Avoiding Slippage and Proper Mounting of Andymark Absolute Encoder

This year we used two AndyMark Absolute Encoders AM-2389 on our robot. Overall they worked exceptionally well, with one large exception. They are fully rounded. They don’t have a key or a flat, and they slipped frequently as a result. We tried 3D printed mounts, gaskets, adhesives, and even press fitting up until it we felt it was going to break, and it still slipped.

Do you use these encoders? Are we doing this wrong? How do you mount these? Thanks

You could Mill/ cut your own flat/slot if you really felt it needed it. You could also use a different absolute encoder. Or it could be something bad with the encoders causing them to seem to slip but not actually slipping

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I haven’t used them on an FRC robot, but actually am using them right now on a university project. It’s a 6DOF robotic arm. They’re not directly tied to the output of the motor, rather somewhere along the belt drive with a pulley specifically for the encoder. We haven’t done extensive testing yet, but our approach was to decouple the encoder from experiencing the torque due to the mechanical system. If we encounter slippage we were planning to use various types of adhesives, eventually escalating to permanently bonding it to the pulley if need be. That’s a pretty expensive solution though and I really don’t think it’s the optimal one.

What kinds of adhesives did you try? Have you contacted Andymark to see what they think? Are you absolutely (hah, sorry) sure that it’s slippage and not something else?

PS. Congrats on innovation in control yesterday!

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We turn a shaft with a 1/4” boss, and then use a spring shaft coupler to couple the boss with the encoder. The encoder has a slim nut and a spring washer, which you can use to lock it down on a fixed plate.

Here’s a picture of what the stackup typically looks like:


We standardize on the distance between the two standoffs on the outside at 1.75", so all of our gearboxes have room for an encoder in the future.

You can use pretty much any coupler - these Amazon ones are what I believe we use: https://www.amazon.com/6-35x6-35mm-Flexible-Coupling-Motor-Coupler/dp/B00N732LVI

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Honestly, just a shaft coupler works. I’ve even seen people use zip tied surgical tubing. Though, I’ve press fit them on a 3d printed part with no issues. Is there a normal amount of resistance when turning?

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