I had a thought a while ago that a device could be built with no external moving parts controlled by conservation of angular momentum. Angular momentum is the tendency of an object to stay at rest in a circular direction if no other forces act on it. It’s why a large spinning wheel is hard to stop and why a skater can spin much faster by pulling her arms in. It’s also why you don’t start spontaneously spinning for no reason. However, if, say for instance, you had a large wheel that started to spin very fast because of a motor or other reason, your body would have the tendency to rotate in the other direction. This is the whole premise behind this “vehicle”.
My first experiment with this was a strange and fairly crude object that I called the “angular momentum device”. Although the science behind it was rather dubious, I had hoped to induce a spin about the center axis by spinning the two wheels on the sides. In the video, it seems to work, but I think it was more a matter of vibration. The idea was that something like this could be caused to turn by accelerating both masses in different directions. It didn’t work with the “roller”, and after more thought on this, the “science” behind it doesn’t really make sense. If spun in opposite directions, each wheel’s angular momentum would cancel the other one out. Nonetheless, for some reason, which I’m not sure of, it seems to work:
After this seemingly successful experiment, I still thought some sort of locomotion was possible using angular momentum. After some thought, forwards and backwards seemed likely, but turning less so. So I started building the strange item that you see in the pictures below. This was pretty much thrown together, so I won’t lay out the details right now, but basically it has a PVC pipe frame, masses and wheels that I made with a hole saw out of 1/2 inch plywood, a small radio control receiver, and two motors out of an automatic air freshener – I used the sense-and-spray version as they were cheaper and have similar motors as the other kind. Apparently everything I make these days has air-freshener parts in it somewhere. Update – when this device was made, I didn’t have my Zen Toolworks CNC router at the time, but it would have made the “wheels” much easier to make.
The results of this build were pretty neat. The motors spinning up did cause the device to lurch one way or the other as I had hoped. The device isn’t perfectly balanced, so it tended to start rolling faster when the heavier side was up. This usually meant it was already coming down, so reversing the masses during this condition caused this burst of speed. This looks pretty cool in the video below, so I’m not too disappointed with how it turned out.
One can’t get continuous motion with this device as once the momentum is balanced, it tends to roll to a stop. If, however, the masses weren’t balanced as they are, this may be possible. I milled one end off to make them non-concentric, but so far this hasn’t worked all that well. I believe a better control system is needed for this to work correctly, and probably more weight. Here are the results of what I have so far:
In the video, I put it in a tennis ball container to try to show that it wasn’t powering itself by touching the ground with the masses, although one wheel still sticks out. The goal would be to get a device like this to turn on it’s own as well as go straight, but that would require some clever mechanics to keep everything in the right plane. I think it would actually require another twisting mass parallel to the floor. There is definitely a solution (and I have a few ideas of how to do it), but that is for another post.
Oh and I’m proud to say that, as I own the world’s most advanced tripod mount for the ENV2 phone, I now own what I believe to be the only remote control tennis ball sleeve in the world. Feel free to correct me on this if you own either one.
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