[erlyrisa]

Hi - haven't been here for a long time...

I am building a new machine (my other one was just a test... to see if I got the idea)

-The machine I am building will require 2 steppers on either side of the Gantry... running in sync!! -this way I don't have to build a connector or have to run that connection along the bottom under the table. (an axle or a belt)

--wondering if anyone has done this or figured out how to do the electronics to sync the motors - preferably on 1 controller.

__.Yes I could just 'double up' the output from the step dir pulses to two seperate drives, but of course the problem lies in the 'lost steps' - which may arise.

-if it were propper servos then I guess I wouldn't have problem.

Some of the things I was thinking about:
A
1 controller - two motors,
-'bridge' the motors in a way that, when one loses a step, the other loses it too? -eg. whatever current spike is in one motor get's translated to the other?
B
2 controllers, two motors + encoder....
the differenec though with traditional servo system would be that the encoders would count a 'difference'between the two motors, the encoder that senses lag would 'block' the step single in that motor untill it is running intune with the other motor... electronics would be a simple comparator, blocking the step signal.
C
Same as in B, except the block would occur on the actuall drive current.


D
-Turn them into servos - yeah I could just buy some new motors.

or E --don't worry - I won't lose that many steps, and if I lose one in one motor the balancing forces in the gantry will probably soon bring the motors back into equilibrium. (hopefully centre of G is not skewed , biasing a lean in the gantry)

[b25hf4u]

Requires some fancy programming but B is doable so is C all others are dangerous, because your step error will become cumulative and eventually drop your Y axis!

The low cost solution is an overhead gantry with a shaft and sprockets on each side. Works best and is used on machine for example on a 20'x30' CNC cutter I used to run. Worked great until somebody hit Y with forklift! Always fun to rest that when it happens

[erlyrisa]

I was on the TurboCNC forum asking the same question.... and some one said don't worry about it... as long as I am under about 25% of total stepping power I won't lose steps.

--I have some 7amp controllers...

I am starting to think all I have to do is wire the two motors into the one controller....

the coils that get energised should 'balance' the currents being created, the only electronics that I could put in to help things along are some diodes to stop any reverse currents flowing across to the other motor?

[b25hf4u]

That may work, just another tip is to wire length the same,

[Torchhead]

Never wire two motors to one controller. You will buy yourself cross conduction problems (motors are generators too) and it will negate any anti-resonance control your drive might have. Microstepping will be a problem as well. No two motors are identical and the currents will not balance. The motor with a slightly lower impedence at the PWM frequency will draw more current. Motors can vary 5% in position by spec. Microstepping tries to sum vector currents to arrive at a position that is in between poles....Only problem is that the currents won't sum right with two coils on different magnetic structures in parallel.

You can easily drive two motors in sync with two motor cards by:

Driving both motor cards with the same step & dir signals. You have to make sure that you have enough drive to provide double the current. Good buffered BOB is suggested.
OR

Run each drive off it's own step & dir and "slave" them in the software. MACH has had this feature since MACH1. It works for either steppers or servos.

If your motors lose steps then you have other problems. Properly setup motors running inside their torque curve limits won't lose steps.

I have been running a plasma cutter with dual servos and MACH in slave mode for over 4 years. Each side has it's own home switch and the REF move automatically squares the axis if need. Seldom does it ever need it.