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Constant RPM not accurate - Please help

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TooSlow2Care
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Joined: 2020-02-19 17:40
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Constant RPM not accurate - Please help

Hello,

I'm trying to get my motor to run at a specific RPM.  I have set up the VESC 4.20HW with 5.0/5.1SW to operate from a PPM/PWM App Config.

I have the VESC tool set properly and can get the motor to start and stop at the push of a button.

the Hardware I'm using:

Arduino Nano - PWM control, Acceleration ramp, timer (60sec)

VESC ESC 4.20

Outrunner sensorless 280kv BLDC Motor

6 cell and 8 cell lithium battery packs capable of up to 60A draw continuous along with a laboratory power supply.

My target is 4000rpm, from my 14pole motor. this means that (4000*[14/2]) = 28000 ERPM. Even while reading the data stream on VESC Tool live, I'm only seeing 26000 ERPM regardless of input voltage or amperage available. the ESC is not being taxed at all nor is the battery or laboratory power supply. I have checked and verified that my motor has 14poles and is measured to run 280kv

I started adjusting the PID controller kP value up, but this has not made any change (positive or negative) to the operation of the motor.

If I overshoot the ERPM setting to 32000 which should be 4751rpm at the motor, I'm only reading 4000rpm from my optical tachometer.

If I have missed a setting in the VESC Tool setup anywhere, please help. I'd also like to utilized the PID controller while it reads the BEMF data to maintain a constant RPM at the motor.

 

Thank you for any help you can provide,

TS

TooSlow2Care
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Last seen: 3 weeks 6 days ago
Joined: 2020-02-19 17:40
Posts: 5

After further research and testing, I have selected 'PID Speed Control No Reverse'  in the App Control under PPM, General.

I would think this would activate the PID control loop under the Motor Settings, PID Controllers... Please keep in mind that I am running a sensorless BLDC motor and relying on the BEMF and Sensorless measurement to input data to the PID controller.

As a next step am I to increase the PID values to enable the PID controller?

 

Thank you,

TS

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Luke264
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Joined: 2020-09-30 19:46
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The discrepancy could be from stator vs magnet pole count, check your erpm calculations carefully!

To get the pid speed controller to hold the speeds I need I have to start over with new current kp/ki disregarding detection values, then slowly tweak kp/ki on the pid screen. Also, reduce brake current to a tiny fraction of forward current, it plays havok with tuning.