Re: [CAD_CAM_EDM_DRO] Anaheim

rocketscientistnate wrote:

>Is anyone here familiar with Anaheim? (www.anaheimautomation.com) I
>looked through their products, but their price list is being updated
>and is currently unavailable. I know they'll be more expensive than
>Gecko's, but it seems like a lot of the little lizards have been
>burning up lately (just from reading these messages). Most of the
>Anaheim driver's have motor miswiring protection built in. They
>even have a stepper/driver combo built together in the same case,
>just a cable to hook your pulse generator to. I was about to throw
>out my old Boss 5, but I think you guys have convinced me to go with
>Geckos or at least something similar. Did I understand right that
>geckos only use 2 of the 4 windings? How does this affect its
>performance? I'm probably wrong, and I know it does work, but this
>doesn't seem like the "correct" way to make a machine run.
>

The old way was using what are called "L/R" drivers, the ines with the
huge vitreous-enamel 100 W resistors in them. They only needed 4 power
transistors, and the transistors and driving circuitry was expensive.
The performance was abominable, and you were lucky to get 500 RPM out
of them. Bridgeport came up with a tricky adaptation using a saturable
reactor to replace the resistors, and they got decent performance partly
with that and partly by the use of massive motors. These are both
variations
of unipolar drivers.

Now, transistors are cheap, the driving circuits even cheaper. The
Gecko uses
8 transistors to provide bipolar drive to the windings. That means the
current
will go either way through one winding, instead of one way only through each
half of the winding. One of the interesting results of the bipolar
drive is the current
flowing in the winding when current reversal is needed is that current
is pumped
back into the power supply, instead of being burned up in the drive.
Only the
most sophisticated unipolar drives ever tried to recycle that energy.
The faster
you go, the more significant this becomes.

Note that the unipolar drives only use half of the winding at any time.
With a bipolar
drive and an 8-wire motor, you have the choice of full winding in
series, half winding
or both halves in parallel. The later option is one of the best, BUT it
requires VERY
careful wiring of the phases. Any mistake in the wiring can burn up
many drivers,
not just the Gecko 201. Of course, a fuse in the DC power input might
well have
saved the Gecko in question. The problem with the full winding in
series is the
increased inductance, which can reduce the maximum speed.

Jon