Can you give me some specific examples of what you're looking at? I typically look at around 400-600g of thrust because that is the typical flying range for a motor.
Ok, knowing to look at that thrust range is good to know, thanks for the tip. In that case the difference is much less pronounced but still definitely there. What I'm most confused about is that (in any case) the trends in g/W as thrust decreases are completely different. Is the explanation in the differing levels of motor tech?
Thanks for the quick reply. I'm sorry this is belated, but I think I messed up on my original the day of, or it got lost in the system or something.
The 400-600g rule of thumb is good to know, thanks. At that point the difference is smaller but still definitely there.
I'm looking at the EMAX RS2205S and the Cobra CM2204, on the 4x4x3 for comparison. But the trends hold true for most of the props.
The EMAX stays roughly around 3g/w for most of the throttle band, except idle where is goes down around 1. The cobra starts at around the same at top end and increases steadily as throttle is reduced, going up into the 20s at idle. I'm mostly confused that the trends are so different. This selection is before/after the N52/0.15mm revolution, so is the tech involved somehow? Why would a torquier motor pull more amps at the low end?
I suspect that it is actually an error in the data for the Cobra motor. That was one of the first motors I tested, and the test gear has changed a lot since then. The typical efficiency curve of a brushless motor is a drop at very low throttle then a quick rise to peak efficiency then a drop as it nears high throttle. The fact that Cobra departs so dramatically from that curve seems to say there is something wrong with the data. I would compare against a larger sample of motors to get a better idea. If I get a chance, I may try to re-run that Cobra, just as a comparison point.
Looking closer at the data, the Cobra was on the old current sensor that was a shunt sensor, rather than the hall effect sensor I am currently using, so the in particular the low current accuracy is quite different, the current readings below about 1.5 or 2A aren't really comparable unfortunately. It's fairly accurate above that though, so it should be comparable above 3A.
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quadmcfly:
Nov 11, 2017 at 10:22 PM
Can you give me some specific examples of what you're looking at? I typically look at around 400-600g of thrust because that is the typical flying range for a motor.
Colin Hamilton:
Nov 11, 2017 at 11:14 PM
The cobra 2204 http://www.miniquadtestbench.com/2300kv-shootout-cobra-2204-2300kv-motor.html
and the RS2205S http://www.miniquadtestbench.com/emax-rs2205s-2300kv.html
Ok, knowing to look at that thrust range is good to know, thanks for the tip. In that case the difference is much less pronounced but still definitely there. What I'm most confused about is that (in any case) the trends in g/W as thrust decreases are completely different. Is the explanation in the differing levels of motor tech?
Thanks for the quick reply.
Colin Hamilton:
Nov 13, 2017 at 10:36 PM
Thanks for the quick reply. I'm sorry this is belated, but I think I messed up on my original the day of, or it got lost in the system or something.
The 400-600g rule of thumb is good to know, thanks. At that point the difference is smaller but still definitely there.
I'm looking at the EMAX RS2205S and the Cobra CM2204, on the 4x4x3 for comparison. But the trends hold true for most of the props.
The EMAX stays roughly around 3g/w for most of the throttle band, except idle where is goes down around 1. The cobra starts at around the same at top end and increases steadily as throttle is reduced, going up into the 20s at idle. I'm mostly confused that the trends are so different. This selection is before/after the N52/0.15mm revolution, so is the tech involved somehow? Why would a torquier motor pull more amps at the low end?
Thanks for your help.
quadmcfly:
Nov 15, 2017 at 11:02 AM
I suspect that it is actually an error in the data for the Cobra motor. That was one of the first motors I tested, and the test gear has changed a lot since then. The typical efficiency curve of a brushless motor is a drop at very low throttle then a quick rise to peak efficiency then a drop as it nears high throttle. The fact that Cobra departs so dramatically from that curve seems to say there is something wrong with the data. I would compare against a larger sample of motors to get a better idea. If I get a chance, I may try to re-run that Cobra, just as a comparison point.
quadmcfly:
Nov 16, 2017 at 10:04 AM
Looking closer at the data, the Cobra was on the old current sensor that was a shunt sensor, rather than the hall effect sensor I am currently using, so the in particular the low current accuracy is quite different, the current readings below about 1.5 or 2A aren't really comparable unfortunately. It's fairly accurate above that though, so it should be comparable above 3A.