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Electric Stunt => Gettin all AMP'ed up! => Topic started by: Mike Alimov on February 25, 2020, 05:04:09 PM
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I'm posting this for informational purposes only. What you see on this picture is an actual current (not voltage!) waveform that drives one of the phases of an electric brushless motor. (Details: motor Atlas AM2909/20; ESC: Castle Thunderbird 36; load: Taipan propeller 9-4, battery: 3S; RPM: did not capture; throttle control via Spektrum DX8 radio; waveform captured by Keysight CX3324A waveform analyzer with CX1104 differential current probe). Frankly, I'm not impressed with the waveform, but there is only so much we can ask of a hobby-grade sub-$100 ESC. With a more efficient drive scheme, we could probably reduce battery consumption by 30-50%, and thus bring the overall weight of the electric powertrain on par with the combustion setups.
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Mike,
What in the waveform is unimpressive to you? "Inquiring minds need to know...."
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I doubt that anything you change in the ESC will give you 30% - 50% efficiency increase.
Main problem is that we don't use very efficient design for our motors, geared in-runners can be in the high 90% range, versus low 70's for outrunners.
Having said that, you might find this interesting, these guys were working on a solar powered, continuously flying UAV, so needed high efficiency at part throttle.
There used to be a lot more info about this on line, but they must have decided not to give away all their secrets :)
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A triangular waveform like that causes about 33% more loss in the motor windings than a nice smooth constant waveform would -- but that's just loss in the windings, not bearing loss, or loss in the ESC, or iron losses in the motor, or inefficiencies in the batteries.
Making it more efficient means switching the ESC faster, which increases iron losses in the motor, and switching losses in the ESC -- you'd be lucky if you got any increase, but if you want to start making ESCs you're welcome to try. I'm pretty sure I'm not the only circuit designer on this forum; I'll certainly give you pointers (starting with -- start with a VESC and downsize it; don't mess around with rolling your own from scratch).
Alternatively, you could use external inductors to smooth the current. That would add weight to the system, and you'd have to custom-make an ESC to deal with the inductance (you couldn't just shove it onto an existing motor). Again, you're welcome to try.
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ESC designers and their companies are a very very competitive part of this universe
IF there was a definitive way to reduce battery consumption and or increase motor power or efficiency....those experts would be highly motivated ....I think
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ESC designers and their companies are a very very competitive part of this universe
IF there was a definitive way to reduce battery consumption and or increase motor power or efficiency....those experts would be highly motivated ....I think
It's a tradeoff. I suspect you could, but only at the cost of a heavier, bulkier, more expensive ESC. Whether the added ESC weight could be bought back with less battery -- I dunno. Even if you could, it'd be a hard sell.
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Mike,
the waveform current that you showed, is typical for reduced power operation. At full pulse length, the voltage is trapezoidal, resulting is less losses. That is the reason for me to select the propeller that absorbs the maximum power when needed.
Screenshot provided by Castle.
Regards,
Wolfgang
(https://myalbum.com/photo/7sHcWq8UWVay/540.jpg)