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Unread 24-02-2014, 09:12
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Rob Stehlik Rob Stehlik is offline
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FRC #0610 (Coyotes)
Team Role: Engineer
 
Join Date: Sep 2009
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Location: Toronto
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Re: Baxter Bomb Squad 2014 ~ Nighthawk

Quote:
Originally Posted by JTN View Post
The reason I said the original design of the cams earlier in the post was because we added one slight notch on each side that allowed the catapult to rest slightly when cocked to lessen the stress on the van door motors. We actually learned that it was possible to remove those two motors entirely (the 775s were doing all the work anyway) and the small notches prevent any possibility of back-driving.
-John Taylor Novak
Nice to see another cam based catapult! We came up with a different solution to back driving that you may be interested in: The final 30 degrees of our cam profile is circular, so there is no reaction torque from the catapult springs. Once the cam follower gets to the circular part of the cam, there is no chance of back driving.



As a side note, we built a small cam driven catapult last year for a non FRC project, and experimented with a notch in the cam to prevent back driving. It worked, but we found there to be a large current spike when the motor was trying to get the follower out of the notch.