Question about PWM and motor control with Raspberry Pi 4B and Lego Build HAT

[PinkPantherPC]

Hello everyone,

I am planning a project using a Raspberry Pi 4B and the Lego Build HAT to control motors and sensors. However, I have read that without using the pwm function, communication with the motors can be slow.

I got the information from another issue:

• Motors not starting at same time

Could someone clarify to what extent this slowness affects motor performance? Specifically:

• Do the motors start with a noticeable delay?
• Do the motors start at significantly different times?
• Are there any issues with sensor communication, or does that work without any problems?

Any insights or experiences you could share would be greatly appreciated.

Thank you for your help!

Best regards,
PinkPantherPC

[mutesplash]

What's "noticeable" and "significant"?

[PinkPantherPC]

By "noticeable," I mean whether there is a perceptible delay between when the command is issued in the program and when the motor actually starts running.

By "significant," I am referring to whether, when using MotorPair to start two motors simultaneously, the robot moves straight or veers off course due to differences in the starting times of the two motors.

This project involves a race with other robots, so it is crucial that the motors are extremely precise.

Thank you for your clarification!

[gregorianrants]

I have written an alternative library that overcomes this limitation of the official library.

you can find it here
https://github.com/gregorianrants/buildhat-alternative

[PinkPantherPC]

Thank you very much. It will be very useful as the official library seems to have some inaccuracies.

[hollielucas]

I might have come across this a bit late - but if it helps....
Two things need to born in mind:
1.) We cannot expect any two inexpensive "toy" motors to be assembled accurately enough to achieve the same start-up and running speed.
2.) The electronics cannot be expected to execute at exactly the same time. Quick as electric signals are, when running two devices "at the same time" the signal will always reach one device before the other.
Without doubt, some motors are better than others, some motor drivers are better than others, and some code is more efficient - but the components used to construct the Pi, the Build-hat, and the motor's rotary encoder may be no better than 20% accurate. Now, at the speed of electron flow those inaccuracies at may be very, very little in absolute terms, but they do add up. (An inexpensive "medical quality" brushless motor will cost into £ three figures, will Lego buyers pay this)?
I also understand, from another source, that the Linux OS does not lend itself to accurate timings due to it's strict garbage collection routines.