19 years ago
1- A set of coils causes a mechanism to clamp onto the ribbon. 2- Once clamped, a second set of coils is energized and moves the clamp (and ribbon) a very small amount. 3- At the end of the motion, a new clamp secures the ribbon at the new position 4- The first clamp releases and is moved to the original position 5- The process is repeated.
It's a microstepping motor.
Well, the first problem is that the power you'll be able to generate is proportional to the strength of the magnitic field. This, in turn, is related to how much iron you have. If designing a DC motor that's one of the limiting factors. Bigger magnets don't get you more power without more iron. If you are not going to have any magnets then the field strength has to be generated by burning energy, which is not very efficient at all.
I like high performance DC motors. If properly designed and operated they can run at efficiencies apporaching 90%. That's pretty good. Still, if you'll need, say, 5000W to run a robot full of motors, that means that you will be burning, at the very least, 500W in wasted energy. The number is probably many times worst due to the fact that all the other elements involved will not operate at 100%.
Here's the funny thing. The mechanism you are proposing is almost exactly how motion picture cameras work. Of course, this is done off a single motor and using sprockets. The film is clamped between two plates. Claws engage the film's sprockets. The clamp is released. The claws pull the film down the the next frame. The clamps are activated again. This happens over and over again at whatever frame rate the rig is being operated at. Lookup "Geneva mechanism" on the web. I would suspect that this approach (meaning, a single DC motor with some mechanics) is much, much more efficient than what you are proposing. Efficient in terms of energy in -> energy out.
On a different end of the scale, ultrasonic motors can be thought of operating on a very similar principle. I think they are really inneficient though. Years ago I heard that a consumer camera (Cannon) used an ultrasonic ring to actuate focus on the lens.
I do think that the secret is in small motions. Magnetics gets interesting as the air gap is reduced. The biggest challenge yet might be that of manufacturing something like this that can run these clamp-pull-move-clamp-reset cycles at thousands of times per second and last.
I look forwards to seeing what you are going to post. Do you have any video of a prototype in opeartion?