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Topic-icon Jitter on Skid Turn

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6 months 1 week ago #29533417 by taakinsi

Our robot platform is a 4WD AGV that drives in skid steer with the wheels on each side connected to a motor (so two motors total). In certain scenarios, there is a lot of jitter when it makes a turn and I'm looking to understand why. Using FBL2360.

Case 1: Max amps is set at 25A per motor in the controller. On turning, motor amps goes to 25A and battery is about 2.5A per motor (so I believe this means it is running at 10% PWM). PID is (0, 0.5, 0). In this case, the motor jitters as it makes the turn. The motors do not stall which leads me to believe they are not at their max torque. Integral gain of 0.3 has been tried and no improvement. Integral gains of 1 and 2 have been tried and it gets worse.

Case 2: The same load as case 1 but this time, max amps in the controller is set to 40A. PID (0, 0.5, 0). In this case, the robot turns with no problems.

My first thought was the jitters in case 1 were caused by gains but adjusting gains has not helped. Why would increasing the amps in case 2 cause the turn to be smoother when we are not at max power in case 1? The low PWM in case 1 leads me to believe the controller is not using the max power allowed under the 25A limit.

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6 months 1 week ago #29533420 by Gabriel_Isko

It looks like your motor's bus current is more than 25A during it's turn, and the controller is hitting its current limit. This can be due to flyback current from the motor caused by regeneration. You can confirm this by logging your Motor amps using a Microbasic script.

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