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Originally Posted by VinceT
Thanks everybody for your help, our robot will be grateful.
But while we're on the subject of friction, we ran some numbers on our previous year's robot, and we've found that our wheels are running about 70% of the free speed RPM that they should. We used the 90 degree box that came in the kit, and I was wondering if this was just our robot's problem or if it was a global problem. Thanks.
Vince T 418
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Part of it may be that the free speed of the motors is not an exact science. The motors will have some variation around the mean. You may have just had low end (but perhaps still within spec) motors.
As to your drive train, 90 degree drives are notoriously inefficient compared to parallel axis drives. This may have been part of it.
Also, your gearboxes require some torque just to drive, even if unloaded. This static torque means that the motors will not reach your no-load spec because they have to overcome this torque even when the robot has reached its top speed.
Joe J.
P.S. on the issue of bushings Vs. bearings, I go for bearing for high speed applications (include wheel axles in this catagory) unless I have a good reason not to (one year, my gearbox was just a whole lot smaller if I just had one shaft with one of its sides a bushing -- so I used a sintered bushing). The choice between bearings vs bushings need not be a religious debate, I balance the pros and cons and make the best choice with the data I have at the time.