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!

Re: Talon SRX and Analog Encoders
 

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?

Re: Talon SRX and Analog Encoders
 

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 :)

Re: Talon SRX and Analog Encoders
 

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

Re: Talon SRX and Analog Encoders
 

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.

Re: Talon SRX and Analog Encoders
 

Please explain in a bit more detail what you mean.

Re: Talon SRX and Analog Encoders
 

pretty sure he means how many times the roboRio runs the teleoperated loop very second...

I guess it depends how much code you run... you can find the number of iteration by printing the time each time you enter the loop... I don't know how that is useful for your PID control tough :confused:

Re: Talon SRX and Analog Encoders
 

Let me try again:

@Tbots: ..Please explain in a bit more detail the relationship between the TeleOp frequency and the bolded portion above.

Re: Talon SRX and Analog Encoders
 

In order to scale -1 to 1, the normal scale of the joystick, to 0 to 1024, we would have to add one and multiply by 512 the original value of the joystick. The problem is, since we would be using a joystick, whoever was driving would have to hold that position on the joystick else the wheel would return back to the the 512th position.

The only way I can think to avoid this, is if a button would increase the value of the angle while another one lowered it. The only problem is I'd have to know how often the tele-op vi was executed. Otherwise I wouldn't know by how much to increase the value. In other words, I wouldn't know how sensitive to make the joystick.

In the case that the button was held down, the wheel may have too large of an increase in angle and mess up the wires of the wheel. This is why I'd need to know how long it takes tele-op to execute, in order to determine what magnitude the decrease/increase would need to be.

Re: Talon SRX and Analog Encoders
 

MaGiC_PiKaChU, when connecting the encoders with the data cable and using a breadboard and resistors, how did you connect the data cable? It has two rows of holes in it, each with 5 holes. 2x5. How did you connect these to the breadboard?

Also, do you have to have a d-link connected to the robot in order to enter web-based configuration? We've never used web-based configuration, but we need to use it to configure the SRX.

Re: Talon SRX and Analog Encoders
 

In LabVIEW, the Teleop VI runs every time the robot receives a packet from the driver station, so the delay could be pretty irregular.

A way to achieve what I think you're looking for would be to measure the time delta between each run of Teleop, and multiply that by the joystick value before applying the scaling factor and integrating, to ensure that the joystick power is being applied "evenly" with respect to time.

For example:

Re: Talon SRX and Analog Encoders
 

1- we had tons of data cables, so we cut one side to connect each wire individually... you could also plug a small wire into each hole, but that would be harder

2- No, your RoboRio has its own IP address, it changes if you connect via USB or ethernet. I don't remember the defaults, because we changed it to 10.33.60.2 as soon as we got it. You can find this address somewhere in the user's manual :D

Re: Talon SRX and Analog Encoders
 

Cutting them would make it hard to plug them into the breakout board later. :( Just the same, we have had a lot of difficulty trying to find wires small enough to fit into the data cable's slots. Do you know what each hole does on the data cable?

The IP changes?? you mean it's not “roborio-XXXX.local”
where XXXX is the team number? It has an extension such as .2 or .6?

Re: Talon SRX and Analog Encoders
 

I've never heard of measuring time, but it sounds like a great idea! Ill see if I can find it.

Thank you for the help! :)

Re: Talon SRX and Analog Encoders
 

see my thumbnail

I don't remember... as long as you find the right IP you'll be able to configure your SRX... I always connected using 10.33.60.2, in my case