Follower wheel

Trying to design a small follower module with an encoder. Was thinking about a 2" wheel on a round shaft mounted to a AMT132Q-V encoder, supported by bearings on both sides of the wheel. Idea is that it would be placed under the center of a tank-drive robot and have a small compression spring to help keep it in contact with the ground.

But, I’m having problem finding 2" wheels that will either (a) press-fit onto a small round shaft (the encoder takes shaft sizes up to 5/8") or (b) will take a small hub for that shaft size. All the wheels I’ve found are designed to be on dead shafts.

Any suggestions? (I know that the follower wheel placement can be a problem if the field surface is not level. But, right now, this is just intended to try out technology on a pre-season robot.)

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Have you looked at FTC wheels and hubs? There are several FTC systems that use 5mm, 6mm and 0.250" axles, either round or D-shaped.

Check the Actobotics system at servocity.com. Here is a 2" wheel that might work. And there are wheel hubs here with different sizes for shafts between 0.125" and 12mm.

It sounds like you may be wanting to use the encoder shaft as the wheel shaft. It is doubtful that the encoder will withstand the forces and the shock.

It would probably be more robust to have the encoder connect to the wheel through a chain, gear or belt.

Yeah. That’s exactly what I’m trying to do.

It’s interesting that you’d say that. Is it just that specific encoder or encoders in general? Or is it just the design? Asking because that seems to be a fairly common thing in FRC. For example, the Vex Single Speed, Double Reduction gearbox has the encoder directly driven by the same shaft that the wheel sits on. Further, in the CD threads on the new motors (with integrated encoders), there are a number of comments about how the motor is the wrong place for the encoder and that it should really be on the thing you’re measuring – the output shaft.

If you are referring to the 217-2454 with the plastic casing, the output shaft is supported by two ball bearing races that absorb all of the physical loads and shocks put into the shaft by the wheel. The encoder shaft is turned by the output shaft. None of the physical loads and shocks should be transmitted into the encoder.

I originally thought you were intending to use the shaft of the encoder as the shaft of the wheel in which case the encoder would not hold up to the stresses from the wheel.

You can probably use any shaft that works for your wheel and turn it down to fit your encoder.

Alternatively, you can ask if the output shaft from the 217-2454 is available separately and see if it fits a suitable wheel. That shaft is already turned down to fit an encoder though you may have to cut it shorter for your application. AndyMark sells many different shafts from their various gearboxes and one of them might do the job for you.

So, I looked at the data sheet for the AMT132Q-V. It shows the housing bolting to a housing of some sort that supports the shaft (motor housing or gearbox). I was assuming that you were going to support the shaft by bearings in some sort of wheel fork or other type of housing and that the encoder would be mounted to that same housing. As long as the shaft is supported by that housing and not by the encoder itself, you should be fine.

Looking at the data sheet for the AMT132Q-V, it shows that there is a shaft adapter for 3/8" diameter shaft. You can also get a hub for the Actobotics wheels that would work with a 3/8" shaft and there are bearings available for 3/8" round shaft and you can buy 3/8" shaft at various outlets like Andymark or even at Home Depot or even use the shank of a 3/8" bolt as your axle. You should be able to do the same with 1/2" round shaft (there are hubs, adapters, and bearings available). If you were to use 1/2" shaft, you could use an aluminum tube instead of a steel shaft to save some weight.

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