and the high gear gets me going as fast as I ever want to go. 

The only noise that the bike makes when pedaling is the tires on the road (as long and the lock isn't rattling). The belt drive and Enviolo hub are silent even when shifting. The freewheel clicks when you coast, of course. I've noticed that on particularly rough roads the kickstand rattles a bit.


The roads are in really bad shape here, so I may put the slightly fatter tires (Panaracer UrbanMax 700 x 35C) from the Cannondale bike on this one, and at least one bar-end mirror would be handy to see traffic approaching from behind. I had a split seat made by Serfas on the Cannondale that I liked, so I may swap seats.

There's no guard on the drive cog and I managed to catch my pants in it once.  As soon as I realized it I pedaled backwards and it let go- no harm done and no oil on my pants. I'll probably design and print a guard ring for the drive cog like I did for the Cannondale. 


No bike is completely maintenance free, but the PCO comes close. There's nothing to do with the sealed rear hub or the belt drive, which is most of the maintenance on most bikes, but the hydraulic disc brakes, lights, shifters, cables may require a little attention once in a while. The wheels and tires will be the main maintenance items- wheels may have to be trued occasionally after hitting potholes, and tires will have to be pumped up a bit every week or so, and flats repaired. Tires and brake shoes will wear out eventually. Overall, it's about as close to zero maintenance as you can get with a bicycle. Eventually the cogs and belt will wear out and require replacement, but they are supposed to last much longer than the chain drive parts they replace, so I don't anticipate having to replace any of them for many years.

Keeping It - Lock it up!

The bike doesn't come with a lock, of course, though you can buy one of a few sold by Priority. I used the same lock I've been using for a while- a Kryptonite Evolution Mini 7 with a companion cable. When I lock the bike, The U-lock goes through the frame and rear wheel and around the bike rack/post that I'm locking to, and the cable goes through the front wheel. I lock up on a rack in front of the clinic where I work and there's a lot of foot and car traffic, including frequent police drive-bys, so it's unlikely anyone will attempt to steal the bike while I'm at work. I can see the bike from the window of my operatory.

The Kryptonite lock comes with a bracket to mount on the bike's frame, but you still have to figure out how to carry the cable. I mounted the lock bracket on the down tube. When I was riding the Cannondale, I carried the cable on the seat post. It was convenient and easy because the seat post had quick release and when I went into work I took the seat and post with me to keep them from getting stolen. There's no quick release on the Priority seat post, so now I carry the cable in a pocket of the pannier bag. I noticed that the lock tends to rattle while I ride so I'm going to work out a way to prevent rattling when I carry the lock and cable on the bike without the bag. Maybe some Velcro tape?

This is how you lock a bike if you want to keep it. The U-lock goes through the frame and rear wheel and on the rack, and the cable gets looped through the front wheel. It would take considerable time and effort for a thief to make off with the bike, so they'll probably look for an easier target. If they have a cutoff wheel on a grinder they can cut the rack, throw the bike into a truck and work on the lock in a more private location at their leisure. If someone really wants it, they're going to get it.