Sprayer pump PWM-out won't change with increasing flight speed

Hello everyone, I am testing a spraying system controlled by the FC.
I have set up the following parameters:
I don’t use spinner
I have configured SERVO5 to function 22(sprayer pump)
PWM range 1500-1900, Trim 1500 (pump uses a brushed ESC which reverses below PMW 1500), and an RC-channel to turn on and off the pump.
The problem comes when I turn on the pump the SERVO5 PWM goes from 1500 to 1540, and doesn’t change any further, even when I drive around with the copter on the front seat of my car, with speeds of around 10m/s
Firmware version: ArduCopter V4.3.3
Any ideas on what’s preventing it from changing the PWM would be greatly appreciated.

Man, you have to perform some flight tests… really doesn’t expect this test to be representative, probably you have to be with your drone armed for the sprayer algorithm engage…

Also confused about this… you set the minimum PWM of your pump to 1500? This can lead potentialy lead you to some strange behaviour… go back to the default 1100 and calibrate your Pump ESC properly. The SPRAY_PUMP_MIN parameter will take care of the minimum ammount of PWM to apply when you fly at the SPRAY_SPEED_MIN speed.

Thank you for the reply, we were unable to do proper flight tests, due to bad weather.
On the next day I repeated the same test but removed the propellers and armed the drone in the car, and sure enough the PWM output for the pump started changing with speed. I am waiting for calm weather, and will continue with proper flight tests to confirm the correct dosing of the chemical.
I too prefer to use the whole range of the PWM output, but I had trouble calibrating the cheap ESC to work in only one direction in the whole PWM range. I will probably change to higher quality brushed ESCs

Probably it is, you can double check downloading the log and checking the PWM for the pump channel.


I thought you were using a brushless pump with a proper ESC. Keep in mind thar brushed controllers may need different PWM signal and can become a pain to control or lead you to unpredictable results. I would go for a brushless pump instead.