SRX Encoder Breakout Options

We are going to be a second year team, and would like to incorporate more control in our robot this year. We have 4 talon SRX that we plan to use on the drivetrain (Kitbot). There are multiple different encoders and breakout boards that are available on AM. What would you recommend? Anything you’d avoid? Words of advice?

Currently we are thinking the SRX encoder breakout board (am-2633) right on the talon, and a E4T OEM Miniature Optical Encoder Kit (am-3132) on the gearboxes.

West Michigan Robotic Alliance just released a new breakout board you might want to consider. The idea for the the Sentinel Talon-SRX Breakout Board was conceived after FIRST Robotics Teams 141 and 2767 had experiences with breakout boards that had compatibility or ease of use issues when used with the Talon SRX.

The Sentinel Breakout Board is used to easily connect a wide variety of digital and analog signal inputs to the Talon SRX speed controller. Inputs supported include incremental and absolute encoders, travel limit switches, string pots, distance ranging sensors, and much more. The Sentinel Breakout Board combines the most features and status reporting of any Talon interface product on the market. The Sentinel was a collaborative effort, designed and manufactured by the West Michigan Robotic Alliance.

All technology developed by the West Michigan Robotic Alliance is open-source to the FIRST community.

Sentinel Product Page at AndyMark

I would suggest using the CTRE Mag encoder over the US digital one. It’s designed to works smoothly with the talon SRX and no breakout or custom wiring is necessary to use it.

The US digital encoders also use these tiny connector with tiny wires that always break on me at the worst possible moment no matter how hard I try to protect them. I’ve sworn that I’ll never use them again in anything mobile.


I’ve never used the US Digital encoders but we just ordered and installed some SRX Mag Encoders on a new drivetrain, and so far we like them. They weren’t too hard to install, but the downside is that it has to be somewhat placed precisely. There is a range you have to install them within, which is tight but these encoders should be very accurate and easy to use once it’s tuned properly.

I see in the manual that the CTRE encoder needs some lathe work on the toughbox shaft. Any suggestions for a work around or an option for those of us that don’t have a working lathe?

The biggest downside I have seen with these is the close distance that they need to be to the SRX/ The cables to connect the mag encoders to the SRX are hard to find in lengths >12". For those that like to have their electronics centrally located, this makes it difficult.

+1 to those that have a solution to this…

The E4T is the encoder that the Toughbox Mini housing/output shaft is designed to use. I haven’t had the issues with the connector that others have mentioned.

Has anyone had success using a file to face the shaft and a drill press instead of a lathe?

Another option might be to use printed parts to hold everything in place and mount the magnet in a live axle.


If you just want basic quadrature function, you can put encoder breakouts on each end of a normal 4 conductor cable with SRX cables connected from the breakouts to the devices. We used this method this year for our arm-mounted shooter.

so each side of the drivetrain has 2/3 motors each with a Talon SRX. but only 1 gearbox. Can the encoder on the gearbox be wired to multiple SRXs?

Technically, yes. You would get power and ground from one breakout and then the signal wires would go to both.

The more conventional way to do this is to have all of the processing on one SRX (per side) and have the other set to slave mode (i.e. they will give the same outputs). This is the better method, because it removes any chance of noise in the encoder wires causing a difference in the feedback loops, which would make the motors fight each other and lose efficiency.