Hello all. We are a relatively older team that is using Mecanum Wheels for the first time. To move autonomously, we would like to employ the usage of encoders. Our drive train is using 4 CIM motors for our mecanum wheels. In regards to motor controllers, we are using VictorSPs and Spark Motor controllers with PWM ports. What would be the best encoder to use? Thank you for your help.
If you’re using CIMs and not using motor controllers with CAN and Data Ports (like Talon SRX’s) and without more info on which gearboxes you guys are using, I’d probably recommend the CIMcoder which is a 2 channel quadrature encoder with 20 pulses per channel per revolution that easily wires into 2 digital inputs of your RoboRIO (so that’s 8 inputs for all four motors…). Things of note are that these mount directly to the shaft of your CIM motor, so you’ll need to convert the pulses to account for your gearbox ratios if you want to get Wheel rotation and not CIM motor rotations.
Additionally, if you want more resolution than 20pulses/channel per revolution, you can get the Hi-Resolution CIMCoder which gives you 256pulses/channel per revolution. The one downside is you’ll need to convert the TalonSRX Data Port style Pinout to duponts for your RoboRIO, which you may be able to do with the TalonSRX Encoder Breakout Board, but I’ve never actually tried it, so attempt at your own risk.
If you’re using one of the compatible gearboxes, you could also use these Mini Optical Encoders that mount to the output shaft of the compatible gearboxes, and also give a 2 channel quadrature output with 360 pulses/channel per revolution. Also, no conversion would be necessary since it would be mounted directly to the output shaft, giving you a handy measurement of the degrees your wheels have turned.
The place to start is with your gearboxes, as the best place to measure speed is on the output axle, as (mechanically) close to the wheel as possible. What gearboxes are you using? Is there an encoder which is easy to interface to that? If not, perhaps the Rev through bore encoder, which you can put on a hex shaft.
We, 6838, have been using mecanums for a long time and we have tried many solutions suggested here. Programmers before me have tried CIMcoder and the Mini Optical Encoder and they seemed to not get great results for them. However, I am almost %100 sure that it was because of not careful installation of encoders or lack of programmer skills. I, personally, have worked with Mag SRX encoders and they are just great as encoders. The only downside is their mounting is harder than it should be. I would recommend running them with Talon SRXs but they should be good enough standalone. Also, if you are not doing any holonomic movement in auto with your drivetrain, you might get away with 2 encoders (+2 talons if you use them) to do path.
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