Servo Library seems to set pulse width modulation outside of acceptable range for a servo

[Eric Vanderhoof]

Hi there microblocks team! When using an RC car electronic speed control with pulse width modulation control, the controls lock up above 50% power setting. I took a look at the definition for the servo speed block, and it looks like the pulse width initialization math needs the 10 changed to a 5. The usual expected range for a servo is something like 1000 to 2000 microsecond pulses. 100% power with the current math would make it 2500, which falls outside that range. I made the correction locally and it fixed the issue, but it keeps coming up when my students update their servo libraries.

Thank you,

Eric Vanderhoof

[John Maloney]

That's not a bug.

Unfortunately, servo's differ, and some require a wider range of pulse widths than the standard 1000 to 2000 microsecond range. The current range was found to cover a wide variety of servos.

But it's unfortunate that your RC car doesn't like the out-of-range wider pulses.

Not sure what to do to make the servo library work with all servos. Maybe an intermediate scale between 10 and 5. Could you see if 8 works with your car?

[John Maloney]

I realized that the "set servo to speed" was independent of the "set servo to angle" block, so I made this change. It is in the latest pilot release, 1.2.51.

[Eric Vanderhoof]

Great, thank you!

I suppose a servo block could also be an expandable with “PWM Min” and “PWM Max” as inputs with a function inside to map percentages/angles to their corresponding PWM values. I’m not sure how the speed of the map block compares to simpler adding and subtracting though.

Thanks again!

Eric Vanderhoof