Remote Control Conservation of Angular Momentum Device

remote control angular momentum deviceSo, yes, that’s quite a title.  As mentioned in a previous article, the cheap RC truck is a great source of components for whatever hack or re-purposing you have in mind.

The first thing I tried with this set of components was a very simple hack.  I don’t remember all the details, but at some point in my education as a mechanical engineer I learned about conservation of angular momentum.  In two dimensions, it’s pretty simple; if something is rotating, angular momentum has to be maintained if there are no external influences.  With an external influence – like a motor changing direction of a rotating mass, you should be able to make something else move.  In the three dimensional world that we live in, if this rotating mass is in plane with a central axis, you should be able to get the whole deal to spin.  If it’s out of plane as shown above, I’m not really sure what happens.

central axis made out of a "pro dirt" wheel and a nailThis concept of 3D conservation of angular momentum did give me an idea for making something move about a central axis.  If one has a motor on either side of a central axis and the motors are started from rest, the whole device should rotate one way or the other to compensate (it would do this if it was in plane at least).  Using the motors, remote control, and wheels from the RC car that I recently took apart, as well as a piece of tw0 by four and a nails, I was able to give this concept a try with the masses out of plane.

One wheel was used with a nail to form a central axis that the device could balance on.  Two other wheels were put on the end of each motor to form a rotating mass.  Two 3/4 inch holes were drilled to stick the motors into.  These motors are fragile, so they will break if forced in too much.  The middle was milled out to accommodate the motor’s leads.  A very crude design, but good enough for a proof-of-concept.

After this was done, the only thing left to do was try it out.  I was concerned that the “rotating mass” or recycled wheels wouldn’t be heavy enough to affect the whole assembly.  Anyway, here’s the results, they should speak for themselves:

This might be a good science project, although I’m unsure about the plane used for the rotating masses.  If you were to rotate both motors so the rotating masses were parallel to the floor, things would be much more straightforward.  Either way, it would probably be easier to just collect some leaves or something.  I did end up doing a more developed version of this that was actually able to roll around on the floor, so if you liked this post, you’ll want to check that out.

If someone has a good explanation for what is going on, feel free to leave a comment!



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