Talon SRX Motor Controller Problem

[FRC Team CC]

We have a problem connecting the motor controller to the PWM ports on the roboRIO. We believe to have correctly connected the motor controller to the roboRIO and the Power Distribution Module. When we connect the motor controller to the CAN port, the motor controller works. However, when we use the PWM ports, the motor controller doesn't work and just blinks red.

We took two photos of the system which are posted below.

Thanks for any help!

[Bkeeneykid]

Originally Posted by FTC Team CC

We have a problem connecting the motor controller to the PWM ports on the roboRIO. We believe to have correctly connected the motor controller to the roboRIO and the Power Distribution Module. When we connect the motor controller to the CAN port, the motor controller works. However, when we use the PWM ports, the motor controller doesn't work and just blinks red.

We took two photos of the system which are posted below.

Thanks for any help!

To use PWM, you need to flash the SRX using a different firmware. See section 1.3.4.2. PWM – Updating firmware for PWM use in the SRX's User Manual.

[ozrien]

That section explains that PWM CAL Mode and Limit Switches require the upgrade. General PWM drive does not require the update, however it is required to be FRC legal if the firmware is <0.28.

Your photo looks like the green wire is connected to the middle pin, which is not correct. Green should go to ground. See Section 1.3.3 of the Talon SRX User's Guide.

[dirtbikerxz]

Why are you attempting to run the SRXs from PWM anyway?

[FRC Team CC]

Neither of our wires are connected to the middle pin - the green is connected to ground. By our understanding, the problem with the CAN wires is that they employ series circuiting rather than parallel. So if one of the motor controllers goes out, then the others stop working. This is the reason we are trying to use PWM ports, but correct us if we wrong about this.

Thanks,
Charging Champions

[bobbysq]

Originally Posted by FTC Team CC

Neither of our wires are connected to the middle pin - the green is connected to ground. By our understanding, the problem with the CAN wires is that they employ series circuiting rather than parallel. So if one of the motor controllers goes out, then the others stop working. This is the reason we are trying to use PWM ports, but correct us if we wrong about this.

Thanks,
Charging Champions

Supposedly, both pairs of Talon SRX wires are continuous with each other. You should also note that if you use PWM, you don't get any of the nice PID and active brake and coast switching features.

[Ari423]

Originally Posted by bobbysq

You should also note that if you use PWM, you don't get any of the nice PID and active brake and coast switching features.

+1

For most teams that use Talon SRX's, the main reason is the built-in PID and active breaking software, which is only available via CAN. Obviously you already have these Talon SRX's, but in the future if you know you will only be using PWM you can buy cheaper motor controllers that do effectively the same thing. You can get SPARK motor controllers from REV Robotics for $45 (half the price of a Talon SRX). If you really need the small package, you can get Victor SP's ($60 IIRC). Of course this isn't to say that the Talon SRX's won't work with PWM, just that in the future there are cheaper alternatives.

[bobbysq]

Originally Posted by Ari423

You can get SPARK motor controllers from REV Robotics for $45 (half the price of a Talon SRX). If you really need the small package, you can get Victor SP's ($60 IIRC). Of course this isn't to say that the Talon SRX's won't work with PWM, just that in the future there are cheaper alternatives.

+1 to that too

Also, you should put some form of connector on your wires. It's possible you were shorting +5v to ground with your current setup. If you don't have the proper connectors and crimper, you can solder the wires to a preexisting PWM cable. Using connectors will also give you something good to attach the cables with if you decide to use CAN at some point, since I doubt you'll want to cut, restrip, and solder the wires every season, especially since the wires are permanently stuck to the controller.

[FRC Team CC]

Thank you all for the replies. A couple of questions:

1. So if we used the CAN ports, which don't use parallel circuiting, would it be right to say that if one motor controller were to stop receiving power, then the rest of them would not receive any inputs through the CAN wires?

2. Should we use Anderson Powerpoles to link together CAN wires or a different mechanism? What is the cleanest way of linking CAN wires?

We are probably going to stick with the CAN ports.

Thanks for the help,
Charging Champions

[dirtbikerxz]

Originally Posted by FTC Team CC

Thank you all for the replies. A couple of questions:

1. So if we used the CAN ports, which don't use parallel circuiting, would it be right to say that if one motor controller were to stop receiving power, then the rest of them would not receive any inputs through the CAN wires?

2. Should we use Anderson Powerpoles to link together CAN wires or a different mechanism? What is the cleanest way of linking CAN wires?

We are probably going to stick with the CAN ports.

Thanks for the help,
Charging Champions

1. I believe the input and output CAN wires on a talon are soldered to the same place. So even if one motor controller were to lose power, the rest should still work. ( Someone correct me if I'm wrong). Also, it is really rare that only one of your motor controllers should lose power, especially if the wiring was done correctly.

2. We always cut our CAN wires to the exact length and solder them together and cover in heatshrink. Makes really clean runs. If we need more length on one wire later on, we can always just solder on more wire, or if it comes to it, take apart the motor controller housing and compltley swap out the wire (it's not too hard).

[Bkeeneykid]

Originally Posted by FTC Team CC

Thank you all for the replies. A couple of questions:

1. So if we used the CAN ports, which don't use parallel circuiting, would it be right to say that if one motor controller were to stop receiving power, then the rest of them would not receive any inputs through the CAN wires?

2. Should we use Anderson Powerpoles to link together CAN wires or a different mechanism? What is the cleanest way of linking CAN wires?

We are probably going to stick with the CAN ports.

Thanks for the help,
Charging Champions

We used CTR's CAN Connector Pack to connect our SRXs this year. They worked great, just put some electrical tape over the exposed solder points on the bottom (just in case). Makes it very simple to re wire the CAN network (as we had to do as we needed more motor controllers suddenly), and means you don't risk damaging the cables much with other connectors. It uses the same connectors as on the PDP, PCM and roboRIO. It may not be the cleanest way (our board was not very clean this year), but it certainly makes it easy to change later. Anderson connectors would be cleaner cut to the right length, but for the CAN wires, these connectors are overkill. Try .1" pitch PWM wires maybe instead?

And as Rohit said, most CAN devices just connect high-high and low-low and just take that signal elsewhere for processing. Also, you don't have much probability of one dying on you. Though more likely, if one died your code would crash as it couldn't initialize the CANTalon anymore. That's assuming the entire thing just died rather than the just the voltage controlling circuitry, which is more likely. The SRX is advanced enough to have current limiting and the such, and because of that I've never seen a dead one.

[RufflesRidge]

Originally Posted by Bkeeneykid

Also, you don't have much probability of one dying on you.

A breaker trip will cause a single controller to lose power.

As others have noted though, the controller losing power will not interrupt your CAN chain.

Though more likely, if one died your code would crash as it couldn't initialize the CANTalon anymore.

This should not crash WPILib code, it will just throw errors into the log.

[frcguy]

Originally Posted by Bkeeneykid

Well for one, that's not FRC Legal. *Standard warning about 2016 rules may not apply to 2017* See rule R70:



You can only either directly connect to the roboRIO or daisy chain through another device.

I'm not sure about the legality, but I know for sure some teams ran with a star topology during this past season. However, I've heard that it's not a great method for connecting everything. Check out this post for more info on why it isn't recommended: https://www.chiefdelphi.com/forums/s...2&postcount=12.

[dirtbikerxz]

Originally Posted by frcguy

I'm not sure about the legality, but I know for sure some teams ran with a star topology during this past season. However, I've heard that it's not a great method for connecting everything. Check out this post for more info on why it isn't recommended: https://www.chiefdelphi.com/forums/s...2&postcount=12.

If I understand R70 correctly, star topology is technically illegal. I guess many people (including me) didn't realize that.

[Dwight_2]

Originally Posted by FTC Team CC

We have a problem connecting the motor controller to the PWM ports on the roboRIO. We believe to have correctly connected the motor controller to the roboRIO and the Power Distribution Module. When we connect the motor controller to the CAN port, the motor controller works. However, when we use the PWM ports, the motor controller doesn't work and just blinks red.

We took two photos of the system which are posted below.

Thanks for any help!

My team had the exact opposite happen to our promotional robot (t-Shirt cannon), where the can connection blinked red and the PWM connection worked fine with a slight change in programing.