Ignoring the KV command, I continued down the calc it myself path. currently not sure my formula is correct.
my procedure ended up being like this. Use vesc-tool to run the motor at a fixed amps ( 3 amps in my case. ) let the motor spin up to 95% duty cycle. (doing lower duty cycles gives wildly varying results. )
then I sampled the realtime data 10 times by doing a screen grab of that section of the screen.
and in put it into a spreadsheet
left motor:
| power | Duty Cycle | erpm | battery current | motor current | volts-in | pole pairs | v=W/A | rpm | kv m1 | kv m2 | kv m3 | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 83.8 | 94.60% | 19109 | 2.08 | 2.57 | 40.8 | 7 | 32.61 | 2,730 | 88.5 | 83.7 | 70.7 | ||||||||||||
| 73.3 | 94.90% | 19159 | 1.82 | 2.26 | 40.8 | 7 | 32.43 | 2,737 | 88.9 | 84.4 | 70.7 | ||||||||||||
| 67.9 | 94.90% | 19203 | 1.68 | 2.07 | 40.8 | 7 | 32.80 | 2,743 | 88.1 | 83.6 | 70.9 | ||||||||||||
| 63.6 | 94.90% | 19231 | 1.57 | 1.94 | 40.8 | 7 | 32.78 | 2,747 | 88.3 | 83.8 | 71.0 | ||||||||||||
| 60.9 | 94.90% | 19255 | 1.51 | 1.87 | 40.8 | 7 | 32.57 | 2,751 | 89.0 | 84.5 | 71.0 | ||||||||||||
| 59.1 | 94.90% | 19299 | 1.46 | 1.8 | 40.8 | 7 | 32.83 | 2,757 | 88.5 | 84.0 | 71.2 | ||||||||||||
| 58 | 94.90% | 19311 | 1.44 | 1.77 | 40.8 | 7 | 32.77 | 2,759 | 88.7 | 84.2 | 71.2 | ||||||||||||
| 55.8 | 94.90% | 19345 | 1.38 | 1.7 | 40.8 | 7 | 32.82 | 2,764 | 88.7 | 84.2 | 71.4 | ||||||||||||
| 52.98 | 94.90% | 19361 | 1.31 | 1.61 | 40.8 | 7 | 32.91 | 2,766 | 88.6 | 84.1 | 71.4 | ||||||||||||
| 54.8 | 95.00% | 19375 | 1.36 | 1.69 | 40.8 | 7 | 32.43 | 2,768 | 89.9 | 85.4 | 71.4 |
right motor:
| power | Duty Cycle | erpm | battery current | motor current | volts-in | pole pairs | v=W/A | rpm | kv m1 | kv m2 | kv m3 | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 60.3 | 94.90% | 19230 | 1.49 | 1.83 | 40.8 | 7 | 32.95 | 2,747 | 87.9 | 83.4 | 71.0 | ||||||||||||
| 52.4 | 94.90% | 19261 | 1.29 | 1.64 | 40.8 | 7 | 31.95 | 2,752 | 90.7 | 86.1 | 71.1 | ||||||||||||
| 48.6 | 95.00% | 19280 | 1.2 | 1.47 | 40.8 | 7 | 33.06 | 2,754 | 87.7 | 83.3 | 71.1 | ||||||||||||
| 47.8 | 94.70% | 19309 | 1.16 | 1.4 | 40.8 | 7 | 34.14 | 2,758 | 85.3 | 80.8 | 71.4 | ||||||||||||
| 44 | 95.00% | 19330 | 1.08 | 1.34 | 40.8 | 7 | 32.84 | 2,761 | 88.5 | 84.1 | 71.2 | ||||||||||||
| 41 | 94.90% | 19352 | 1.01 | 1.26 | 40.8 | 7 | 32.54 | 2,765 | 89.5 | 85.0 | 71.4 | ||||||||||||
| 35.8 | 95.00% | 19367 | 0.88 | 1.11 | 40.8 | 7 | 32.25 | 2,767 | 90.3 | 85.8 | 71.4 | ||||||||||||
| 41.3 | 94.90% | 19381 | 1.02 | 1.25 | 40.8 | 7 | 33.04 | 2,769 | 88.3 | 83.8 | 71.5 | ||||||||||||
| 38.2 | 94.90% | 19393 | 0.94 | 1.16 | 40.8 | 7 | 32.93 | 2,770 | 88.6 | 84.1 | 71.6 | ||||||||||||
| 39 | 94.90% | 19401 | 0.96 | 1.18 | 40.8 | 7 | 33.05 | 2,772 | 88.4 | 83.9 | 71.6 | ||||||||||||
| 38 | 94.90% | 19419 | 0.94 | 1.16 | 40.8 | 7 | 32.76 | 2,774 | 89.2 | 84.7 | 71.6 |
I’ve listed two methods of kv calc. m1 is the process I followed above.
M2 is just RPM/Volts
I think M2 makes more sense because If Power is actually power in the motor then the duty cycle would already be accounted for. so don’t need to factor it again
Also m2 suggests these are probably nominally 85kv motors. ( I don’t think @hummieee did higher thatn that? ) m1 would suggest 89kv
edit: added m3 method. just take the input RPM/Effective Volts