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Originally Posted by Mr. B
Thanks to the Build Blitz team! Just watched the Elevator Video/Blog on the Build Blitz Blog page. Can someone tell me how the elevator will hold the totes elevated? ( what will keep the gearbox from back driving) Thanks in Advance
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We're working on prototyping and testing several different applications of these linear elevator parts. Having a mechanism that can backdrive is not necessarily undesirable, but what most people mean when they discuss backdriving in terms of arms or elevators in FRC is when the mechanism falls due to gravity after the operator controls are released.
To help prevent this form of "backdriving", there are several ways to accomplish this, including using the built in PID functions in the FRC code library to hold the elevator at it's current position. This, combined with gearing the elevator such that the stall current at the motor is minimal (e.g. won't smoke a motor) and adding constant force springs to help counterbalance the weight, will help make a fast and responsive linear motion system.
The current iteration of our elevator prototype is geared to quickly pickup totes (<1 second to bottom stack) with a single BAG Motor and 2-stage VersaPlanetary gearbox, while the motor remains at 25% of stall current with an elevator load (carriage + tote weight) of 60lbs. This is without any constant force springs to help counter-balance the system.
For implementing PID controls, I've had good success previously (most recently in 2011 when I was on 228) using Sharp IR distance sensors for elevator height control. For this, it was as simple as mounting the sensor on the robot chassis looking up at the elevator carriage to measure the height of the elevator.