speed is not updated correctly when stepper is already moving

[DreiDe]

I'm changing the speed of an ESP32 controlled moving stepper multiple times a second in intervals between ~100Us/Pulse - 40000Us/Pulse without a real acceleration phase in between. While at the beginning the stepper keeps following the set speed as expected, after some changes further updates are ignored and the old speed is kept.

From a feeling I would say it takes maximum 10 updates until it starts happening and higher rotation speeds are more likely to persist, however I couldn't find any real pattern. When the stepper movement is stopped and restarted speed updates again work at first but are ignored then.

This behavior occurs no matter if I'm using runForward(), runBackward(), moveTo(), move() setSpeedInUs(), setSpeedInMilliHz.

Did you ever experience this behavior @gin66? Or do you have any idea what the cause could be? And especially how it can be prevented/fixed?

#include "FastAccelStepper.h"

// As in StepperDemo for Motor 1 on ESP32
#define dirPinStepper 14
#define stepPinStepper 17

FastAccelStepperEngine engine = FastAccelStepperEngine();
FastAccelStepper *stepper;

void setup() {
    Serial.begin(115200);
    engine.init();

    // pins are set to outputs here automatically
    stepper = engine.stepperConnectToPin(stepPinStepper);
    stepper->setDirectionPin(dirPinStepper);
    stepper->setAcceleration(1000000);
}

void loop() {
    int targetSpeed = rand() % 40000 + 100;
    stepper->setSpeedInUs(targetSpeed);  // the parameter is us/step !!!
    stepper->runForward();
    delay(500);
    Serial.printf("target: %d\n", targetSpeed);
    Serial.printf("actual: %d\n", stepper->getCurrentSpeedInUs());
}

target: 6033
actual: 6033
target: 17843
actual: 17843
target: 16362
actual: 16362
target: 31629
actual: 31629
target: 29800
actual: 29800
target: 35608
actual: 35608
target: 29852
actual: 29852
target: 7356
actual: 7356
target: 17356
actual: 17356
target: 38219
actual: 17356
target: 19811
actual: 17356
target: 28451
actual: 17356
target: 12943
actual: 12943
target: 38805
actual: 38805
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actual: 34208
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actual: 26493
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actual: 38430
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actual: 17466
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actual: 12269
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actual: 38032
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actual: 27017
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actual: 29947
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actual: 18072
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actual: 32968
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actual: 7080
target: 26323
actual: 26323
target: 38649
actual: 26323
target: 7692
actual: 7692
target: 8264
actual: 8264
target: 16269
actual: 8264
target: 6651
actual: 6651
target: 30527
actual: 30527
target: 36290
actual: 30527
target: 22724
actual: 22724
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actual: 735
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actual: 735
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actual: 735
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actual: 735
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actual: 735
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actual: 735
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actual: 497
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actual: 706
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actual: 706
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actual: 706
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actual: 706
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actual: 706
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actual: 706
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actual: 706
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actual: 142
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actual: 706
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actual: 706
target: 9974

[gin66]

Thanks for reporting and same issue here. I have added it as another example. Just with my hw configuration.

Still investigating about the root cause. v0.24.2 works v0.25.4 works v0.25.5 works v0.25.6 fails v0.25.7 fails

[gin66]

v0.28.2 will fix this issue.

For a given acceleration, the speed jumps from 0 to a value appropriate for the first step (call it v1). If now the requested new speed v is lower than this first step speed v1, then this speed setting was just ignored. The fix was to set the speed to the requested speed v, if the ramp generator cannot reduce the speed anymore.

[DreiDe]

Ok, great, that was an instant fix :D Thanks a lot for your quick support! I just tested it and can confirm that the speed update works again.