Thursday, September 28, 2017

This Is What Can You Do With a 3D Printer, No. 1

Here's a project I did about 11 years ago, years before I built my first 3D printer.  It's a Van De Graaff generator (VDG) that produces about 400 kV (that's enough to thrown painful sparks about 300 mm in dry air!).

I never liked the look of the wood box on the bottom, and it was all a little heavy, so a few months ago I decided to update the design.

I redesigned the base and rollers to be 3D printable and found a small DC motor that could be mounted on the base without the big wood box.  The rollers use bearings pulled from hard disk drives.  I printed the parts using PLA.

Full details and CAD and STL files are available on Instructables.

I took it to the Milwaukee Maker Faire last week just to show what can be done with a 3D printer, and after it sat unnoticed for a few hours, decided to move it closer to foot traffic and plug it in.  If you ever want to attract kids to a booth at a product show or Maker Faire, just bring along a VDG!  As these people demonstrated a Van De Graaff generator can be a lot of fun!

I suspect this was Kylee's favorite thing at the Maker Faire.  She spent a lot of time with us!

Fun for all!

3D Printed VDG Hurting My Fist from Mark Rehorst on Vimeo.

 In the photos below I used a 30" exposure time and high ISO, then boosted the brightness and contrast to get what you see.  The photos don't quite capture the blue glow that accompanies each big spark.  The big sparks usually look like a thin, bright line surrounded by a pale blue cloud.

Photographing the sparks is a little tricky.  I prefocused the camera with the lights on, then shut off the lights and opened the shutter for 30 seconds.  IRIC, the camera was set to ISO 3200 and f4.  While the shutter was open I walked over to the generator and moved my hand around near it and got the sparks to jump.  That faint purple glow you can see surrounding some of the bigger sparks in the picture is there with every spark.  It just doesn't show up very well in the photos.

3D Printed Van De Graaff Generator with a Plasma Ball Zapping My Hand from Mark Rehorst on Vimeo.

Update 3/8/18

I changed the top terminal from 11" to 14" diameter (still using Ikea Blanda salad bowls) which should allow the generator to hit 520 kV.  It now discharges continuously from the top terminal to the brush on the bottom of the machine, so I slid one of the original 11" bowls down the tube to cover the bottom of the generator and this is what it did:

The distance from the top bowl bottom edge to the bottom bowl top edge is 550 mm.

I still have some optimizing to do- the sharp edges of the bowls have no insulation, so they tend to create corona discharge.  I'll probably get another 14" bowl for the bottom, and maybe a longer piece of pipe...

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