vandegraff

This little frog prince was found in the garden section at Fred Meyer. The ball he's holding is stainless steel and much rounder then anything else I've considered for a torrid before. They gave it to me for half off because the crown is busted. This brings the total cost of the project to $7 so far. The Torrid has about a 9.5cm diameter putting it close to a 30cm circumference. This will give us a good charge with very little leakage.

The Belt, Rollers, and Brushes

Probably the most important part of making a Van de Graff is the selection of the materials for the belt and rollers. For the rollers you want two materials that are as far apart from each other as they can be on the triboelectric series. You also want a slight hump in the middle of the roller that tapers off on the ends. This gives us a good barrel shape that will keep our belt from falling off of the roller. For the top roller most people choose Nylon as it is resilient, easy to shape, is high on the triboelectric series and can usually be picked up for about a buck at any medical supply company. For our project we will be trying out an assortment of glass beads.

I chose beads because glass is slightly higher on the tribo series then nylon, I have no medical supply company near me but there is an unusually high demand for glass beads where I live, they were cheap, already in the right shape, and unlike the glass fuses I was using before they aren't likely to break so easily. I've tested spinning them with a belt much faster then I will ever need to on the Van de Graff and they held up just fine.

For our bottom roller we'll start out with silicon. It's low on the tribo series, I've had good results with it before, it's easy to both come by and make into our barrel shape if you buy it in tape form.

Our belt will be rubber (not black) and we'll test out a variety of rubber bands, cut up balloons, and possibly surgical tubing.

The Motor

This motor I salvaged from a 7 Volt Dewalt drill. It is a Mabuchi RS-550PF that takes 6-15 Volts at 1.4 Amps. It makes about 6500 RPM with a shaft diameter and length of .13cm and .44cm respectivly. It has a torque rating of 44.1 g-cm and it's nominal operating voltage is 12 V. In case you don't have an old Dewalt to butcher, you can buy one from Jameco for $3.29. If your making 100 Van de Graffs you can get these little suckers for just $2.69 each! The Jameco part number is 153656CC

The Support Column

The Support Column is the second most visible Part to our VDG. We don't want it too fat as that would take away from the magnificence of our well chosen torrid. At the same time we want it to be roomy enough for us to comfortibly fit a 1.5cm wide rubberband in there without it rubbing along the walls. For this we will use 1 or 1.5 inch PVC.... What's that you say, earlier I was complaining about the unsightly, eye pain inducing offences that is Polyvinyl Chloride?

.... Yes well, we're over that... for now. It's cheap, I'm married, in college and I don't know how I can justify to my wife that I just dropped 27-40 bucks on 10 feet of clear PVC when we are only going to be using about a foot and a half of it. (Not to mention one or two couplings to make mounting and removal easier)

Thats right people I said CLEAR PVC as in 'see-through.' Not only is clear PVC more asthetically pleasing then regular PVC but it allows us to see how the thing actually works! What you can't see can kill you. Listening to the Van de Graff build up it's charge is only so intimidating. Seeing that the source of your 'don't shock me again' fears is in all actuality a spinning rubberband just might appease my friends senses of adventure just enough for them to zap themselves with this little device one more time. Oh we can only hope....

Anyway... as was mentioned clear PVC aint cheap, and I am, so for now regular PVC will have to do. **sigh** When we get a few more bucks in our pocket, or until someone generously donates [I am willing to advertise :)] clear PVC to our cause we'll use that, but for now we'll settle on regular PVC.

The Base

As yet unselected, now I regret throwing out those old computer power supplies. We'll use a vice for now, and come up with something better latter.

Power

Ditto to the above section, but we'll be using a variety of power cube transformers until I have the time and make the effort to come up with something better.

Putting it all together:

To begin construction on our VDG we'll cut a hole in the bottom of the torrid so that we can mount it on the PVC shaft. I'm still not sure if I prefer 1 or 1.5 inch PVC so we'll walk on the safe side and cut a 1/2 inch hole (cuz it's what I have).

With a sharpie trace the PVC pipes rim on the spot you want to cut and go to town with your favorite high speed rotary tool. I used 2 bits, a cutter for the vast majority of the hole and I did the fine detail arround the edges with a grinding bit. Use protective eyewear and possibly some sort of ear protection. By no means was this a quite task and my ears were ringing half and hour after I was done.

Check to make sure the pipe fits, mount it up and take a picture!

The PVC we chose as a support colum measures 1 foot in length and is 1.5 inches in diameter. There is a bevel at one side and a small lip at the other. This lip will make it easier to mount to our base later on. Because the hole we cut in the torrid is only half an inch in diameter and I don't want to widen it (now anyway) we will be using a 1inch to 1/2 inch PVC adapter. The reason being the 1 inch adapter fits inside of the 1.5 inch PVC stem we're using, but it doesn't fall all the way into the PVC because it too has a small lip along its edge.

Because the rubberband we're using measures **inches** it won't reach the entire length of the PVC. To help with this length problem, without shortening our PVC, we will use a variety of connectors to lower the top roller so it reaches about 3 inches from the top of our support column as is shown in the following illustration.

The upper roller is on a nail shaft as was done over at scitoys. The shaft is inseted through 2 small holes drilled opposite each other in a 1inch PVC connector. The connectors top end is attached to a few inches of PVC and then to the adapter.

For the lower roller we are going to drill a 1/16 inch hole in the PVC about 2 inches from the bottom. A nail can be used as the shaft of the roller, but we're using a shaft taken from a ripped apart toy. inserting it and attaching some clips (gears in this case) to the ends of the shaft will secure it in place. The bottom roller will be added later.

Now we move onto the upper brush assembly. I've decided to use one of those metal strips that are on the end of box tape dispensers. My wife was asking why I was taking a picture of the metal strip with a penny. I do this to give you an idea of size, she liked the idea, but decided it needed some form of garnish hence the broccoli.

The reason that I chose this is that it's already got a bunch of sharp tips percetly aligned with each other. If it doesn't work out that great we'll probably end up soldering a bunch of pins together or some other typ of modification.

I ended up cutting the strip in half and soldering the top edges together. To make sure the holes were aligned perfectly I inserted a nail through the holes while I soldered. This gave me 2 rows of sharp points and 4 holes to mount the brush with. The rows are about 1cm apart from each other. Cutting 4 holes in our PVC adapter then inserting a nail through each hole in the PVC and through our brush holes allows us to slide and position it so that we can get the best ion pickup from the upper part of our belt.