Quote:
Originally posted by dddriveman
What is a left-handed screw? I only have limited knowledge? Is it like the stops that they gave us in the kit? I put the drive tran together exactly like the plans on the FIRST website.(www.usfirst.org) THe plans for it are under team resources>documents>drivetran closeup. GIve or take a few change like I didn't put on the locking rings. The driveshaft is the 3/8 keyed axle that they gave us.
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A left-handed screw is threaded such that it tightens and loosens by being turned in the direction opposite of regular screws.
Righty-tighty, lefty-loosey, y'know? Well, left-handed screws are just the opposite.
The outside of the drill output shaft is a normal thread, so spinning something to the right over that thread would tighten it.
Inside that output is a small center-bored hole. The inside of that hole has a left-handed thread.
If it takes less force for the motor to unscrew itself from the shaft coupling than it would for the motor to move the robot, it'd unscrew. Imagine the motion you'd make when you screwed it all together. Now, imagine that your hand is replaced by the motor. See how it's the same thing?
Well, by putting a left-handed thread and right-handed thread together, it makes that unscrewing impossible. For as long as they're spinning together, one screw is always trying to tighten itself while the other tries to unscrew. They keep each other in equilibrium, meaning that most of the energy output by your motor goes to the wheels -- not to taking apart your drivetrain.
If you didn't put the left-handed screw in, you'd find that the motor was unscrewing itself from the coupling, especially in pushing matches. Since everything is locked in place and the force isn't going toward making your wheels spin, something, somewhere, will break.
Similarly to the left-handed screw, and as Ken mentioned, a pin through the shafts ensures that they always rotate together and is another every effective method for keeping things from breaking. Just be sure to use the proper diameter pin to withstand the forces in the system.
(See what engineers can do for you?)