A (Different!) Acceleration Problem

[prionhost]

Hi, I've been encountering an issue regarding acceleration in a recent project. I've checked other issues (open/closed) and none have this specific acceleration problem and I've racked my brain enough that I'm looking for some help. Relevant info:

Arduino Nano hardware, 16MHz. Stepper pulses are at maximum 600, so being sub-kHz I figure the clock speed should not be relevant here. ContinuousStepper makes use of TimerOne for the ticker.

Attached here is a video of the issue, with acceleration at a value of 100.0 to emphasise the problem:
https://github.com/user-attachments/assets/259490be-2ff3-4047-a9c1-4e64fc289d79

During the period of acceleration, the motor is set to a speed above that of the target speed, only to decelerate to the target speed after 'acceleration' is finished. This results in a halting, jerking starts and stops.

Now, I'm not sure if this is the library's issue or mine, but I'm at my wit's end here - would be happy to show you the codebase if you're at all interested.

Thank you!

[bblanchon]

Hi @prionhost,

In the README, I see that I wrote "this example only proved to work correctly on Teensy 3.1".
Indeed, I think I tried other boards in my possession, and it only worked on Teensy 3.1.
I didn't write any additional explanation, but I suppose the TimerOne cannot be reliably restarted and triggers an additional time.

I may be able to workaround this issue by checking the timestamp in the interrupt handler.
Alternatively, I could set a fixed frequency based on the target speed.
In any case, I'm currently overwhelmed, so I don't know when I'll be able to test these options.

Can you try without TimerOne?

Best regards,
Benoit

[prionhost]

Hi @bblanchon, I appreciate you getting back to this. I did indeed see that in the README but assumed that other boards just weren't tested, not that they didn't work - per your advice I tried the KhoiH ticker rather than TimerOne, but AVR_PWM is not capable of a low enough step frequency (bottoms out at around 240 steps/s), while AVR_Slow_PWM has a maximum frequency of 500 Hz, which isn't quite high enough for my use case.

I may try to use ToneTicker instead, the 31 Hz minimum should be okay but I am unsure whether it will work yet. Will report back after some testing.

Thank you!

[bblanchon]

Please also test without any timer at all!

[prionhost]

Back after testing - unfortunately a non-interrupt loop will not work either, the LCD update code blocks for long enough that there is a stutter every 250ms during the rotation of the motor. Notably though the acceleration did work just fine! TimerOne seemed to have the best capability here, so I may try to see if I can get that working in the interim. If you have any other advice it would be greatly appreciated.

Thank you again!

[bblanchon]

I'm not surprised: screen updates do take a lot of CPU time.
In fact, that's the reason I added interrupt-based timers in this library.
However, I developed it with a Teensy 3.1, where the TimerOne library works really well (after all, the library was initially written by Paul Stoffregen)

I suggest you set up a fixed-frequency timer with TimerOne, and call stepper.loop() from the interrupt handler. The timer frequency should be at least 2x the step frequency (for high and low levels), but you can increase to 4x, 6x, or 8x to get a smoother acceleration.

Here is a draft code (not tested):

#include <ContinuousStepper.h>
#include <TimerOne.h>

ContinuousStepper<StepperDriver> stepper;

void setup() {
  stepper.begin(stepPin, dirPin);
  
  Timer1.initialize(1200); // or 2400, 3600, 4800...
  Timer1.attachInterrupt(+[](){ stepper.loop(); });

  stepper.spin(600);
}

void loop() {
  
}

If this works well, I could implement it in the library at some point.