Blown Jrk 21v3 /advice possible groundloop

Support Motor controllers/drivers and motors
1

Dear people.

I am equipping a throttle quadrant of a boeing 737 with DC servomotors using 5 Pololu 21V3 dcmotor controllers.

Everything worked fine wich means that all motors are succesfully driven. until I transferred the software to another PC. At a certain moment I saw that when controlling one DC-motor, the other servomotors also moved very slightly. Strange because that wasn’t the case on the first PC. Soon I noticed that two DC-motors stopped working.

First of all, I checked the DC-motors and one motor turned out to be defective. Then checked the jrk 12v3 controllers, there was one defective.

Summary:
Two control elements no longer worked,
• One control element was defective and had a defective Servomotor
• An other control element was defective and had a defective Jrk 21V3

I have now ordered a new servo.

The defective Jrk 21v3 does not cause any problems in the controller software, you can clearly see that the motor receives voltage, but phisically the motor does not receive voltage at the terminals on the PCB. Even after reinstalling the firmware (v 1.3) there is no voltage coming at the motor terminals on the PCB.

For the power supply I use a 12 volt 60A server power supply.

I have connected all the USB controllers to a USB Hub with its own power supply.

I have the impression that somewhere a ground loop is created and that somewhere high currents are flowing in the circuits. However, I have no idea where……and how to prevent that.

How do I make my setup immune to groundloop?

I think I should investigate this problem further before installing a new motorcontroller and put the powerssupply on again.

Resume:
• How do I make my setup immune to groundloop? Is there detailed documentation available?
• It may be that the motor control on the Jrk 21.v3 PCB has become defective. Even though the behaviors in the controller software and the LEDs on the PCB are good.
• In Europe the motor controllers are difficult to obtain, does anyone have an address to buy them there?

Kind regards Leo

2

In addition to above:
If I only connect 12Volt supply voltage to possibly faulty Jrk21V3 then the yellow led flashes slowly. (aprox 1 flash a second) (USB not connected)

Kind regards,
Leo

3

Hello, Leo.

Why do you think the issues are caused by a ground loop? A more common issue we see (especially with people building simulators) is Jrks being damaged from trying to use them with motors that are more powerful than the motor controller was designed to handle. What motor were you trying to use the Jrk with when it stopped working?

If you want to troubleshoot the problematic Jrk 21v3, then to start I would recommend removing it from your larger system and testing it in a simple a setup as you can. If you just try to control the Jrk over a direct USB connection to your computer using the Jrk Configuration Utility with nothing else connected to it except for a power supply and a multimeter monitoring the outputs, do you see any voltage applied on the output pins? Are any errors reported by the configuration utility, and can you post some pictures of that setup that show all of your connections?

We have several European distributors. Here is a link to our distributors page.

We do not monitor what each of our distributors currently have in stock, but you can use the “View distributor profile…” link under each distributors name to check what products they have ordered from us recently. Alternatively, you can order our products directly from us, you can find more information on our “Ordering” page.

- Patrick

4

Hi Patrick,

Thank you very much for your answer.

The whole throttle worked like charm, until I switched to another PC

QUOTE: Why do you think the issues are caused by a ground loop?

I did read somthing about is in the forum. I have checked thee resistance between all groundpoints and the powersupplies and resistance was below the 1ohm. I checked also the tension between the different earthpoints and that was ) Volt, so I think there is no earth problem.

QUOTE: What motor were you trying to use the Jrk with when it stopped working?

I am using the Modelcraft RB350030-0A101R DC Motor

Specs
Demensions (Ø x l) 37 mm x 72 mm
Diameter 37 mm
Length 72 mm
Max. aandrijvingsbelasting 6 kg/cm · permanent 2 kg/cm
Gear eduction 1:30
Nominal Voltage 12 V
Max. Current 2.1 A
Axel length 12 mm
Axel-Ø 6 mm
Supply Voltage 12 V/DC
Max. torque 60 Ncm
Free rpm nom. Voltage 200 omw/min
Loaded RPM 174 omw/min

QUOTE: If you just try to control the Jrk over a direct USB connection to your computer using the Jrk Configuration

That is exactly what I did. I can control the Jrk 21V3 in the Configuration Utility but there is no error in the error tab but there is also no Voltage on the motor terminals. It seems that the motordriver on the PCB is lost

Pictures:
Two of the five JRk’s the lowest one is defective and I have it removed.

Here you can see four of the Jrk’s

This is the defective Jrk
If I connect 12Volt supply only to the faulty Jrk21V3 then the yellow led flashes slowly. (aprox 1 flash a second) (USB not connected), No errors in cofig app and no voltage on motorterminals.

QUOTE: Here is a [link to our distributors page](https://www.pololu.com/distributors)

Thank you, I did find this page and I have checked the distributers, most of them have the G2 version availlable based on Pololu’s advice. This version is not supported in the Prosim flightsimulator software.

Kind regards,
Leo

5

Thank you for the additional information and pictures. It is unusual that your Jrk is not indicating a motor driver error, but at this point it does appear likely that it has somehow been damaged.

The motor you indicated seems reasonable for the Jrk 21v3, and there are not visible signs of components being damaged on the board, so unfortunately there is not an obvious explanation for what happened. If you post pictures of the bottom side of the board, I can look at the soldering and let you know if I notice any problems there.

You might consider looking at your system with an oscilloscope to check for problematic behavior, like voltage spikes on the supply voltage. One possibility is if one or more motors in your system stopped suddenly, they would have tried to dump current back to the power supply, but if your supply has some protection against that then that could have caused a damaging voltage spike on the Jrk’s VIN pin instead. If you find your system is generating voltage spikes, adding some protection like TVS diodes or maybe some of our shunt regulators might help.

However, it is also possible that you might have just gotten unlucky with something like an electrostatic discharge (ESD) shock.

- Patrick