Talon SRX and Analog Encoders

[TBots]

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!

[Ether]

I've hear that the SRX have 'built-in' PID controllers. Is this true?

Yes.

And if so, do I still need to include PID in our labVIEW programming?

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.

[MaGiC_PiKaChU]

Originally Posted by Ether

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.

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

[TBots]

Originally Posted by MaGiC_PiKaChU

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

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?

[ozrien]

Originally Posted by TBots

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?

Here's a snippet from the link Ether mentioned....

This breakout board is designed specifically for use with the Talon SRX - it scales a native 5V analog signal to a Talon SRX compliant 3.3V, helping 5V magnetic shaft encoders to "just work" without additional circuitry.
...
See section 1.4.7 of the Talon SRX User's Guide for more details.

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).

[Ether]

Originally Posted by ozrien

Here's a snippet from the link Ether mentioned...

Gotta give Antoine credit for that link :-)

[TBots]

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?

[MaGiC_PiKaChU]

Originally Posted by TBots

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?

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

[TBots]

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.

[MaGiC_PiKaChU]

Originally Posted by TBots

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.

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

[TBots]

looks good Thank you for the help!

[TBots]

Ether, what did you mean when you said this?

Originally Posted by Ether

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

Do you mean the difference in the current position of the encoder and the set point?

[MaGiC_PiKaChU]

Originally Posted by TBots

Ether, what did you mean when you said this?

Do you mean the difference in the current position of the encoder and the set point?

You have a command probably called "SetPID"... It allows you to place your parameters for the PID control, when you control with the position. You call this once before your control loop. if you never worked with PIDs before, I'm pretty sure Ether could help you

[Ether]

Originally Posted by TBots

Do you mean the difference in the current position of the encoder and the set point?

No. Watch this video. It explains what PID gains are.

[TBots]

Ah I see, you just mean the constants associated with PID. I understand now.

How frequent is the tele-op code executed on the roboRIO?

I need to know so I can choose the sensitivity of the joystick. Ill then use the values of the joystick in the math for the set point.