Saturation in motors

The new control algorithm for AutoQuad flight controllers.

Re: Saturation in motors

Postby Max » Sat Apr 18, 2015 3:31 am

What's the all-up weight on that LB? Maybe time for some fresh props? ;) It's also top-heavy, which never seems to help in my experience. Is the CoG right on? A small shift can make a huge difference in how the tiny frames handle.

The motors will certainly wear out eventually (depending on a lot of factors), as will the cheap little batteries. At some point you're going to get saturation simply because there's not enough thrust to keep it in the air properly. I imagine the more aggressively you tune it, the shorter your flight times will get.

-Max
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Re: Saturation in motors

Postby Mullet » Sun Apr 19, 2015 1:15 am

AUW = 50g. This is with my largest, heaviest battery.

Have some fresh props and have 4 new motors on the way. Not sure if the center of gravity is right. It seems to me that since the bluetooth module has the pins hanging off that it wouldn't be perfectly center. I'm not sure how to measure CoG. I suppose I can run tests with new props and then one with new motors to see if this makes a difference.

Sounds like motors typically die slowly over time. I did have one motor burn out. You could smell a burned smell after it died. Is this more of brushed motor problem? Do brush-less motors die from general use as well?

Need to understand a bit more how this thrust stuff works. I understand it's based on prop/motor configuration, but that's about it.
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Re: Saturation in motors

Postby Max » Sun Apr 19, 2015 2:48 am

50g is pushing it with 7mm motors. It works, but that's about the practical limit, I've found, and that's with fresh motors and props and battery. I had trouble recovering from quick descents and wind gusts, at least until I used some bigger props.

To test CoG I just lightly pinch the M4 by opposite corners between two fingers. Or rest a pair of opposite arms on the tips of my fingers. Then check which way the whole thing leans. It should stay level regardless of which two corners/arms you grab. Not very precise, but it works. I'm sure it'd be pretty easy to make a rig to hold the little micro to check CG, but I've never gotten around to it.

Besides the physical damage potentials Larry mentioned in the other thread, it's the brushes that typically wear out on brushed motors. Obviously not a problem on brushless motors, which is part of their appeal. You could certainly still damage/destroy a brushless motor physically, but with regular use the only thing that can wear out on those are the bearings.

Roughly speaking, available thrust is a combination of motor spec (size/winding/magnets/etc), prop dia/pitch/efficiency, & voltage. As all those things wear down over time, the total thrust available goes down. An old battery for example might not be able to deliver the same voltage at a given load (current) as it used to when new. Brushes wear down and make less contact inside the motors, producing less power (and/or bearings get worn and produce drag). Props get chipped and warped, loosing efficiency.

-Max
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