The Bosch drill motor gearboxes have a mechanism that is making me curious, and I’d like to use it on a robot. This mechanism allows the main axle to free-spin during normal operation, but locks up the shaft when the motor stops powering. My team has removed some critical pieces of this mechanism (cause we don’t want the robots to drive like that), but I’ve never figured out how it works. Does anybody know how this works? I could use some diagrams, or good explainations. The other question is, does anybody know if there are Intellectual Property/Patent issues if I copy this mechanism for a robot?
the anti-Backdrive pins
they are 2 small cylenders in the linkage between the output shaft and the clutch they act as a sprag when torque is applied through the shaft and dont act at all when torque is applied from the gearbos, actualy in normal operation they kinda jiggle a bit in there. they are arranded so the output is coaxial and on the inside of the input witch is basicaly 4 Oblong pin type things the output shaft is keyed to a piect that mates with thoes 4 poker things with is part of the fianl planetary gearset of the transmition when you put those pieces togeather the mate takes up two spaces between the 4 pokers off the gearset there are 2 extra spaces. thats where the anti backdrive pins go . then torque is applied in the opposite direction (from the ootput shaft) the shape of the oblong poker thingies forces the pins to grab the outer steel cacing around the tiny asembly stopping the unit from backdriving.
if you google search Sprag Clutch or a combination of ~ anti-back-drive sorag clutch and dual engine helicopter gearboxes~ you can find more information. sadly enough The millatary dosent release too much info about their helicopters gearboxes
To learn about that, I just took apart one of the gearboxes. The more afraid you are or screwing it up, the more you will learn. 
If that’s not your type of thing, check out this PowerPoint presentation which basically takes apart a Bosch gearbox for you. http://www2.usfirst.org/2004comp/Specs/Bosch_Disassembly.ppt