Intermittent jerks of BLDC motor at ~45 Volts and above

Problem :
I notice that the motor jerks intermittently when it is operated above 40-45 volts. This becomes more frequent when the supply voltage in increased.

Setup:
1) RoboteQ SBL1360 controller
2) BLDC motor rated at 48V (200W)
3) Regulated DC power supply
4) Set the controller to run a simple script (operating in closed loop speed control, with gains P=0, I=2, D=0)

Observations:
1) When operating in the 24-36V region the jerks are not observed.
2) When operating above 45V the jerks are observed (intermittent, on average once every 5mins with no particular pattern). They become more frequent as the voltage is increased (tested upto 52V)
3) Changing the power supply unit does not improve the situation
4) Change of controller does not solve the problem
4) The jerky motion occurs because the motor comes to an abrupt halt
5) Problem observed in open loop mode as well

Can you please help me fix this problem. Let me know if any further information is required.

Do you have the serial watchdog set at the default 1000 ms? (in Configuration tab/command safety/) If so, you may have a momentary shutdown once a second (but erratically) with a Wait (1000) in your script.

The serial watchdog is set to the default value of 1000. Should this be increased ?

I tried changing the wait period in the script to 500ms and I still observe the problem.

By setting the wait time to 500 ms you've already done the right test for this - the problem is not caused by a watchdog timeout. I hope that the Roboteq people will have an answer for you.
Ciao,
Lenny

I'm also seeing this issue with our SBL1360 running at 50V nominal pack voltage - except we're getting jerks every few seconds, sometimes more than 1 per second.
It's pretty violent when the motor is running at speed, we're worried we are going to damage something.

This is with a Nanotec DB80M048030 motor, 8-pole bldc 600W (www.nanotec.de), The controller is set up in closed-loop speed/position mode with an external magnetic encoder IC sensing a magnet on the motor shaft (Infineon TLE5012B magnetic quadrature encoder IC set to 1024 pulses/rev)
We've set the controller to use both Hall and encoder feedback

The jerks also occur at lower voltages and speeds, but are less severe. When they occur, Roborun+ utility shows both the Hall rpm and encoder rpm values jumping from "normal" motor speed to -5 for just one update period, then back to "normal"

I also saw the same jerk behavior in open-loop mode, but only at high voltages (> 30-odd V), not at 24V

Is there a fix for this?

thanks

Richard Bebbington
GX Design Engineers
www.gxgroup.com