Here are raw data for thrust and efficiency for tiny brushed and brushless motors and propellers. Later I’m going to analyze the data with more details.
1. Models for brushless and brushed are very different : from practical point of view brushless tiny whoop motor is more “responsive” at the throttle’s maximum.
2. There is no significance difference between 17k and 19k motors, both brushed and brushless.
3. 4blade (TBS and BetaFpv) propellers and 3 blade (BetaFpv) show similar performance.
4. ESC efficiency of brushed FC is close to 100%
5. ESC efficiency of brushless FC is much lower at low throttle and reaches 100% at throttle maximum (estimation, unfortunately I could not find a way for correct measurements of current at the brushless motor yet, so I used current at the battery and theoretical curves, but I’m pretty sure about this conclusion).
1. Test stand. This time I’ve improved motor holder. To avoid mechanical resonances, the holder was attached with soft porous material.
0716 (17500) (BetaFpv, obsolete)
0716 (19000) (BetaFpv)
0617 (25000) (BetaFpv)
all motors were unused before tests.
Uruav Battery 250 mAh, freshly charged at each test.
Below are raw data together with theoretical curves for 4blade Betafpv prop (dashed black lines, for guidelines, all fits use the same parameters for propeller (Cp and eff) and specific for the motor values Kv, R, I0). For brushless motors the voltage model was used (upd: 02/2019, this is incorrect, later I realized that the same PWM model should be used, but plotted against rpm), for brushed the brushed pwm model. See
Fig. 1 Brushed: All data can be reasonably fitted with our pwm model, no assumptions were made and the same propeller’s parameters were used. Efficiency (g/W) was calculated using V and I at the battery, so this includes also FC current. As earlier we can see that ESC efficiency is closed to 100%. Dashed lines show theoretical curves for 4bl BetaFpv prop (no fit, parameters as earlier). Note significantly lower efficiency of 0617 25k motor, see below.
Fig. 2 Brushless: All data can be reasonably fitted with the voltage model, no assumptions were made. Efficiency (g/W) was calculated using V and I at the battery. We can see that theoretical curves for efficiency are significantly higher than experimental at low throttle (upd: 02/19: not quite correct, later I realized that the same PWM model should be used, but plotted against rpm, the efficiency does not have a bump, but still higher than obtained in the experiment). The difference can be explained by low efficiency of ESC, this is also confirmed with lower overall efficiency derived from hovering time. Dashed lines show theoretical curves for 4bl betafpv prop (no fit, parameters as earlier)
0617 (25000) has almost 2 times less efficiency than 0716 motors. I would not recommend this motor. Also it has absurdly high no-load current:
Fig.3 No load current. No-load current of 0617 25k brushed motor (red) is significantly higher than no-load current for other brushed motors (green, blue). Also, this current is throttle (rpm) dependent, looks like viscous damping via air or bearings. I cannot make any conclusions on no-load current for brushless motor (olive), since the values for current at the battery include ESC, which is in contrast to brushed motor has low efficiency.