Re: [CAD_CAM_EDM_DRO] Two motors on one axis EMC

Lars Levin wrote:

> Hi Group!
>
> I am planning on building a large Gantry 3 axis mill
> and have to use two motors on X-axis, and maybe
> also for the Y-axis.
> Is there a way to configure EMC to run two servos
> for one axis in a master slave combination?
>
> I am also preparing this 3-axis machine to add
> a 2-axis rotary spindle, to get 5-axis motion.
> If I need 2outputs for X, and 2 for Y and one for Z
> plus 2 for the head, a total of 7 motors,
> Is EMC limited to 6 axis or can I configure 7?

As I understand it, EMC can run 6 motor outputs from the parallel port
(2 pins each, step/dir), to do XYZ and ABC axis.

If you're doing servos, a Servo-to-Go card (which is EMC-compatible) can
drive up to 8 servos. I do not think, however, that it would easily
allow you to master-slave a pair of motors. Since I do not use servos,
I cannot perfectly advise on this.

What I would suggest doing, if you must use two servos off the same axis
output, is use EMC as a stepper system, and take the axis output to
drive two Gecko drivers. Gecko makes a servo driver that takes the same
step/dir pulse stream as a stepper driver, but instead runs a brushed DC
servo. A parallel-port breakout box/card would let you divert the axis
outputs to any number of motors, provided you have the drivers.

I cringe when I think about trying to sync two servomotors, because each
motor had it's own feedback loop. For myself, I would use a
long-distance mechanical coupling between two leadscrew, such as a
precision timing belt, and have the motor turn both using the belt.

There are other issues, such as alignment/racking of the gantry when
driven by two motors, synchonization of the motors and leadscrews, and
the cost of each possible solution.