Never done thnis, just thinking...
One idea might be commutating bipolarily, not on-off.
And plus-off-minus-off-plus etc is for efficiency even better than=
 plus/minus

Like=20

L1: +++000---000+++000---000
L2: +000---000+++000---000++
L3: 00---000+++000---000+++0

Not seeing it clear though, it is very late here...

/Morgan

Hej Sean H. Breheny. Tack f=F6r ditt meddelande 00:42 2002-08-05 enligt=
 nedan:
>Hi all,
>
>One of the things I'm working on involves controlling brushless DC motors.
>As a first step to understanding them better, I built a three half-H bridge
>driver and I am trying to just get one of them to run, driven by my driver
>circuit. The motor I'm using is a Maxon EC45 with Hall effect sensors. I
>was under the impression that each hall effect sensor output simply told
>you what polarity to feed to it's particular winding (ideally, you would be
>feeding it with a sine wave but I think that a square wave should be close
>enough for a rough test if not for most applications). I.e., all I need to
>do with my three half H-bridge circuit is to connect each winding to +
>voltage when its hall output is high and to gnd when its hall output is
>low. When I do this, the motor runs, but at about 1/4 of the correct RPM
>and drawing about 40 times the correct no-load current. I have tried
>swapping the sensors around in every combination possible (i.e., use sensor
>1 to control winding 2, etc.) and even tried inverting all the hall outputs
>and then trying all combinations again. The best I can get is to have it
>run at about 1.5 times the correct rpm for my input voltage (!) drawing
>about 7 times the correct current.
>
>The motor datasheet does not describe how to do the commutation, and the
>info I have found on the web so far seems to vindicate my initial simple
>guess.
>
>Any ideas?
>
>Thanks!
>
>Sean
>
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