Mode Zero

This appeared on a home-brew radio forum I peruse. I assume it was a motor with brushes. Has anyone here experienced or heard of this before?
All the best,
geary

You can use a normal brushless motor as a DC generator by connecting six diodes to rectify the three phases into DC: you have a pair of diodes connected to each motor wire, one diode of the pair has its +ve facing the motor and the other has its -ve facing the motor - then you join the three free +ve diode leads together and that's your +DC, similarly the three free -ve diode leads are joined to give the -DC or GND.

I don't know if a normal brushless ESC would work that way - it's something I've never tried.

Thank you for your reply Martin, very interesting!

I've experimented in years gone by with using a a brushed motor as a crude DC generator. I also have a vague recollection of a magazine (Elector?) publishing an article for a DIY anemometer using a speed 400 size motor, where voltage generated indicated wind speed.

From the reference to "...many years ago..." I'd guess it was probably a brushed motor. Given that most brushed ESC's had a diode across the motor terminals (for spike protection?), it could have been a crude 1/2 wave rectifier, although if so, I'm surprised it generated enough current to drive the servos.

Mike and I recently discovered a bug (feature?) in my solar powered plane controller that shows that at least some brushless motor and ESC combinations will work as generators.

The solar controller remembers the highest supply voltage it's seen so that it can throttle back the motor when not enough power is available. We found that when powering the system with solar cells the maximum voltage seen by the controller could sometimes be recorded as higher than what the solar cells ever deliver. We found that this happens when rapidly throttling back using the transmitter stick.

It seems that the motor/propeller, acting as a flywheel when going faster than the ESC is asking for, dumps energy back into the battery. With a real battery you don't see any voltage rise because the battery is just briefly recharged (like regenerative braking on an electric car), but the solar cells can't accept a reverse current flow, so the voltage briefly rises.

We fixed the unwanted effect on the solar controller by altering the program to only remember the maximum voltage seen during the first few seconds after start up.