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The trick Bridgeport uses (pretty tricky, but not original) is to use a mag
amp on the AC input to the rectifier.

From: "Matt Shaver" <mshaver@...>

Sorry I haven't gotten back to you today, I've caught a bad cold and feel
like hell. I'm glad you got hold of Fred. I called him today too and he
briefed me on the discussion you had regarding your problems.

Hope you are feeling better. Hope Fred didn't mind my calling.

P.S. What do you think your max feed rate will be?

I think some where around 20 ipm is all I can achieve.

From: Jon Elson <jmelson@...>

Tim Goldstein wrote:

That is a good question and I don't know the real answer. From my
experience the input current draw is less than the total of what each

is set for added together (3 axis's set at 5 amp each draws less than 15
amp).

This is because a 'chopping' type stepper motor driver is really a special
case of a 'buck' (or step-down) switching power supply. So, the input
current (at higher voltage) is always less than the output current (at

voltage). So, if you are using a 5 V, 5 A stepper (that's 5 Amps for each
of 2 windings) and are in full step mode where both windings are always
energized, you have 5 x 2 = 10 A x 5 V = 50 VA or Watts out. If the
main power supply is 24 Volts, it draws I = P / V, or 50 / 24, or
approximately 2 Amps. Various losses in the chopper will cause the
current draw to be a bit higher. So, that is how 2 amps in can be turned
into 10 amps out.

That is a good question and I don't know the real answer. From my
experience the input current draw is less than the total of what each axis
is set for added together (3 axis's set at 5 amp each draws less than 15
amp).

From: Don Hughes <pencad@...>

Don;

These are unipolar motors

The two red wires are one winding and the two green wires are another
winding.
If you are going to run them in Bipolar mode then do not connect the
white or
black wires to anything as they are the center taps. To run them in
unipolar
mode you would normally connect the white and black together and connect
that to your power supply. The motors with the connectors cut off I used
for quite a while and I am sure they are ok. The motors with the
connectors
came out of working equipment so they should be good, but you never
know.
Let me know what you find out. No hurry though.

OK....that makes things somewhat clearer, as to how I will hook them up.

When checking the motors the resistance between the two green should be
between
8 to 16 ohms, one green to the center tap wire should be 1/2 the first
reading.
I can't remember the exact reading. Same goes for the two red wires. The
problem
is some multimeters do not differentiate between 6 ohms and 12 uhms to
well.

I must be doing something wrong on my end for checking. I get the same
ohms no matter what. Should I be holding some wires together and then
check..???. Bill, do you know what the red and green wires and their
tracers were for(eg. step and direction..etc)now that I know the black
and white are center taps.

Thanks again

Don

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Don;

These are unipolar motors

The two red wires are one winding and the two green wires are another
winding.
If you are going to run them in Bipolar mode then do not connect the
white or
black wires to anything as they are the center taps. To run them in
unipolar
mode you would normally connect the white and black together and connect
that to your power supply. The motors with the connectors cut off I used
for quite a while and I am sure they are ok. The motors with the
connectors
came out of working equipment so they should be good, but you never
know.
Let me know what you find out. No hurry though.

When checking the motors the resistance between the two green should be
between
8 to 16 ohms, one green to the center tap wire should be 1/2 the first
reading.
I can't remember the exact reading. Same goes for the two red wires. The
problem
is some multimeters do not differentiate between 6 ohms and 12 uhms to
well.

From: Don Hughes <pencad@...>

The four motors are set up with center tapped windings. An ohmmeter
should tell you which groups of 3 are connected to the same winding, then
a little more probing with the ohmmeter will tell you which lead is the
center tap. (The leads which have the most resistance of any combination
are the end 2 wires, the remaining one must be the center tap.)

Well I did this and all the wire combinations that passed the continuity
test have all the same resistance. What I have found out is that there
are two sets of red wires, one with a white tracer on it, and a black
wire that mate up. The other set is two green wires, one with a whit
tracer on it, and a white wire that mate up. But as far as ohms go, they
all seem to have the same, so finding the center tap is difficult. Any
other suggestions Jon?

Thanks again,

Don Hughes
Vancouver, BC Canada

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This is their web site....for info send em some e-mail.
Dave
<A href=">SKC- Stepping Motors</A>

The four motors are set up with center tapped windings. An ohmmeter
should tell you which groups of 3 are connected to the same winding, then
a little more probing with the ohmmeter will tell you which lead is the
center tap. (The leads which have the most resistance of any combination
are the end 2 wires, the remaining one must be the center tap.)

From: "Tim Goldstein" <timg@...>
I called Fred today and he istructed me that for the steppers the
OUTPUT_SCALE parameter is not used. His explaination is that it relates

the feedback from a servo and from what I think I understood a "-" value
here would reverse the direction of error compensation from input off the
encoders.

To change the direction the motor moves Fred told me to put the "-" in

INPUT_SCALE entry as this controls the direction the motors move from
controller input.

Reduce the DEFAULT_VELOCITY, DEFAULT_ACCELERATION, MAX_VELOCITY and
MAX_ACCELERATION parameters. Velocity is in inches per second and I

acceleration is in/sec/sec. I would think a velocity of 1 and an
acceleration of .1 would be a starting point for you (this is a guess).

Feedback from Fred seems to indicate that right now the DEFAULT_VELOCITY

hard coded in Xemc and this parameter is ignored. He said he would

an updated version that will read this parameter and put it on the FTP
server.
The MAX_ACCELERATION parameter is not used at all as gcode has no

to override the default acceleration, but Fred's suggestion was to set it
the same as the DEFAULT_ACCELERATION.
The MAX_VELOCITY figure should be what you get if you do a "G0" rapid

but in my playing so far I am not sure if this value is being

Fred was going to take a look into it.

The four motors are set up with center tapped windings. An ohmmeter
should tell you which groups of 3 are connected to the same winding, then
a little more probing with the ohmmeter will tell you which lead is the
center tap. (The leads which have the most resistance of any combination
are the end 2 wires, the remaining one must be the center tap.)
These motors can be used with the half-winding drive, and 4 transistors
for the whole motor. You put the DC supply through a resistor to the
center tap. Ignoring the center tap, you can drive these motors with
2 full bridges, from the winding ends. This takes 8 transistors, but
gives better torque, and higher speed.

The other motor has 4 separate windings. This is just a bit harder to
decipher, but it has 2 pairs of 2 windings. These can be set up as
center tapped, parallel, or series. Running them parallel, with 2 full-bridges
gives best torque and speed. That could add up to more power than
your driver can put out, although that would only be 2 amps/winding
in parallel. You probably have to drive the coils one at a time, and
by finding which connection nulls out current in another winding, you
can determine which 2 windings are the pairs, and which way they are
polarized.