Every time you buy a VEX 393 motor, it comes with a little plastic packet of doo-dads whose function is not immediately apparent. These items are called shaft couplers and are TOTALLY OPTIONAL for you to use.
Why do shaft couplers exist?
First, a teeny bit of history: The motors they had *before* the 393 motor had a little plastic piece (called a clutch) sticking out from where the shaft gets inserted, making it essentially level with the screw holes. The current 393 servos still do have this external clutch, as shown in the image below:
Now when they switched from the old motors to the more-powerful 393 motors, if people wanted to swap out motors on an existing robot, all of a sudden they had shafts that were about 1/2″ too short!
Enter the shaft coupler! The shaft coupler is a cylinder and teeny tiny stub of a shaft (see image at the top of this post) that together act as an “extension cord” to make the 393 motors fit onto robots with the older, external-clutch motors.
So why do they still ship these with the 393 motors, when the older motors have been discontinued for quite some time? Well, there are still probably some older motors floating around out there, and the servos do still have the external green clutch, so … old habits die hard?? The RobotMesh (West Coast VEX reseller) has this on their product page. Not sure how much I agree with it, but here you go.
Makes replacing 3-Wire Motors quick and simple.
Placement between motor and drive shaft makes changing shafts easier.
What do I do with them?
If you’re like me, you probably have a LOT of shaft couplers floating around your lab. Why keep them? When would you ever want to use them?
Convenience. They still do come in handy as “extension cords” for when you’ve got a shaft that’s not *quite* long enough, and you’d rather not cut down a new 12″ shaft. Take ’em or leave ’em, but don’t worry that you’re missing out on something important if you skip them.