Alt-BEAM Archive

Message #03392



To: Wilf Rigter Wilf.Rigter@powertech.bc.ca,
From: Wilf Rigter Wilf.Rigter@powertech.bc.ca
Date: Wed, 19 May 1999 13:15:59 -0700
Subject: [alt-beam] Re: Drive cct for these MicroMo's?


Hi Chiu,

I tested my "theory" for using a TriCore with a 3 phase brushless motor
which is slightly different (grounded Y) from the MicroMo motor ( ungrounded
Delta) but uses the same basic principle. Both a 3Nv MicroCore and a
3NuRing with suitable "half bridge" outputs are suitable for driving
brushless motors. The NuRing is more efficient in that it produces 3
symmetrical squarewaves phased exactly 120 degree apart and has a average
zero DC current component. On the other hand, the MicroCore is easier to
adjust for speed. The square wave outputs were buffered with 3 complementary
output stage which seemed to work best using a 5V supply with 20 ohm
resistors inserted in the emitters turning the bridge into complementary
current sources. This has the added advantage of providing current limiting
to about 200ma in the event of a dead short on the outputs.Without testing a
sample of the MicorMo it is not possible to guarantee these circuits will
work but I would say there is a high probability that it will be successful.
Of course a full digital MicroMo variable speed brushless motor controller
with crystal time base and serial link is but a "Stamp" away (but it's not
BEAM!)
Next I will design and test a simple, variable speed, reversing NuCore
circuit and report back with the results including some nice schematics and
waveforms..

enjoy

Wilf Rigter mailto:wilf.rigter@powertech.bc.ca
tel: (604)590-7493
fax: (604)590-3411

> -----Original Message-----
> From: Wilf Rigter [SMTP:Wilf.Rigter@powertech.bc.ca]
> Sent: Tuesday, May 18, 1999 5:40 PM
> To: 'Chiu-Yuan Fang'; BEAM List
> Subject: RE: Drive cct for these MicroMo's?
>
> Yes, I am sure something smaller and simpler can be cooked up. You can
> think
> of this type of motor as a tripolar stepper =) As a first approximation
> (and
> to keep it Beamish), I would use a fixed frequency 3 phase triangular
> waveform perhaps using 3 emitter-follower half bridge circuits with the
> signals derived from the bias points of some kind of TriCore (NuRing?).
> AFAIK just swapping 2 of the 3 drive signals will reverse the rotation.
>
> Luckily I have a similar (but somewhat larger) 3 phase brushless motor
> with
> external drive so I can try this idea out. I suppose that it is also
> possible to use the more conventional method of 3 Hall effect devices
> surrounding the motor body to pick up the rotating magnetic field from the
> rotor or an encoder wheel on the output shaft with 3 optical sensors and
> use that signal with buffered outputs to drive the windings.
>
> Now designing solar racer and getting good traction at 100,000 RPM will be
> left as an exercise for the student =)
>
> I'll try the first approximation and will report the results.
>
> regards
>
> Wilf Rigter mailto:wilf.rigter@powertech.bc.ca
> tel: (604)590-7493
> fax: (604)590-3411
>
> > -----Original Message-----
> > From: Chiu-Yuan Fang [SMTP:chiumanfu@home.com]
> > Sent: Tuesday, May 18, 1999 3:50 PM
> > To: BEAM List
> > Subject: Drive cct for these MicroMo's?
> >
> > http://www.micromo.com/1.99COMBO.pdf
> >
> > Here's some specs:
> > 9mm long x 2mm dia.
> > Speed varies with AC frequency
> > 0.5VAC
> > Non-reversable
> >
> > Anyone know a smaller drive circuit that can be used to control these
> > little
> > gems?
> >
> > --
> > Chiu-Yuan Fang
> > chiumanfu@home.com
> > ICQ=5614919
> > http://www.geocities.com/SouthBeach/6897/beam2.html

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