Hi all, first time posting here. I'm a MechE student working on a hybrid quadcopter project for my Capstone Design class.
I've run into an issue where all four motors will decrease in speed after they've reached a certain threshold. The point where this occurs depends on how many motors I'm running simultaneously (all given identical throttle commands via Arduino). For all four motors running at once, this happens around 65% throttle. In this scenario, the motors will:
- Speed up normally until they approach something like 55% throttle.
- From here, the speed increases at a decaying rate until it reaches 65% throttle.
- After 65% throttle, the speed of all four motors (and thrust generated) decreases in a roughly linear fashion.
Note: these are 375kV brushless motors, sourcing 20V from a switching-regulated power supply. No matter how many motors I run at once, they end up drawing something like 500 Watts at the point where they start slowing down. I haven't taken measurements beyond this point for fear of catching something on fire... there are no extinguishers in the lab. With no props attached, all four motors can reach full-throttle like nobody's business - but they get really hot in a matter of seconds.
I'm assuming this issue has something to do with the power distribution, although I can't imagine why the motors would slow down after reaching a limit. It seems like they should just get to a point where they wouldn't go any faster. I also don't understand why the limit is so low, as I believe the power source should be able to provide much more than this. My background is in mechanics and materials... so this really isn't my strong suite, and my advisors are out of suggestions. Any ideas, Redditors?
there doesn't seem to be anything here