# Propeller Coefficients for Starling V2

Source: https://forum.modalai.com/topic/2521/propeller-coefficients-for-starling-v2
Category: General Questions (https://forum.modalai.com/category/2/general-questions)
Tags: starlingv2, propellers
Posted: 2023-08-01 20:24:08 UTC by Kashish Garg 0
Replies: 1 · Views: 1638

## Kashish Garg 0 · 2023-08-01 20:24:08 UTC

We were curious if anyone (either as users or from the ModalAI team) has been able to ascertain the propeller coefficients (thrust vs rpm / rpm vs throttle) for the props that come with the Starling V2? We are looking for coefficients specifically to be used for SO3 Control

## Reply by Alex Kushleyev (ModalAI staff) · 2023-08-02 14:39:03 UTC

Hello @Kashish-Garg-0 

we have a curve that is "motor voltage vs rpm", meaning that for a desired RPM, it tells the ESC what average motor voltage should be applied. The average motor voltage is defined as `battery_voltage * motor_pmw_duty_cycle`. The battery voltage in this curve is in millivolts. Since you are typically controlling the desired RPM, as a user you do not need to worry about what "throttle" or voltage to apply - the ESC does this automatically in order to achieve the desired RPM. this calibration curve is used as a feed-forward term in the RPM controller. The ESC does support an "open loop" type of control where you specify the power from 0 to 100%, which is similar to a standard ESC, but PX4 does not use that ESC control mode.

By the way, you can test the ESC directly (not using PX4) using our `voxl-esc` tools (https://gitlab.com/voxl-public/voxl-sdk/utilities/voxl-esc/-/tree/master/voxl-esc-tools) which works directly on VOXL2 or a standalone linux PC (or mac). `voxl-esc-spin.py` has a `--power` argument where you specify the power from 0 to 100, which translates directly to the average duty cycle applied to the motor.

Here is the calibration for the Starling V2 motor / propeller that we use:
https://gitlab.com/voxl-public/voxl-sdk/utilities/voxl-esc/-/blob/master/voxl-esc-params/mavic_mini_2/mavic_mini_2.xml?ref_type=heads#L63

Also, you can take a look at this post to see how to interpret those parameters `a0, a1, a2` : https://forum.modalai.com/topic/2522/esc-calibration/2

We also have some dyno tests for this motor / propeller : https://gitlab.com/voxl-public/flight-core-px4/dyno_data/-/blob/master/data/mavic_mini2_timing_test/mavic_mini2_modal_esc_pusher_7.4V_timing0.csv . We are not sure how accurate that is, but it can be used as a starting point. @James-Strawson can you please confirm that is the correct dyno data for the Starling V2 motors?

Alex