Dynamic Brake/Coast Modes?

[seg9585]

I have a potential mechanism application for which it would be desirable to dynamically switch between brake and coast modes on a speed controller via software rather than setting a mode prior to a match via a switch or calibration button.

Do any of the legal speed controllers currently support such an application? I have not used CAN control on the Talons before, so I wasn't sure if the Talons could be programmed with this functionality. I know the Jaguar is configured via jumpers -- is it legal to create a custom circuit that will allow electronic switching of the jumper position?

[GeeTwo]

The Talon SRX can dynamically set brake/coast when operating in CAN mode.

See section 2.1.3 of the Talon SRX User's Guide.

This refers you to the various language references.

[Al Skierkiewicz]

Any speed controller that has a brake/coast jumper can have that jumper connected to a digital I/O and be controlled in software. We have done it many times in the past. CAN is also an alternative.

[GeeTwo]

Originally Posted by Al Skierkiewicz

Any speed controller that has a brake/coast jumper can have that jumper connected to a digital I/O and be controlled in software. We have done it many times in the past.

Wouldn't this violate both R66 and R68?

Originally Posted by R66

The Driver Station software, roboRIO, Power Distribution Panel, Pneumatics Control Modules, Voltage Regulator Modules, RSL, 120A breaker, motor controllers, relay modules, Wireless Bridge, and batteries shall not be tampered with, modified, or adjusted in any way (tampering includes drilling, cutting, machining, rewiring, disassembling, etc.), with the following exceptions:

• A. User programmable code in the roboRIO may be customized.
• B. Motor controllers may be calibrated as described in owner’s manuals.
• C. Fans may be attached to motor controllers and may be powered from the power input terminals.
• D. If powering the compressor, the fuse on a Spike H-Bridge Relay may be replaced with a 20A Snap-Action circuit breaker.
• E. Wires, cables, and signal lines may be connected via the standard connection points provided on the devices.
• F. Fasteners (including adhesives) may be used to attach the device to the OPERATOR CONSOLE or ROBOT or to secure cables to the device.
• G. Thermal interface material may be used to improve heat conduction.
• H. Labeling may be applied to indicate device purpose, connectivity, functional performance, etc.
• I. Jumpers may be changed from their default location.
• J. Limit switch jumpers may be removed from a Jaguar motor controller and a custom limit switch circuit may be substituted.
• K. Device firmware may be updated with manufacturer supplied firmware.
• L. Integral wires on the Victor SP or Talon SRX may be cut, stripped, and/or connectorized.
• M. Devices may be repaired, provided the performance and specifications of the device after the repair are identical to those before the repair.
• N. The cover may be removed from the Talon SRX data port.

Bullet I says that you can move the jumper, not replace it with a cable.

Originally Posted by R68

Every relay module, servo, and PWM motor controller shall be connected to a corresponding port (relays to Relay ports, servos and PWM controllers to PWM ports) on the roboRIO (either directly or through a WCP Spartan Sensor Board) or via a legal MXP connection (per R69). They shall not be controlled by signals from any other source.

As I read this, the DIO is not a legal way to control a PWM motor controller.

[Jon Stratis]

Originally Posted by GeeTwo

Wouldn't this violate both R66 and R68?


Bullet I says that you can move the jumper, not replace it with a cable.



As I read this, the DIO is not a legal way to control a PWM motor controller.

For R66, I could classify Al's solution under part E - a pin is a pin, and the controller reads it as a signal. All the jumper does is set that signal to something steady.

For R88, I think the controller is still being controlled by the PWM port - the DIO hooked up to the coast/break header won't cause the motor to move at any time, only the PWM signal will do that. The DIO signal will just change the performance characteristics of the controller when it's being used by the PWM signal.

[Al Skierkiewicz]

What Jon said, this is for the brake/coast jumper only. I believe bullet J also applies.

[ozrien]

All good points...
Java example demonstrating section 2.1.3. java function here...
https://github.com/CrossTheRoadElec/...bot/Robot.java

[s1900ahon]

Originally Posted by Al Skierkiewicz

Any speed controller that has a brake/coast jumper can have that jumper connected to a digital I/O and be controlled in software. We have done it many times in the past.

This concept has always bothered me, a bit, for a couple of reasons:
1. On the Jaguar, the BRAKE sensor pin (middle one) is a direct input to the MCU which has 3.3V IOs (which are 5V tolerant, but still). In retrospect, we really should have put an ESD suppression device on that pin (he says looking at the last version of the schematics).

But more so,
2. When you've done this in the past, did you also connect ground? I.e. Was the DIO connection to the brake/coast jumper 2 wires (signal+ground), or just one wire (signal only)? I presume you did single wire. I ask since the PWM input of motor controllers use optoisolators so that the only ground return from the motor controller is V-. Connecting to the brake/coast jumper with 2 pins introduces a second ground return which may bear more current should the V- get disconnected, even momentarily.

I don't recall seeing any documentation for how to do the dynamic brake/coast. I don't recall providing this in the Jaguar docs. I don't recall seeing it in the Victor (but that was a while ago for me).

[Al Skierkiewicz]

Scott,
This is not using the PWM interface, ever. The Brake/Coast jumper is a pulled up input. Close the contact to common and it pulls down into the other state on those devices that use this feature. So you are supplying a closing contact to ground and no voltage in either state. This is my preferred method of interfacing to external control electronics. I don't like volts...

[GeeTwo]

Bullet J of R66 refers specifically to the limit switch jumpers, not the brake/coast jumper. Applying bullet E assumes that a jumper pin is a standard connection point, which isn't clear. The other arguments don't convince me either, though this is a case where I'd like to be wrong; it would have provided a simple solution to a design problem a few years ago, but I thought it illegal. I have asked about this on the Q&A.

Originally Posted by Q646

In this post: http://www.chiefdelphi.com/forums/sh...81&postcount=3 and following, it is suggested that the brake/coast pin of a PWM-controlled motor controller may be wired to a control signal from the RoboRIO's DIO port. I read this as a violation of R68, and as a modification beyond the wording of R66, especially bullet I. Others there see it as legal. Is this practice permitted? If allowed, I suggest providing clarification in the rules as to how to wire this safely.

Second Edit: I'll also post the answer here to close the loop for future generations.

[Al Skierkiewicz]

Guys,
There is no rule that prevents this use of the Brake/Coast jumpers. R66 lists allowed modifications to electrical components. The removal of a jumper and the connection to a DIO output is what was intended by the manufacturer starting with the Victor 883 and has been allowed since that device was introduced in FRC robots.
The bullet that refers to the limit switch input on Jaguars has a history to their first introduction and the firmware that was used at that time. To make it clear for present day users, Bullet J was added.
R68 has no bearing on the Brake/Coast jumper. R68 requires that all PWM controls originate in the RoboRio directly or through the listed MXP devices to insure that FMS will stop all motors used on an FRC robot when so commanded.

[cgmv123]

The GDC says it's a violation of R68. I suspect Al may convince them to change the rule when they review the ruling with inspectors. https://frc-qa.firstinspires.org//Qu...ired-to-a-cont

[Al Skierkiewicz]

Everyone,
In a discussion with Engineering, certain conditions could produce a hazardous condition. (verified during component testing) The current Q&A response is the only way to prevent this condition from occurring in all legal controller implementations on FRC robots. The Q&A response will be enforced at least for FRC season 2016. Sorry for the confusion.

[Thad House]

Originally Posted by Al Skierkiewicz

Everyone,
In a discussion with Engineering, certain conditions could produce a hazardous condition. (verified during component testing) The current Q&A response is the only way to prevent this condition from occurring in all legal controller implementations on FRC robots. The Q&A response will be enforced at least for FRC season 2016. Sorry for the confusion.

Is this an issue with the new controllers, or one of the old ones? I am also curious on what the issue actually is too. Does one of the controllers allow enable if the jumper isn't set correctly. And switching the jumpers manually between brake and coast is still allowed, right?

[Al Skierkiewicz]

Moving the jumpers are legal as specified in R66.i.
If a power return cable were to open under certain conditions, full current might flow in the jumper cable common lead.