Talon SRX and Analog Encoders
 

We just got some Talon SRX motor controllers and are working on understanding all of their potential. Mainly, we need to figure out how to hook up and use a magnetic absolute encoder (MA3) to each of our SRX. The SRX will be what controls the turning of our wheels in a swerve drive.

I've hear that the SRX have 'built-in' PID controllers. Is this true? And if so, do I still need to include PID in our labVIEW programming?

There are several examples of using the talon SRX in the software manual that was included with the SRX, but we are unable to distinguish which of them we are meant to use.

Thank you for the help! :)

Re: Talon SRX and Analog Encoders
 

Yes.


No. But you do need to do the following:

- connect the feedback sensor directly to the Talon (not the roboRIO)

- use CAN bus (not PWM) to control the Talon

- use the appropriate CAN commands to tell Talon what closed-loop mode you want (e.g. position or speed etc)

- use the appropriate CAN commands to set the gains in the Talon's PID controller.

- use the appropriate CAN commands to communicate the desired setpoint to the Talon's PID so it knows what value you want it to control to.

Re: Talon SRX and Analog Encoders
 

also you'll need one of those for each talon
http://www.vexrobotics.com/217-4401.html

We had 14 SRX this year, 12 of them with a sensor in the breakout... This is amazing

Re: Talon SRX and Analog Encoders
 

Is it absolutely necessary to use the breakout board? It may be messy, but could you accomplish the same thing without it? What exactly does it do? Is it just making it easier to use the SRX?

Re: Talon SRX and Analog Encoders
 

Here's a snippet from the link Ether mentioned....
So in other words the MA3 is a 0-5V sensor, but the Talon analog input takes 0-3.3V (also in electrical specs in user's guide).

Re: Talon SRX and Analog Encoders
 

Gotta give Antoine credit for that link :-)

Re: Talon SRX and Analog Encoders
 

Alright I understand what is it now, but is it the only way to turn 5V of analog signal to 3.3? I'm asking because while the breakout board would be helpful, it doesn't look like we will be getting it any time soon seeing how it is currently sold out.

I still think it might be possible to recreate it, but maybe I don't yet understand the uniqueness of it. The talon SRX user guide makes the comment that the board is useful in the aspect that is uses "a resistor divider and voltage buffer" to make the 5V to 3.3V transition. What are these, and where are they located on the board? Is is something to do with the A63A?

Re: Talon SRX and Analog Encoders
 

we made a custom 5 to 3.3V converter on a breadboard at first...
pretty simple, but would highly recommend the breakouts with the designed cable

Re: Talon SRX and Analog Encoders
 

What is the "Q1" in the diagram?

Did it still work with the breadboard design? I mean, was there a major flaw in it, or did the breakout board just work better?

Yes the breakout board would be preferable, but if there is no way to get it at this moment, we would like to try alternate methods.

Re: Talon SRX and Analog Encoders
 

breadboard works, just takes a lot of space... As this is an offseason project, you should be fine.
breakout also allows you to use multiple sensors easily on a single SRX.

this diagram is an easier circuit you could use. The other was working both ways

http://www.savagecircuits.com/attach...6&d=1430452949

Re: Talon SRX and Analog Encoders
 

looks good :) Thank you for the help!

Re: Talon SRX and Analog Encoders
 

No problem :) Good luck with your project!

Re: Talon SRX and Analog Encoders
 

The Talon SRX Software Manual mentions that "the Set Output VI is also the method for specifying the setpoint." How can this be? I thought all the set output VI did was change the motion of the motor specified to either clock-wise or counter clock-wise and at your chosen speed. how can it also change setpoint?

If you wanted to change the position of the motor to the 90 degree mark, what value would you enter? Normally the VI's values range from -1 to 1. So how can you place an angle? What would be the range of values?

Re: Talon SRX and Analog Encoders
 

i'm not sure about LabView, but with Java it's also the same command;

depending on the Control mode, the input will not have the same effect

for example, we used "PercentVBus" during teleop, which ranges from -1 to 1
we used it like this
During autonomous, we used "Position" , which ranges from 0 to 1024 (0V on the sensor to 3.3V)
we used it like this
I guess it's the same with Labview, but I might as well be wrong :yikes:

Re: Talon SRX and Analog Encoders
 

I see what you mean. There is a similar command in labVIEW when initializing the Talon SRX objects to change it from PercentVBus to Position, I just never knew what it meant! Thanks for clearing that up!