searching a brushless DC startup procedure

Hello,

if you have a look to a modern brushless controller for radio controlled flying models you can see

- that the motor has a very short startup time until the right moving (about 100-200ms)

- that no initial alignment for a known position is done

- that a backward rotation only about 30 - 60 ms after starting is recogniced and the motor is running in the right direction

- that because of the used 8 bit Microcontrollers there is no extrem complex algorithm possible

- that the controller works probably in voltage controll

Does anywhere have information about the used startprocedure or a webside/usegroup where mor information is available?

Best regards

Endrophie

Reply to
endrophie
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You can use a technique known as "six stepping" to get the motor up and running. Once it has some momentum, the switching transistors are synchronised to the shaft position either using Hall Effect sensors or by monitoring back emf e.g. using a microcontroller with built in A-D connverters. This is electronic commutation.

I recently built a very simple six-stepping controller for a 3-phase brushless DC motor taken from an old hard drive using a 74HC164 shift register and 74HC132 quad schmitt nand. One of the nand gates was a variable frequency RC oscillator acting as the speed control.

The pull-up / pull-down transistors must be driven as follows :

pull ups (1 = on) Phase1 = 110000 Phase2 = 001100 Phase3 = 000011

pull downs (1 = on) Phase1 = 000110 Phase2 = 100001 Phase3 = 011000

The motor will only start from stationary if the speed control is set to minimum. The speed can then be increased fairly rapidly but not too quickly or else the motor will stall. I haven't tried the back-emf stuff but I know that's how it's done e.g. on

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Reply to
Andrew Holme

Hello,

ste controller must work in sensorless mode. The problem is, that when you have a very slow rotation speer, the BEMF has a littly amplitude. And if you a starting sequenze to the motor, it should rotate reliable in the right direction. So it must be possible to detect near zero speed the direction and the rotor position (but without any strategies who need the current).

Best regards

Endrophie

Reply to
endrophie

when

reliable

Six-stepping works reliably at low speed without feedback. The six-step sequence dictates the direction of rotation.

strategies

What else can you measure apart from voltage and current? You would need to mount a sensor on the shaft.

Reply to
ajholme

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