US Digital Shaft Encoder and VersaChassis Hex Shaft

We are running a west coast drive with a WCP DS Gearbox, and as suggested, we attempted to use a 1/4" US Digital shaft encoder on an output VersaChassis hex shaft. However, the hole on the shaft seems slightly too big for the encoder, as the encoder shaft slides in and out of the hole in the hex shaft very easily. There doesn’t seem to be enough friction to move the encoder shaft along with the turns of the hex shaft. What is the correct way to mount these encoders to those hex shafts?

We turn down the end of our hex shaft to 1/4’’ and link the two with surgical tubing and zipties (which work much better and are more robust than any other sort of connection we’ve tried).

What do you mean by turn down the end of your hex shaft?

They used a lathe to reduce the diameter of the shaft.

To “turn” something in this context means to machine it on a lathe.

If your team doesn’t have a lathe, I strongly suggest you invest in one. Even a cheap small hobby lathe (that’s what we use) can do wonders.

Cut a slot in the shaft. Insert the encoder in the oversized hole. Put a shaft collar around it to make the slotted hole compress down on the shaft of the encoder.


We already have 0.251" hole in the VersaChassis shaft (which WCP said was designed for a 1/4" shaft encoder), but that hole is too big, and there isn’t enough friction between the shaft on the encoder and the hole in the VersaChassis shaft to make the encoder shaft turn with the axle.

We’ve reamed some of our own shafts and they’ve came out a little big, we just put some hot glue in there and were g2g. You can do other tricks to make the hole in the shaft work.

A few other options.

We have been using Ruland flexible couplings with the 1/2" shaft on one end and 1/4" shaft on the other.

You could drill and tap a hole for a #10 set screw and then use a set screw to hold the 1/4" shaft tight.

Hot glue works. You can also take a small pocket knife or similar tool and gouge a hefty scratch in the inside of the hole. It should raise a burr just enough to provide a little bit of friction to snugly fit the encoder shaft in there.

You could also try a little piece of scotch double sided tape on the encoder shaft, to take up some of the space.

If you were careful about it, you could probably even use an automatic spring loaded center punch to punch a dimple into the encoder shaft itself, causing it to deform outward a little bit.

I will also note, we typically would not mount encoders of this sort. It’s an over-constraint. We would fit them to the shaft, and then just let them float free, placing a zip tie on the cable, just to prevent the body from rotating.

Could epoxy a 1/4" shaft into the hole in the shaft and the use a piece of 1/4" id hose to attach the the encoder to the drive.

It’d be a lot easier if you told us what resources your team has access to. From the looks of it, it doesn’t seem you have a lathe. Would you happen to have a 3D printer?

A little “goop” works too.
it is a little less sticky than hot melt glue, better option to get it apart if needed.

Drill and tap it, put a shoulder bolt in it, with a little locktight, cut the head off it, and use the surgical tube coupling method, with zip ties.

If your mechanism has significant momentum, and the you get encoder bouncing values when you stop due to the surgical tube twisting, change out the surgical tube with 1/4" high pressure fuel line. We needed to do this last year on our elevator. We have used this method for years in the past with surgical tube, last year was the first we saw and issue with bounce, when changing directions, stopping, etc.

Just wrap the encoder shaft in a little painters tape or scotch tape until it’s a press fit. Single side is fine, you’re not trying to fasten anything just increasing the OD until it goes in smooth. There’s basically no torque transmitted to worry about so this is totally fine. Don’t worry about doing anything more robust than that.

I suggest you use a set of clamps.

I would like to add a warning about hot glue. Only use it on encoders used for speed sensing, if you need to sense position please use a set screw, press fitting or some other method that assures the shafts is locked down. I realize that the OP has specifically said it is for the drive train and thus we can concluded that these are for speed sensing. That said I personally made the mistake of applying that to a hall-effect pot which has lead to some unpleasant failures this year. I hope that no one ever makes the mistake I did.

We have used hot glue to get a good fit in the VersaChassis hex shaft in the past with great results.

This year we hot glued the encoder in the shaft, but ended up breaking one of our encoders (the shaft seized up). Likely due to shock and shifting alignment on the encoder. You know, catching air over defenses and all.

To echo one of the previous suggestions, I would highly recommend using a helical beam coupling to protect the encoder from shock and so you don’t have to stress out too much about alignment. Especially for this game. Since we seized up the one encoder, we’ve moved to using a helical beam coupling and have had no issues.

Surgical tubing and zip ties do this better and far cheaper than a beam coupling. It’s one of the best solutions we’ve shamelessly copied from other teams.

Here’s a picture of our solution. It’s a 3D printed 1/2" hex to 1/4" D-Shaft (the one on the encoder) coupler. We also have the 3D printed mounting brackets. Probably overkill, but we haven’t had any issues with the encoder seizing up throughout 12 matches this season, and countless practice hours.

I can send you the CAD if you want.

(PS. It’s the bright orange)