New Talon Speed Controller

[Ether]

Originally Posted by Jon Stratis

Of note, the data you gathered didn't seem to show this same result, which leads to a question of which data set more accurately reflects real-world usage on a FIRST robot.

The first graph you linked was using a Window motor, not a CIM, with unknown torque load.

The second graph you linked was using a CIM with unknown (and possibly changing) torque.

All the testing I did was with a CIM motor on a dynamometer with measured torque load.

So it's difficult to compare the data.

[Tom Line]

Originally Posted by Jared341

The AndyMark product page for the Talon (http://www.andymark.com/Talon-p/am-2195.htm) says something interesting:

"Do you want your motor to hold it's position after power is cut?"

How does the Talon provide this? Does it stay in brake mode even after power is removed?

That is correct, and we're verified it.

It stays in brake after pwm signal is removed.

[AdamHeard]

Originally Posted by Tom Line

That is correct, and we're verified it.

It stays in brake after power is removed.

Is there still a jumper to enable/disable brake mode?

[Tom Line]

Originally Posted by AdamHeard

Is there still a jumper to enable/disable brake mode?

Yes there is.

However, one thing we didn't verify is what happens if the jumper is set to coast and the pwm signal is killed.

Mike C. can probably answer that without us doing another test.

[Jon Stratis]

Originally Posted by Ether

So it's difficult to compare the data.

Agreed!

Ultimately, graphs can only tell you so much... the real "proof" is what the drivers think when you stick some of these onto a drive train. I know when we switched from Victors 884's to Jaguars, there was a noticeable improvement in our ability to control the robot. Would there be a noticeable difference switching between Victor 888's, Jaguar's, and Talon's? Personally, I wish I had about $400 to spare so we could buy 4 Talons and 4 Victor 888's and swap them out on last year's robot!

[Ether]

Originally Posted by Ether

So it's difficult to compare the data.

When you're trying to do closed-loop control of speed, you might want to see what the torque response vs command looks like at various speeds.

So I just wrote an awk script to re-arrange the raw RPM vs Nm data to provide a family of curves of Nm vs IPW¹ at various RPM levels.

Here's the result:
http://ether.comeze.com/FRC/WMCT801/


¹ input pulse width in ms

[flameout]

Originally Posted by Tom Line

It stays in brake after power is removed.

The way I'm interpreting this is that, after the main breaker is switched off, dynamic braking still occurs (i.e. the output is still shorted). This is very different from saying that the behavior at a neutral command is to dynamically brake the motor.

Could you confirm that brake mode persists after the main breaker is switched off? This could become a serious issue when teams need to push the robot around by hand.

Also, if this really is the case (I'm skeptical), could someone answer how this (feature apparently?) was implemented.

[s1900ahon]

Originally Posted by flameout

The way I'm interpreting this is that, after the main breaker is switched off, dynamic braking still occurs.

I would not have interpreted it they way you have. I would have interpreted it as that when the PWM signal is disabled (flatlined) the Talon continues to apply brake mode if the brake/coast jumper is set to brake.

When the main breaker is switched off, power is cut to everything, including all Talons, Victors, and Jaguars. At that point, the MOSFETs in the H-Bridge turn off and the only conduction possible is through the reverse body diodes.

[flameout]

Originally Posted by s1900ahon

I would not have interpreted it they way you have. I would have interpreted it as that when the PWM signal is disabled (flatlined) the Talon continues to apply brake mode if the brake/coast jumper is set to brake.

That makes sense, and matches the behavior of every other FRC-legal motor controller.

When the main breaker is switched off, power is cut to everything, including all Talons, Victors, and Jaguars. At that point, the MOSFETs in the H-Bridge turn off and the only conduction possible is through the reverse body diodes.

This is why I'm skeptical -- and why I was curious to know how my interpretation is possible.

I'll assume your interpretation is correct, then, unless someone comes in and confirms that mine was correct.

Thanks for clearing that up.

[Mike Copioli]

Originally Posted by Jared341

The AndyMark product page for the Talon (http://www.andymark.com/Talon-p/am-2195.htm) says something interesting:

"Do you want your motor to hold it's position after power is cut?"

How does the Talon provide this? Does it stay in brake mode even after power is removed?

This is a misprint. It should read "when disabled" not "after power is cut".

[Mike Copioli]

Originally Posted by s1900ahon

I would not have interpreted it they way you have. I would have interpreted it as that when the PWM signal is disabled (flatlined) the Talon continues to apply brake mode if the brake/coast jumper is set to brake.

When the main breaker is switched off, power is cut to everything, including all Talons, Victors, and Jaguars. At that point, the MOSFETs in the H-Bridge turn off and the only conduction possible is through the reverse body diodes.

Scott, you are correct.

[Tom Bottiglieri]

Has anyone with a Talon trying to control it with a cRIO/WPILib found a set of PWM signal timings that work well? The source for the Victor notes that signal acceptance between units was a bit off and I was wondering if this can be attributed to the signal generator or consumer side. I have a feeling this can be chalked up to poor calibration on the Victor as the cRIO generating sloppy signals seems less likely.

If no one responds we will run a test across 4 Talons to find timings that work, then post the results here and to WPILib.

From Victor.cpp:

/*
* Note that the Victor uses the following bounds for PWM values.  These values were determined
 * empirically through experimentation during the 2008 beta testing of the new control system.
 * Testing during the beta period revealed a significant amount of variation between Victors.
 * The values below are chosen to ensure that teams using the default values should be able to
 * get "full power" with the maximum and minimum values.  For better performance, teams may wish
 * to measure these values on their own Victors and set the bounds to the particular values
 * measured for the actual Victors they were be using. 
 *   - 210 = full "forward"
 *   - 138 = the "high end" of the deadband range
 *   - 132 = center of the deadband range (off)
 *   - 126 = the "low end" of the deadband range
 *   - 56 = full "reverse"
 */

[Ether]

Using a custom PWM signal generator, I have run the Vic888 with periods from 5ms to 20ms, and with pulse widths from .5ms to 2.5ms with no problems. I believe I did the same with the Talon, also with no problems.

[edit] I have not tested whether the motor controllers would calibrate properly to this pulse width range [/edit]

[Joe Ross]

Originally Posted by Ether

Using a custom PWM signal generator, I have run the Vic888 with periods from 5ms to 20ms, and with pulse widths from .5ms to 2.5ms with no problems. I believe I did the same with the Talon, also with no problems.

[edit]
Just calibrated an 888 driving a 500 ohm resistive load. Calibrated to 2.000 ms max, 1.000 ms min, and 1.500 ms neutral. Then measured, and got 1.990 ms max, 1.021 ms min, and deadband from 1.482 ms to 1.523 ms
[/edit]

The problem that the comment that Tom is referring to was finding what values work best with factory default calibration, and with the Victor 884, it varied unit to unit.

[Ether]

FWIW. Vic888 calibration using 500 ohm resistive load.