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We have used planetary drives for 2001, 2002. Mainly to show off machining ability and for compactness/weight reduction.
However, planetary, worm&gear, bevel gears, and the helical gears in the kit this year, have reduced efficiency for a given gear ratio than the good, old fashioned, easy to fabricate spur gear train. I forgot sprocket and chain, but that's less efficient as well.
Given the limitations on current (due to fuses) and the motor size, gear box mechanical efficiency may be the most important consideration in drive system design.
The energy per motor limitation is the other reason why you want to get four motors into your drive system somehow. If you try to go up to six motors, you may discover that you have put too much weight and resources into your drive system and you cannot do anything else. But, I haven't got any experience with that.
One advantage to being a torquier bot than a speedier bot is that you end up drawing less available energy out of the battery per match. Secondly, with a crowded field, such as FIRST has provided for the past few years, acceleration is more important than speed. Pushing power is far more important than speed.
We have been bracketing the "ideal" FIRST gear ratio. We started with a 15 fps bot, which was hard to control and couldn't run very long on one battery, to a 4 fps bot which runs forever on one battery. We also have a 6 fps bot with an inefficient drive system. This guy is better than the 15 fps bot at battery life but can only handle about 15 minutes of hard driving before you can smell the motors.
This year's bot was a 4.1 fps with four drive motors. I think we can go as high as 5 fps with the four motor version. We had no trouble with motor heating, battery drain, motor damage, etc.
I actually took a page from Wild Stang's 2001 robot (which they were gracious enough to show me) for our gear boxes this year. So, thanks for the tip!
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