RPM1 and RPM2 on same input

ArduCopter Copter 4.7
1

Is it possible to use the same input for RPM1 and RPM2?
The FC is an AET-H743-Basic; the RPM input is Servo12 (Pin 61).
My configuration would look like this:

SERVO12_FUNCTION=-1
RPM1_TYPE=2
RPM1_PIN=61
RPM1SCALING=0.0147058824

RPM2_TYPE=2
RPM2_PIN=61
RPM2SCALING=0.06617647058823529411764705882353

Would this work, or do I need separate pins for RPM1 and RPM2?

2

As a GPIO I’m going to expect you’d need two separate pins for RPM1 and RPM2.

3

Yes, it looks like it.

I tested it and it doesn’t work.

4

Why do you need two scalings of the same RPM?

You can drop the scaling factor by 2 and you will be able to set notches on harmonics of both signals. Unless both RPMs are mechanically coupled (eg. main and tail rotor) I would strongly recommend using separate RPM sensor to drive the notches as notch tracking failure can introduce significant noise into the control loop.

5

It’s a heli. RPM1 is the main rotor, RPM2 the tail rotor.
Both have the same rpm source (the motor) but different scalings.
Tail rotor rpm is 4.5 times main rotor rpm.

6
  1. If you have a clutch you should use a physical RPM sensor on rotor side of the one way bearing/clutch.
  2. I would check if you even need tail rotor RPM to drive any notches
  3. If you do, you can set notch frequency scaling to 1/2 and harmonics as needed (1st MR harmonic (fundamental frequency) will become second harmonic, 2nd MR harmonic will be 4th in the filter etc., TR fundamental frequency will become 9th harmonic).
7

Thanks for the tips; I’ll give it a try.