# Way to reduce motor arming spin speed in PX4 params?

Source: https://forum.modalai.com/topic/3046/way-to-reduce-motor-arming-spin-speed-in-px4-params
Category: General Questions (https://forum.modalai.com/category/2/general-questions)
Posted: 2024-01-24 13:30:54 UTC by Matthew Wellner
Replies: 1 · Views: 1110

## Matthew Wellner · 2024-01-24 13:30:54 UTC

Hi,

Is there a parameter in the PX4 params to set the speed at which the motors spin up when you arm? On my first test flight after calibrating my ModalAI 4in1 ESC, as soon as I armed the quad it started to take off. Maybe I should reduce the minimum motor RPM in the ESC's configuration?

Thanks!
Matt

## Reply by Alex Kushleyev (ModalAI staff) · 2024-01-24 19:42:37 UTC

@Matthew-Wellner,

The ESC params should have `min_rpm` parameter set to the minimum RPM that you obtained during your tests, specifically the RPM that motor spins when you send `./voxl-esc-spin.py --power 10` command, as 10% power is pretty much the minimum you would want to use on the ESC itself.

Then you make sure your PX4 params also use this value for `min_rpm` for the following param: `VOXL_ESC_RPM_MIN` , however you also want to make sure the `max_rpm` ESC param corresponds to `VOXL_ESC_RPM_MAX` in PX4 params, otherwise the rpm range will not work correctly in PX4.

You should also do some sanity checking. Knowing your propeller's `thrust vs rpm` curve helps a lot. Then you can check the commanded / actual motor RPMs  versus your vehicles weight. It is possible to build a very lightweight vehicle, such that even small amount of thrust % would result in above hover thrust. You typically want to avoid those situations because it would be hard to achieve stable flight.

Finally, you should check your px4 log, you could load it here to generate plots, including actuator commands and reported RPMS and you can check if those RPMs make sense. https://review.px4.io/ . Please take note that this is a public site.