On Wed, Feb 15, 2006 at 06:21:49PM -0500, David VanHorn wrote:
> > I don't think that's the problem. The diodes are rated, individually,
> > for 2x more current than is the steady state.
> 
> 
> Only 2x eh.. So if the conduction angle is less than 90 degrees, you're
> there.
> I bet if you take that cap way down, and accept some ripple, you'll have
> your diodes living.

Hmm... So a 10000uF instead?

One tricky thing is I use the back emf from the stepper motors to act as
an encoders. The steppers are in a 8x8 grid and each stepper moves a
knob. The idea is that the knobs move on their own, and people can also
turn the knobs to interact. I use the back-emf as a cheap way of adding
in position encoders. It actually works very well, even though the
emf-pulse of someone slowly moving a knob is only about 5milivolts, but
the PIC's ADC can sense that just fine.

It does seem to be sensitive to noise in the power supply. The motors
are powered in a chains of 8 units connected by 22gauge wire. Stupid
yeah, but packaging constraints forced this. Each time one motor in a
chain starts moving, the rest sense it as back-emf. Once a motor is
moving it doesn't cause any further problems. A software fix was my
solution...

My worry is how well I can filter out that ripple. Of course... I use a
PIC+ADC to do the sensing, so I can probably fix that in software too.

-- 
pete@petertodd.ca http://www.petertodd.ca
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