
21-03-2008, 18:16
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human
AKA: Colin Nobles
 FRC #0148
Team Role: Teacher
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Join Date: May 2005
Rookie Year: 2005
Location: rochester
Posts: 432
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Re: DC Motor and Gearing
Quote:
Originally Posted by Don Rotolo
Yes in theory, but in practical terms it's not a big enough motor.
Gears: A 5 tooth gear is too few teeth. To get reduction you need compound gears. Try 10 tooth against 40 tooth, on the same axle (i.e., stacked against each other co-axially) as the 40 tooth another 10 tooth, then driving another 40 tooth, which is the final output. If it needs to be further, another 40 tooth would be used.
OK, torque: If you need maybe 400 just to overcome friction, that leaves a peak of 230-ish to do the work, and that's at stall. With the motor moving the actual torque will be much less - it IS linear, so with X as the speed axis (0 to 16000) and Y as the torque axis (0 to 78.7), draw a straight line from (16000, 0) to (0, 78.7) - that is your torque line. You can see that there's not much torque available at 16000 RPM, and the motor will slow down until the torque is enough to drive the load.
Overcoming that constant 400 oz-in of torque required to start the shaft moving is a considerable challenge, particularly for 2000 RPM and the small (=affordable) motor world.
If you can provide us more info on the application, we can brainstorm some possible solutions.
Don
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good call don yeah a 5 tooth gear is really small good call
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