As in most FRC designs, a plethora of mechanisms are used by teams. In most successful cases, the motor is not moved during a release. My team used a dog gear system to disengage from the gearbox in 08, similar to the AndyMark shifters. I would recommend taking a look at some drawings on AndyMark.biz and figuring them out.
I have also seen gate hinges and... a hood latch... used to release cables with varying success (usually good if you don't dip 'em in paint

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