The Alternate Scientist

Building the TOMI-2 Linear Permanent Magnet Motor


"If you were going to rob Radio Shack," said Mike, "couldn't you at least have got me some stereo speakers?"

"I ordered these from radioshack.com last week and they just arrived.

"Are you going to start a magnet store?" he exclaimed. "You have hundreds of magnets here!"

"I only have one pack of five number 64-1888 round ceramic magnets and seventeen packs of five number 64-1879 rectangular ceramic magnets," I corrected him.

"Oh, is that all," he said mildly, then demanded, "What are you going to do with them?"

"I am going to build a TOMI-2 as described by Ken Hickman on KeelyNet. I leaned over the computer keyboard and follwed a bookmark and a few links to bring up the page.

Mike sat down and read for a minute. "Hey, that's pretty neat. Does it work?"

"That's what I want to find out. And he doesn't say whether the roller shoots out the end or comes to a stop. So give me a hand building it and we'll see," I said leading him to the main part of the basement.

An hour later we had a length of plywood with grooves in it to hold two one-foot long strips of plexiglass 3/4 inch apart. We also had a dozen pieces of 1/4 inch thick plexiglass slightly smaller than the rectangular magnets and two strips of wood to block the magnets in place.

We went back to the electronic bench and assembled the parts according to the drawing still on the seventeen inch monitor.

"It's not very pretty but let's see if it works," I said separating three of the round magnets from the stack to make the roller. I placed it in the guide and began to roll it toward the stationary magnets. Suddenly it jumped from my fingers and locked itself between the near poles of the stationary magnets.

"That doesn't seem right," I said walking over to the computer. "Oh, I see. I have the rolling magnet attracted to to the first stationary magnet. It should be repelling."

I pulled the roller free, turned it end for end and placed it back in the guide. "It's fighting me now," I told Mike as I pushed it with my finger. Then, as it entered the first stationary magnets, it shot from my finger again but passed all the way through the device this time and a couple inches out the other end. Then it jerked back, as if on elastic and locked itself between the far end poles.

"Wow!" said Mike. "That moves fast! Can I try it?"

"Yes you may," I said retrieving the roller and handing it to him.

He put it in the guide and began to roll it. "It does fight you doesn't it?" he said.

Then, "Wow!" again as it suddenly shot through the stationary magnets bouncing back once more to remain locked at the end.

He did again. And again. And again. "Would it work if it were longer?"

I don't have any more magnets," I told him. 'but let's find out in a roundabout way." I removed all the stationary magnets except the first two sets of six. "Now try it," I told him.

He did and the roller shot quickley through the abbreviated TOMI-2 and locked into place at the end. I returned two sets of magnets. The roller zipped through the two and locked at the new end. It did the same with three, four, five, six and finally the original seven sets of stationary magnets.

"OK. You've convinced me," Mike relented. "It looks like it will work for as long as we want to make it."

"I don't see why not," I said.

Mike thought for a second. "Could we make it long enough to curve around to connect the end to the begining?"

"That is exactly what Mr. Hickman talked about doing. I, for one, can't afford that many magnets nor do I have the tools to fashion a smooth circular track. I asked him by email if he got it to work. He told me that he hasn't been able to get the roller to go all the way around the circle yet.

"Is there anything else we can do with it?" Mike asked running it again and again.

"Does the moving magnet have to roll?" I wondered. "I have and idea. Try this instead of the round magnets." I picked up four spare rectanglar magnets, put them in a stack and handed it to Mike.

He put the stack in the guide and pushed it toward the stationary magnets. "It's just as hard to get started," he said. "Whoops, there it goes." The stack of rectangular magnets shot through the TOMI-2 and bounced back to the end exactly as the round magnets had.

"That worked," said Mike excitedly.

"I can't say that I expected it to. I thought at least that friction would slow it down and stop it in the middle. That makes me wonder if the round magnets accelerate so fast that they don't have time to roll.

Mike tried the round magnet stack again then the rectangular one. "It's hard to tell the difference. You might be right," he observed. "Or maybe the rectangular one is lifting off the wood."

I reached over and pressed on the top of the now end-locked rectanglar magnets. They moved about an eighth of an inch before touching the wood. "I think you are right," I agreed.

He ran the round magnets again then pressed down on them as I had. "This one is definitely touching the wood," he announced. "Anything else we can try?"

"Well, I had hoped the roller would shoot out the end so it could coast back to the beginning on a circular track to save money on magnets. But I didn't expect it so I'm not disappointed. Well, not much anyway."

"Could we do something to make it shoot out?" Mike wondered.

"Let's try spreading the magnets farther apart at the exit so there won't be as much force to pull the roller back in." I tore a flap off an old cardboard box and, using a paper cutter, cut a half dozen 3/4 inch by 1 1/4 inch strips. I used then to space out the last two paired sets of magnets into a shallow 'V'.

Mike pushed the roller into the TOMI-2 again. It shot in as before but instead of stopping at the end, it rolled lazily out and onto the workbench. "That did it," he observed.

"Yes, but it certainly doesn't have enough momentum to roll around to the beginning," I said disappointedly.

"It's a start. Remember, the dome wasn't built with a ray," Mike commented sagely.

I just groaned.


A few days later Mike bounced in the door of my basement workshop and began playing with the TOMI-2 as he had done on every visit for the past couple days. As I was closing the door behind him he said, "It sure is hard to get this roller started. It's kind of like compressing a spring."

"Let me try that once," I told him taking the roller and sliding it into the track. I pushed and released, pushed and released. Finally I admitted, "You are exactly right. It does feel like a spring. Hmmm. I wonder if that compressed 'spring' provides the energy to drive the roller through the TOMI-2?"

"How could we find out?" questioned Mike.

"Well, let's think a minute... It's obvious that the springiness is caused by the roller being resisted by the reverse poles of the first stationary magnets." I considered it for a few seconds. "I know, let's start the roller from inside the stationary magnets."

I placed the roller at the gap between the second and third sets of magnets. It promply found a rest position and stayed there. I pushed it gently with my finger, expecting it to shoot through the rest of the magnets. It did not. It eventually jumped to the gap between the third and fourth sets of magnets and locked in place there.

I pushed it gently again and it jumped to the end of the fourth set of magnets. As I kept pushing it jumped to the end of the fifth and then it took the sixth and seventh the sets in one jump.

Mike repeated my experiment. "It feels like a much smaller 'spring' and the roller travels a much smaller distance," he observed accurately. "So, what does that prove?"

"It is a strong indication that I was right," I said dejectedly. "That it is the hard push you have to give the roller at the start that provides the energy to drive the it to the end. And if you extend the track into a circle you will have the situation we just created in miniature. You will always be trying to start the roller somewhere in the middle of the track and it will take a only little jump and then stop."

Mike considered that. "So we can't make a circular one that will run forever?"

"I really don't think so," I responded sadly. "But I know Mr. Hickman won't agree with me and I would like nothing better than for him to prove me wrong!.


Tom Hunter (N3CRK), 02 DEC 2000