Problem with servo SG90 (and grbl)

Other Hardware Motors, Mechanics, Power and CNC
1

The latest release of grbl, firmware for CNC machines, has by default one pin dedicated to PWM. As far as I understand, if I provide a relevant g-code (e.g. M3 S200) the PWM signal changes accordingly.

However, it seems SG90 does not work. I suppose that the PWM signal has to be configured specifically in grbl code, but what should I look for exactly?

2

I doubt grbl is intended to control hobby servos. I haven't used grbl but I'd imagine the PWM output is for sending step pulses to a stepper driver.

I don't see how it would work with a hobby servo.

3

While grbl naturally works with stepper motors for axis positions, recently it has also added PWM control for additional equipment, such as drills, lasers, etc. To quote the docs:

With v0.9 and variable spindle PWM enabled, the D11 pin will output a range of voltages from 0V to 5V depending the spindle speed G-code command. 0V indicates spindle off in this case.

But on reading the tech sheet for SG90 indeed the principle of operation seems to be different.

4

Jabberwock:
recently it has also added PWM control for additional equipment,

Thanks for the clarification.

A lot of people think it's too bad the servo's input signal is so frequently called PWM. It's very different than what a laser or drill would need.

There are several servo examples in the Arduino IDE. I'm sure you could get lots of help if you wanted to use a different method to control the servo.

5

I strongly suspect the PWM signal produced by GRBL is designed to control the power going to a DC motor and has nothing to do with the signal needed to get a servo to move to a specific angle.

For servos the pulse width defines the position (angle). For DC motors the pulse width determines the power. They are not interchangeable.

...R

6

maybe late to post here
but there is a GRBL version for a servo on pin 11:

working here with arduino uno 2 stepper motors and a HTX900 micro servo

7

This will still come in handy, although I will probably need to swap the firmware when I want to use a laser instead of the pen attachment.

8

DuaneDegn:
I doubt grbl is intended to control hobby servos. I haven't used grbl but I'd imagine the PWM output is for sending step pulses to a stepper driver.

No its for the spindle I think - there's G-code to set spindle speed.