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Unread 01-12-2011, 00:05
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Re: Gearing for 20 FPS?

Frankly, the easiest way to reach >= 20 FPS is, besides throwing on more motors, NOT approach the 120lb weight limit (which, when adding in the bumpers and battery, goes to the limit of about 150 lbs). Since F=MA, and V=int(A(t),t), Shaving 20 or 30 pounds would be a huge boost in acceleration, and thus make it possible to reach those speeds within the length of the field.
Taking our 2011 robot as an example, it only had sprockets+CIMple boxes as a reduction, while weighing about 110 pounds competition-ready, it accelerated faster to higher speeds than our similar robots in the past that hit the 150 pound mark, but had higher reductions to get similar acceleration up to their lower max speed.
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Unread 01-12-2011, 00:13
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Re: Gearing for 20 FPS?

If you open up the question to bots that are geared fps free speed, it's not terribly uncommon. Our 2011 comp bot had a free speed of 20.6 fps, and our 2011 prototype Emperor Swerve was geared for 20.7 fps.

Frictional losses obviously bring these numbers down.

Both these robots have shifting to provide a low gear, and our comp bot was somewhat underweight and had very little friction in drive.

Using the oldschool version of JVN's design calc with the drive modeling tab allows you to graph the position and it's derivatives over time, and study what changing mass, friction, power, gear ratio, etc... has on them. It's very interesting how a *slight* friction difference can change speed appreciably.
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