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Pins?
badbrad, Moshingkow, and ReggieB,
Are the locking pins IN or OUT of your gearboxes?
I have not personally looked at this year's drill motor and gearbox, nor the FIRST provided mounts. My comments are based only on 6 year's experience with the units provided in last year's kit.
I think that leaving the pins in is extremely risky, and an invitation to breakage. When the driver backs off the stick with the robot at speed and its momentum overruns the drill transmission output shaft, the shaft locks to the transmission housing. Whatever mounts the housing to the frame is immediately shock loaded with a torque equal to the torqe it takes to spin your wheels.
Shock loading sucks. It's a leading cause of mechanical failure. The people who developed the transmission, with its locking pins, developed them to take the torque loading involved when you tighten or loosen a drill bit in a keyless chuck, while you hold the chuck by hand. A product that never fails when operated in that mode can't be expected to absorb the kind of shock loading produced by a FIRST bot drive without failures.
BTW, this problem is most severe if the transmission is run in low range with direct drive. If there is a stage of gear or chain reduction between the transmission and the wheels, that reduces the magnitude of the shock loading by the gear ratio.
I think the teams who counsel leaving the pins in for their braking effect have used drive train designs and control strategies in the past that mitigate the shock loading problem sufficiently to escape damage. They have been lucky.
So do tell, gents. Are you running pins IN or pins OUT while observing these problems you are describing?
Dodd
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