Fixing Slop of Gear on Hex Shaft

[MichaelBick]

If possible, you should bolt the gear directly to the arm while putting your encoder on the last stage pinion. This will minimize the effect of the slop in the hex bores, while also getting the most accurate arm position.

[ToddF]

There are ways to mechanically reduce the play, like pinning the connection, shimming, and the like. However, one thing that works rather well is preloading the connection with a counterbalance spring. We do this quite often by using surgical tubing to partially support the weight of various arms. It has the added benefit of often reducing the size of the actuator needed to provide the motion.

But, if you really want to do it mechanically, use a couple #4-40 screws and attach a hex shaft collar to the face of your sprocket. Position the sprocket with the collar loose, then tighten it up. (Disclaimer: never actually done this, but seems like it ought to work.)

[FrankJ]

I like Todd's idea better that this, but you could bearing retaining compound. The downside is you will not dissemble your mechanism without heat and maybe a press.

Controls wise: maybe a deadband and keep the D term small or zero.