It's off-topic, but I wonder if anyone here has got any sound experience of using friction brakes to accurately control the torque on a small continuously driven rotor.
The application is a bit like a drum brake on a car, but it runs continuously and needs to give very consistent friction levels over long periods of time, independent of rotational speed. In a way, it's a bit like a miniature dynamometer.
Regards, John H
Use a DC motor running as a generator as your brake. Wire the motor to a variable rheostat and you'll have very accurate control of the resistance offered. If you can afford to use a more sophisticated approach you can use MOSFET's and digital control to present a load to the motor-generator. This allows precise digitally controlled torque. Be sure to heat-sink adequately.
-Martin
The unit is going to be built by the thousand for $50 cost price each, so that sort of approach is not feasible. There is a competitor's unit which occupies a niche of the market, selling for $1000 each which uses a servo motor with closed loop control, but most customers can't afford it.
John H
What power level are we talking about here? Not much if you are going for a $50 MSRP.
-Martin
Have you looked at switched reluctance motors.
It's for individual threadlines in a textile application, maybe 20-40W each.
"John H" a écrit dans le message de news: sf6dnZ8FZfI snipped-for-privacy@bt.com...
A gearbox and a propeller?
"Jean Marc" wrote
....speed dependent....
John
No problem.
The continously driver rotor you mention in your original post, is this driven by a larger DC motor? How fast?
Funny enough, I have bit of a background in the textile industry as my parents were in it when I as a kid. I'm not anywhere near that industry now.
The problem with your brake-based torque control is that too many variables are involved in order to make it work reliably and consistently. You didn't say what degree of accuracy, stability, repeatability, etc. you expect to deliver for $50.
If you can do this electronically $50 is not a horrible budget. Mechanically? Well, it depends on a great many variables.
-Martin
The motor isn't a bad approach and if the application only requires very small motors, (ie.one per thread) this may not be as expensive as one may think. Otherwise, I have seen cardboard spools used with adjustable spring tension fairly successfully in the printing industry. But, small DC motors with individual potentiameters could be as inexpensive as $5 per axis, (estimate with lots of assumptions) and is considerably more elegant.
Edt
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