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



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. 


Assembly

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.


Specs

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.


Brakes 

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.

Pedals

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.


Tires

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.



Wheels

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.


Fenders

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.

Rack

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 it 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 no matter what you do with the belt tension.

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 you hear coming from the bike when you pedal 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. 


Changes

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. 


Maintenance

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.



Friday, December 4, 2020

X Axis Wobble in UMMD

I was recently working on a smaller version of the sand table, called Arrakis, and noticed that when the magnet carriage was moving in X only, the ends of the X axis were moving back and forth about 1 mm as the magnet carriage reversed direction. I'm not sure what causes it, maybe some play in the magnet carriage on the X axis, belt stretch, flex of the X axis guide tube...


Sand table Arrakis test from Mark Rehorst on Vimeo.

Whatever the cause, it got me thinking about the possibility of the same thing happening in UMMD, also a corexy mechanism. I've never really paid attention to it, so I wrote a script to move the extruder in X only and ran it, as I had done on the sand table mechanism. I wasn't sure, but I thought I saw a tiny amount of movement. That has implications for print quality, so I wanted to test it further.

I decided to clamp a digital gauge to the Y axis guide rails, set Y to a specific value, then move the extruder carriage along the X axis and measure and movement that occurs at the ends of the X axis. I needed a custom clamp for the Accuremote digital gauge that I have used to test other aspects of mechanical performance on UMMD. I had an old DSM model of the gauge, but decided to make a new model using Fusion360 (that model is here). Once I had the gauge modeled, I dropped it into the UMMD XY stage model and designed a clamp to fit. 

Gauge and clamp models

I printed the clamp and mounted the gauge, then generated two gcode files that would move the extruder carriage in X as the gauge monitored the ends of the X axis at Y=-35 and Y=5. I started the measurements with the extruder carriage at the center of the X axis (X=0), then moved it to the right to X=145, then reversed and sent it back to the left, stopping every 5 mm and recording the gauge reading until the extruder got to X=-145. At the end the extruder returned to the center of the X axis.

The measurements were made with motion between points at 5 mm/sec, and a 3 second stop at each 5 mm test point.


Digital gauge mounted on the right side Y axis rail.


Here is the test setup with the gauge mounted on the right side Y axis guide rail. The extruder carriage is at (0,-35) where I zeroed the gauge at the start of the test runs.

 

Here is the gauge set to zero at the start of a run.

The Results

To see these graphs a little better, right click on them and select "open image in a new tab".

Graph 1: data from 3 runs with the gauge mounted on the right side Y axis guide rail at Y=-35.

Graph 2: data from 3 runs with the gauge mounted on the left side Y axis guide rail at Y=-35.
Graph 3: data from 3 runs with the gauge mounted on the right side Y axis guide rail at Y=5.

Graph 4: data from 3 runs with the gauge mounted on the left side Y axis guide rail at Y=5.


What does it all mean?

The gauge is rated for 0.03 accuracy and 0.01 mm precision. Precision applies when comparing specific data points at the different runs- i.e. comparing the value at X=50 from run 1, run 2, and run 3. So differences of +/-0.01 mm are noise and don't really mean anything. For most of the runs, most of the data at each point was within +/-0.01 mm. 

Accuracy applies to the overall position of the curves on the graph. The curve's real position may be as much as +/-0.03 mm from where they are drawn. The shapes of the curves and the differences between the maximum and minimum values should be accurate.

The waviness of each graph indicates that the ends of the X axis are moving back and forth slightly as the extruder carriage moves along the X axis, just like the sand table mechanism did, but to a much smaller degree. If you compare graph 1 and graph 2 (or graph 3 and 4) by drawing vertical lines between the two, you'll see that as one end of the X axis (one graph) moves in the negative direction, the other end (the other graph) moves in the positive direction, so the whole axis really is wobbling, with the ends of the X axis moving in opposite directions.

The X axis is maintained square to the Y axis by belt tension. The waviness of the graphs indicates that the X axis is moving slightly out of square with the Y axis as the extruder carriage moves along as if the belt tension were varying. What would cause that? Notice in each graph that the waviness moves through peaks and valleys at about 40 mm intervals. I don't think it's a coincidence that the drive pulleys move the carriage 40 mm per rotation (20 tooth pulleys and 2mm pitch belts). I suspect the main cause of the problem is crappy drive pulleys that are not accurately drilled, or it could be a bent motor shaft or two.

Notice that graph 1 and 3 ( and graphs 2 and 4) are similarly shaped with peaks and valleys occurring at approximately the same X values. I suspect that's because the measurements are made 40 mm apart on the Y axis (a full rotation of the drive pulleys) which represents one full rotation of the drive pulleys. Doh! It might have been more interesting if I had made the measurements maybe 25 or 30 mm apart instead of 40.

It's hard to say what this means for print quality. The most obvious effect should be waves in the X parallel surfaces of prints, with peaks spaced 40 mm apart. I can't say I've ever seen that in a print, but I never really looked for it. The fact that the magnitudes of the waves changes as a function of Y means that X parallel walls of prints at different Y ordinates will be slightly different. But can you see it or measure it? Of course, every surface printed will have some waviness as a result of off-center drilled drive pulleys.

Someone on a forum suggested that the waves might come from out of round idler pulleys. In UMMD the idlers are made from F608 bearings, 22 mm in diameter. If one of those was out of round I would expect the waves in the graph to show up with a period of 22xpi=69.1 mm. I can't see any 69.1 mm waves in the graphs, but maybe they are masked by the waves from the drive pulleys. There are 8 idler pulleys that turn when the carriage moves in X, so unless one of them was really bad, I'd expect any errors in roundness of those pulleys to show up as noise in the measurements.

I think I'm going to invest in some better drive pulleys and run the tests again, this time with the Y positions not 40 mm apart.

Here's the raw data that went into the charts.