Van De Graaff generator and legos.

[Vepsu]

Umhh.. I'm a pretty newbie on this.. But I'm trying to build a working Vandegraaf generator from legos.
So, the basic idea is that I build high pipe from legos, and then use lego-motor which makes two rods rotate. The second rod is on the top and the second one is on the bottom. They're covered by lego-car-tires (something soft-rubber/plastic) and a belt runs with them as the rods rotate.

Then there is two combs, made by foil, both near the rods and tires. One on thr top and other one on the bottom. Then there is foil sphere on top of that thing. So.. Umhh.. And the bottom comb is connected to the ground.
Could this thing really work? And what I should use as belt? And are the rods (rollers) and combs ok?


Picture of it:

       _____
      /     \
     |       | Sphere
      \_____/
       | % |
      -|=#=|-    Upper rod/tires
       | # |
       | # |     #=belt
       | # |     %=comb
Motor  | # |
 |__|--|=#=|-    Lower rod/tires, with motor
       | % |
-------------------------

 

[arcnets]

Hi Vepsu,
I think your design won't work because it doesn't have any parts that can produce electric charge.
Apart from the 2 rollers that hold the belt, you need a 3rd roller which touches the belt from the outside, close to the bottom. This must constantly be charged by rubbing against a stationary object which is grounded.
It is very important to chose the right substances for the 3rd roller and the 'rubbing agent'. You should try many substances until you find a combination which produces static electricity very reliably, even under slightly moist air conditions. My personal favorite is plexi glass (PMMA) plus fur. Always works well when I rub them, but I've never tried them in any motor-driven device. I guess pressure must not be too high but speed must.
The second important point is insulation. I'm not sure if the lego wheels & bearings provide a well-enough insulation, preventing the charge from jumping over. You could test this by building a prototype, and charging up the foil sphere from an external source. See if it holds the charge!
BTW, legos are made of ABS (acrylamide-butadiene-styrol) which is a substance optimized for surface gloss and mechanical strength, but not necessarily for insulation. Maybe legos are after all too hydrophile to provide a good HV insulation. Try it!

There are some websites on how to build your own Van Der Graaff, maybe a google search will help.

 

[Vepsu]

Thanks a lot Arcnets! Maybe this will help me a bit.. :p

I already have other materials beside legos, but I will try with legos first. (They are easy and fun to deal with ;)

I already managed to produce some pathetic sparks with it (I changed some thingies a little..)
I'll try your tips.. I hope it works better.. :)

Edit:

Actually it works now.. :p It produces sparks which travel about 10mm. Pretty pathetic still. Needs some tuning.

I used artificial leather as the belt and the upper roller is alumium foil covered, as the lower is covered with electric tape.
I have to try that fur later..

 

[Vepsu]

Working

Now the Van de graaff generator works reliable, though it isn't very powerful, but it charges fast. Maybe the sphere isn't the best possible. It is just a foil covered plastic cup, upper roller is from nylon and lower is from PVC. The belt is made from slices of rubber gloves.

With aid of few Leyden Jars, it produces now over 10 cm (~4 inches) sparks. (For now, I'll try more longer ones later.)

 

[arcnets]

Congrats, Vepsu!