motor rotation sensor

[stegla]

I wish to use a brushless outrunner in a freeflight model. Should the motor cease to rotate i.e. in a crash I want the power to the motor to be cut.

I will be using a PIC to control/time an ESC to drive the motor.

Now then............How can I get some sort of digital signal that can go to an i/p of the PIC that will sense whether the motor is turning or not?

I have in mind maybe a Hall device and program the PIC to test for the edge of a pulse?

Any thoughts?

Cheers
Steve

[jeffs555]

Don't know for certain, but I would think that a good brushless ESC would stop power to the motor if the prop became blocked so the motor couldn't rotate.

[Malc C]

Also, if you use a gearbox with nylon gears then there would be some safe guard in that the gears would strip if the prop got fouled and the motor was still being powered. The other thing you could try is fitting a resettable fuse in the supply line from the battery to the ESC. If its rated as slightly more than the continios current it schold cut in if the ESC draws more due to a stalled prop

[Dan Baldwin]

You could put 2 small magnets on the shaft 180 deg apart to maintain balance, put a hall effect sensor that will be tripped by the magnets, and monitor the hall effect sensor with a microcontroller. If the throttle was above a certain level (perhaps 5%) and the microcontroller doesn't see a pulse for a certain length of time, the microcontroller would shut down the throttle.

Dan

[AndyKunz]

You could put a small LED or photodiode (an LED will act like one) to catch the blinks as the prop passes in front. Lighter than having magnets on a spinner.

I have a multi-channel servo sequencer/timer that might be of interest if you have a more-advanced FF model. E-mail me andy@montanadesign.com for details. Several of the top US CL guys are using them in the E-C/L planes.

Andy

[stegla]

Guys

I have messed with resettable fuses and found them unreliable. My max current varied widely depending on the state of the Lipo (charge, temp, age etc.)

This application is for FF scale so I am leaning towards a hall-effect device. Also some extra electronics in the nose is better than the ballast that all scale models seem to need.

Also I am thinking maybe of an astable that is triggered by the pulse from the hall-effect device so that over 100rpm? the pulses merge into a continuous high that can be monitored from a PIC i/p?.................this should be easy to implement?
My PIC programming skills are basic as is my electronic design so it'll have to be kept simple.

Andy, your controller sounds interesting. I'll email.

Steve

[Dan Baldwin]

Guys

I have messed with resettable fuses and found them unreliable. My max current varied widely depending on the state of the Lipo (charge, temp, age etc.)

This application is for FF scale so I am leaning towards a hall-effect device. Also some extra electronics in the nose is better than the ballast that all scale models seem to need.

Also I am thinking maybe of an astable that is triggered by the pulse from the hall-effect device so that over 100rpm? the pulses merge into a continuous high that can be monitored from a PIC i/p?.................this should be easy to implement?
My PIC programming skills are basic as is my electronic design so it'll have to be kept simple.

Andy, your controller sounds interesting. I'll email.

Steve

If you're going to use a PIC, you won't need a monostable (one shot). You should be able to come up with a circuit that doesn't need a PIC using a re-triggerable one shot and a FET.

Dan

[stegla]

If you're going to use a PIC, you won't need a monostable (one shot). You should be able to come up with a circuit that doesn't need a PIC using a re-triggerable one shot and a FET.Dan

Dan,
Thanks, yes I meant a one-shot monostable. The PIC is essential and is already quite busy generating the 1ms to 2ms pulses to drive the ESC and to time the length of flight and throttle-setting. To test an I/P for a hi or lo would be dead easy to add to the program.

Steve