Problem with Jags stopping unexpectedly

[wilsonmw04]

Greetings,

I am hoping the CD community can help my team with a pesky problem that popped up at the VA regional.

symptom: A drive motor will stop moving. Jag light will switch from green to solid red. The motor will stay unresponsive until roughly half a second after the drive command has stopped. Then resume normal operation. When put on blocks, all drive motors function normally.

What we have done to try and resolve the issue:

1. Replaced Jag. no change
2. replaced PWM wire. no change
3. Swapped PWM wire to another working drive motor on the robot. Problem went to that new motor.
4. changed PWM port via code. no change.
4. replaced DSC. no change.
5. replaced ribbon cable between DSC and CRIO. no change.
6. uploaded code that was working perfectly Friday morning. no change.
7. replaced joystick. no change.

The we have three things we can check now.
a.Replaced the motor on the drive, but that seems unnecessary because of results of #3 on the list above.

b. Replaced CRIO. This is a shot in the dark. Everything thing else on the robot is working as intended.

c. Bad snap action fuse. This is what I am hoping for.


Does anyone have any insights to this problem? We have one last event this week and would really like to resolve this issue quickly.

Help is Chief Delphi. You are our only hope.

[Jay O'Donnell]

Originally Posted by wilsonmw04

Greetings,

I am hoping the CD community can help my team with a pesky problem that popped up at the VA regional.

symptom: A drive motor will stop moving. Jag light will switch from green to solid red. The motor will stay unresponsive until roughly half a second after the drive command has stopped. Then resume normal operation. When put on blocks, all drive motors function normally.

What we have done to try and resolve the issue:

1. Replaced Jag. no change
2. replaced PWM wire. no change
3. Swapped PWM wire to another working drive motor on the robot. Problem went to that motor new motor.
4. changed PWM port via code. no change.
4. replaced DSC. no change.
5. replaced ribbon cable between DSC and CRIO. no change.
6. uploaded code that was working perfectly Friday morning. no change.
7. replaced joystick. no change.

The we have three things we can check now.
a.Replaced the motor on the drive, but that seems unnecessary because of results of #3 on the list above.

b. Replaced CRIO. This is a shot in the dark. Everything thing else on the robot is working as intended.

c. Bad snap action fuse. This is what I am hoping for.


Does anyone have any insights to this problem? We have one last event this week and would really like to resolve this issue quickly.

Help is Chief Delphi. You are our only hope.

I can't really offer any advice, but team 1058 had a similar problem throughout the 2012 season. We never really fixed the issue, and we did all of the same things you did. We've since stopped using jags (victors and talons have both worked perfectly for us).

[kevin.li.rit]

How are you controlling the Jaguar? Have you tried to measure the current to see if the jaguar is hitting the over temp or over current conditions and shutting down?

[Daniel_LaFleur]

Originally Posted by wilsonmw04

Greetings,

I am hoping the CD community can help my team with a pesky problem that popped up at the VA regional.

symptom: A drive motor will stop moving. Jag light will switch from green to solid red. The motor will stay unresponsive until roughly half a second after the drive command has stopped. Then resume normal operation. When put on blocks, all drive motors function normally.

What we have done to try and resolve the issue:

1. Replaced Jag. no change
2. replaced PWM wire. no change
3. Swapped PWM wire to another working drive motor on the robot. Problem went to that new motor.
4. changed PWM port via code. no change.
4. replaced DSC. no change.
5. replaced ribbon cable between DSC and CRIO. no change.
6. uploaded code that was working perfectly Friday morning. no change.
7. replaced joystick. no change.

The we have three things we can check now.
a.Replaced the motor on the drive, but that seems unnecessary because of results of #3 on the list above.

b. Replaced CRIO. This is a shot in the dark. Everything thing else on the robot is working as intended.

c. Bad snap action fuse. This is what I am hoping for.


Does anyone have any insights to this problem? We have one last event this week and would really like to resolve this issue quickly.

Help is Chief Delphi. You are our only hope.

When you changed to a different motor, was that motor on a different gearbox?

It sounds like you are tripping the overcurrent in the Jaguar. To test upload the default drive code (not a previous version of your code as it may also have the bug) and run it.

It's very possible that somewhere in your code you are giving 1 motor (of a multi motor drive) a different speed command.

[Al Skierkiewicz]

If the breaker opens, there will be no lights on the Jag, but it resets almost immediately. If the Jag faults for under volts, over current or over temp, it will fault by turning on the LED RED for 3.5 seconds if the fault has been removed.

[wilsonmw04]

Originally Posted by Daniel_LaFleur

When you changed to a different motor, was that motor on a different gearbox?

Yes. We are running an Octocanum with one cim per wheel pair.

[Ether]

This doesn't fit all the symptoms you described, but since it's so easy to do:

Try installing the voltage ramp jumper on the Jag that is giving you the trouble.

[wilsonmw04]

Originally Posted by Ether

This doesn't fit all the symptoms you described, but since it's so easy to do:

Try installing the voltage ramp jumper on the Jag that is giving you the trouble.

voltage ramp jumper? I didn't know it had such a feature, I will look into it now.

Edit: wow, that might just do it. I will swap those first thing Thursday. It's worth a shot.

[MrRoboSteve]

1. Is it possible that the Jaguars are calibrated differently?

2. Rather than running it on a test stand, I would instead simulate pushing during a match by pushing the robot against the wall or some other immovable object (not a mentor) for 4-5 second periods, with a couple second break between pushes. Do it on a carpeted surface so that you have similar resistance to a field. Can you get the issue to happen by doing this over a 2-3 minute period?

3. Per Daniel_LaFleur's suggestion, I'd look closely at your programming to see if you can figure out whether there's a state where you're having drivetrain elements oppose each other. If you don't already have it, consider adding some debugging logic at the point where you are setting the motors. One obvious condition to log would be when the two motors on the same side of the robot are commanded to drive in opposite directions when your grippy wheels are down. Depending on the precise nature of the change you made in #3 this may or may not be the problem.

[Michael Hill]

Originally Posted by Jay O'Donnell

I can't really offer any advice, but team 1058 had a similar problem throughout the 2012 season. We never really fixed the issue, and we did all of the same things you did. We've since stopped using jags (victors and talons have both worked perfectly for us).

We also had the same issues in 2012. We've vowed to never use Jags again and we've never been more happy!

[Joe Ross]

I agree that this sounds like it is hitting the current limit on the Jaguars, and that the automatic voltage ramp will likely work. VexPro Jaguars (and TI jaguars that have been upgraded with the v107 firmware) have a higher current limit. Is it possible that the working jaguars have the new firmware and the non-working one has older firmware? See http://www.vexrobotics.com/vexpro/mo.../217-3367.html

[Electronica1]

Originally Posted by Joe Ross

I agree that this sounds like it is hitting the current limit on the Jaguars, and that the automatic voltage ramp will likely work. VexPro Jaguars (and TI jaguars that have been upgraded with the v107 firmware) have a higher current limit. Is it possible that the working jaguars have the new firmware and the non-working one has older firmware? See http://www.vexrobotics.com/vexpro/mo.../217-3367.html

We are running 4 VexPro jags, and we tried to switch to a brand new jag fresh out of the box and the problem persisted.

[Nuttle89]

Originally Posted by Electronica1

We are running 4 VexPro jags, and we tried to switch to a brand new jag fresh out of the box and the problem persisted.

IIRC, even brand new Black Jags ship with the old firmware. I think we had a student flash all of ours with v107 when they first arrived. While updating the firmware might treat your symptom and allow the Jag to function normally, it sounds like you may have some mechanical fault in that module.

I'd recommend swapping the motor leads (post-Jag) and see if the problem stays with the physical motor to diagnose this.


OP, with #3, are you saying you took a PWM line going into the Jag, put it in a different Jag connected to a different mechanism, and that new Jag had the same problem? In that case my best guess would be that you're doing something odd in code like rapidly reversing the motor - this could cause Jags to current fault or otherwise misbehave.

If you do go to the trouble of updating the firmware, the good news is that you can read diagnostic info from the Jag via the BDC-Comm utility. You can manually drive the motor at varying voltage and watch for temperature or current spikes. If you have the cables lying around or can make them, having access to this can be helpful for diagnosing stubborn Jags.

[Danny Diaz]

Originally Posted by Nuttle89

IIRC, even brand new Black Jags ship with the old firmware.

Old firmware, new firmware, Jags shouldn't be used for drivetrains (in my humble but accurate opinion). A CIM will pull a little over 60Amps at "ideal torque", which is 150% above the rated Amperage of the 40A Snap-Action breaker. At that level, the breaker will draw that current for over a half-minute without issue. But the Black Jags with the OLD firmware will cut power at 60A after 2 seconds. With the NEW firmware, Black Jags will cut power at 93A. Okay, great, but old firmware versus new firmware doesn't really matter; the Black Jag will STILL cut power if the current draw exceeds 50A "for a short period". This is the "Progressive" software current cutoff in the firmware that isn't really documented anywhere except briefly on the website. Understand that the Black Jag was originally designed for use in applications where you don't necessarily have an external breaker protecting it!

We used Black Jags at Arkansas, and the robot's drivetrain felt very sluggish when starting from a dead stop or when turning (we kept slamming into the current cutoffs). For LSR we're dumping the Black Jags on our drivetrain in favor of Talons (who can handle 60A continuous and over 100A peak without the "progressive" cutoff), but we still are using Black Jags for other areas of our robot where we're taking advantage of the built-in limit switch connections on the Jags themselves; we can protect the robot much faster by killing the Jag directly than waiting for the software to get the message and do it for us.

-Danny

[geipel]

Danny,

I had heard this sentiment expressed before (about Jags on drivetrains), but this is the first time I had heard it with such a good explanation. This makes sense.

Thank you!