Update My thrust stand was poorly configured and the force data that I recorded was mostly garbage. I’m leaving my questions for posterity
The thrust stand was an L bracket resting on a scale, driven by a cube and custom motor test mavlink commands.
For this test, we used Vertiq ESCs 80-08 G2’s configured in “Voltage” throttle mode, which means that we pick a maximum voltage, and then the pwm value sent is interpreted as a percent of maximum voltage to send to the motor regardless of the voltage on the input bus (assuming that enough current can be supplied)
When using the above sheet and keeping this in mind, I figured it was appropriate not to change the voltage scaling column of the sheet, since I didn’t think that the input bus voltage drop would correlate to a loss of thrust (that is what I am assuming the calculation is for). If I’m incorrect, please advise.
The MOT_* settings on this sheet are educated guesses as to what we think will be appropriate for this craft. I can’t help but notice that after ~1200 PWM, the thrust curve appears quite linear. I’m not above thinking that this could be a measurement error of some kind.
This is the first time I’ve looked at this data to make these decisions, so I have some specific questions
1. Does this data pass the sniff test? NOPE
2. Does this data look suspiciously linear to you (especially after about 1250 PWM)? Garbage In Garbage Out
3. Given our expected takeoff weight at this time, a large part of the lower thrust curve will not be used in flight. Does this mean that it is appropriate for mot_pwm_min to be raised much higher (or alternatively, mot_spin_min to be raised higher) to something closer to of the scaled throttle as indicated on the sheet? Is it reasonable given this curve to raise mot_spin_min (or mot_pwm_min) and choose a lower expo value? This bird will spend most of it’s time hovering around the higher end of the thrust curve. Should we linearize the part of the curve where we expect to operate the most?
@amilcarlucas Before I hit send on this post I thought to check your guide and noticed you had made an updated spreadsheet. It seems that your corrected thrust plots account for the minimum pwm that will be seen in flight (aka the red line starts at the appropriate place, and tracks better than the original sheet), so I tried cutting off some of the lower range of the thrust curve and trying a lower EXPO value. I used my best guess as to what you intended with your “updated” G8 cell, where you wish to consider that the maximum thrust is the average of some range. With the original data, this seemed to cover from 10% throttle up to the maximum, but I’m not sure if this was really what you meant here.
I downloaded the ODS and reuploaded to Google sheets, which shows the graph nicely.
using methodic configurator worksheet instead
Edit: I am reviewing this guidance