Pololu JRK G2 24v13 overheating

Support Motor controllers/drivers and motors
1

Hi

I’m having drastic overheating issues with the G2 24v13 connected to a Glideforce MD122008-P Medium-Duty Linear actuator.

The actuator doesn’t actually have any load on it, and it’s barely ever moving.

What I believe is happening is that the PID isn’t very well calibrated (I used Pololu’s provided PID settings), and the actuator is essentially constantly trying to find its position. Eventually the board is getting red hot.

What I did to mitigate this is to turn down the duty cycle, and turn the acceleration down to 50, and set the motor to coast when not moving.

Additionally, as I am controlling the motors position with the Arduino G2 library, I am sending it jrk.stopMotor() when I finish my movement. I thought this had fixed it, but a client has informed me the motor controller is red hot and has switched itself off.

The movement itself is very simple and only happening every couple of minutes.

When I was monitoring the JRK when I sent the jrk.stopMotor command the current reading was 0ma, so I assumed this was all OK.

Can you give me some advice here?
Things to note:

  • the jrk is rated for that actuator
  • what specifically does jrk.stopmotor() do? Does this make any difference?
  • What sort of startup time does the JRK have? One option is I turn it on each time with my Arduino and a relay before it moves.

I’ve used these boards quite a lot and never had this issue – and I’ve done properly demanding things with them. I’m a bit puzzled as to what specifically is causing this this time?

Any help would be much appreciated!
Thanks

2

Hello.

I would not expect the Jrk G2 24v13 to have any problems handling that actuator, so I suspect something might be either damaged or shorting somewhere.

The stopMotor() command triggers the “Awaiting command” error flag. The specific behavior after that depends on your other settings, as described in the “Stop motor” entry of the “Command reference” section of the Jrk G2 user’s guide, but ultimately, it should stop the motor and either brake or coast.

Which components or area of the board is getting hot? Does the Jrk controller still get hot if you run it with the actuator’s motor leads disconnected? Could you post some pictures of the setup that show all of your connections? A video showing the typical behavior while it is running might be helpful too. Also, could you post a copy of your current Jrk G2 settings file? You can save a copy of your settings file from the “File” drop-down menu of the Jrk G2 Configuraiton Utility while the controller is connected.

Brandon

3

Hi,

It’s the actual main IC on the board that gets hot.

It’s totally fine when not connected to the motor. And actually it has previously run fine for several hours with the motor connected – maybe after about 9 hours it gets extremely - ie. burn yourself - hot. FYI the movements are very sporadic, like once a minute.

I worked out the issue, though. Despite having used your preconfigured settings file for the actuator, there is something wrong with how the PID has been setup. Basically on one end of its range it can’t work out where it is, and just constantly searches for it. This in the end results in huge current draws accross the board, ie. the motor is constantly accelerating and decellerating. Even with stop motor command from arduino it turns itself on again and tries to find its target. I can see overshoot / pid problems in the jrk board software. Everything is protected with an incredibly beefy shunt regulator so it’s purely power draw and not voltage spikes which has done for me here.

I got it working again briefly basically turning it on with a relay before each movement but it’s totally burned itself out now and has died. I can’t get it to come on at all, neither via 12V in or usb bus power.

I’ve always found you pid settings very “hot” on your preset files and would normally set it up myself, but didn’t this time, which I’m now regretting having to deal with a furious client. Do you think you’d maybe look into whether these settings files are definitely the best you can do?

Is there any more advice you can give in terms of diagnosing? I don’t now have access to the physical unit as it’s been put on a truck and taken back to the workshop.

My settings were your factory settings for that linear actuator, but I’d turned down duty cycle to 350, accel to 50, brake to coast. And I current limited it to 10A. Everything else was the same as your medium actuator settings file.

EDIT: Incase it helps for troubleshooting, I did find the initial Pololu settings file very aggressive. In combination with PID and acceleration values the motor under no load would draw huge amounts of amps when it moved - 20A, 30A or so, therefore way outside the boards limits. I trust that Pololu know a lot more about motors than I do, and I have older JRK boards that have been in nearly continuous use for 10 years or so, so I know it’s a good product.

I’m also guessing your config files are set for a general/averaged use case – ie. PID configuration is probably task and load dependant, and isn’t fully one size fits all.

Would it be normal that at uncapped accel/decell duty cycles there would be this sort of current draw issue with this actuator and the JRK? I’m keen to find a solution in case they want it fixed for a future time. My guess currently is I throw away the broken JRK and try another one – but that gets expensive fast if I keep destroying them. I know there’s always the possibility of the odd bad board, but I’m also guessing that Pololu’s QC is good, so am keen to explore other, possibly more likely, reasons.

4

Hello.

Unfortunately, it’s difficult to meaningfully troubleshoot if you no longer have access to the system.

The ideal PID settings are definitely system-dependent. Our settings files are intended to be a good starting point at light loads, but additional tuning might be required if these defaults are not working well for a particular system. It sounds like you have already done this custom tuning for your system, so I’m curious why you aren’t just using the settings you’ve already determined work well for you. By the way, if you are having trouble getting a particular unit tuned, you can post here and we might be able to assist you.

Please note that a DC motor will briefly draw around twice the stall current if you go directly from full power in one direction to full power in the other direction, and this is generally independent of PID settings. This could explain the ~20A spikes you mentioned. To avoid acceleration-based current spikes like this, you would want to enable acceleration limiting. Another way to keep your system cooler is to use a Jrk version that can deliver more current (e.g. the Jrk G2 18v19 or Jrk G2 18v27, which are fine for 12V systems), but at that point you might just be shifting the problem to the actuator.

- Patrick