When driving the Y axis....

[Jkountz]

This may seem like a silly question but when driving the Y with two steppers, one on each side, do you need another driver for that fourth motor or can you chain the two together? Naturally if you use one driver for both motors one would have to run in the opposite direction. How is this usually done?

[Jack000]

driving two motors with one driver is not a good idea. You should use one driver for each motor. The inputs to the drivers may be connected together, and the stepper wires reversed on one motor will give it opposite direction. Or you can wire both steppers the same way, and deliver matching opposite inputs to the drivers through software (there should be an option in your cnc software that does this)

[MyCattMaxx]

I'm a noob but wouldn't you only have to run one in reverse if you were using R&P for duals?

[CarveOne]

Originally Posted by Jkountz This may seem like a silly question but when driving the Y with two steppers, one on each side, do you need another driver for that fourth motor or can you chain the two together? Naturally if you use one driver for both motors one would have to run in the opposite direction. How is this usually done?

No, it's not a silly question at all.

The proper way to do this is to have an individual driver for each motor and use the settings in Mach3 Ports and Pins menu to slave the A axis (fourth axis) to your Y axis and to reverse the A axis motor. The drivers can be on one circuit board layout or a separate module like the Geckos. [On my machine I reversed the phase B coil wires on my A axis motor so that this motor setting in Mach3 is the same as the X axis.]

If you just parallel the input wires to the two drivers the signal level may be too low to properly operate either drive input. It depends on the driver input circuit design.

If you parallel two motors on one driver output it is very likely to damage the driver output device.

CarveOne

[asuratman]

Hello,
I bought dual drive from Granite Device http://granitedevices.fi/index.php?q=products for my plasma, 2 ea dc servo motor using 1 ea drive. I am building now. So total using only 2 ea drive. My purpose here is just for simplicity but I need power too. I use 4 ea 1125 oz in kelling motor on all axis.

[mlabruyere]

Originally Posted by CarveOne If you parallel two motors on one driver output it is very likely to damage the driver output device. CarveOne

Yeah...since that would double the AMP draw the driver sees....right?

[RomanLini]

No, normally the driver will limit current to the same amount, but with 2 motors connected they will only get half the required current each, so they won't work very well.

Also the motors can produce different back-emf as they operate which can confuse the driver and cause weird operation and possibly driver damage.

[mlabruyere]

Gotcha....thanks.

In the RC world I've seen guys run 2 brushless motors from 1 ESC and it works sometimes...other times one will start and the other will sputter and quit or fry.....

[Jkountz]

Thanks everyone, that clears things up for me. I have been wondering about this for some time now!!

[CarveOne]

Originally Posted by RomanLini No, normally the driver will limit current to the same amount, but with 2 motors connected they will only get half the required current each, so they won't work very well. Also the motors can produce different back-emf as they operate which can confuse the driver and cause weird operation and possibly driver damage.

If both motors are getting the pulses at the same instant the current drawn from the driver can be double, but that in itself is not a problem if it is not above the rated output of the driver. If pulses to the motors are not synchronous, the current drawn from the driver can be anything from almost none to the total current of both motors. Some driver circuits have no protection from opens, shorts, or excessive current loads and I doubt that they handle back EMF situations very well either.

Unless you know for sure that the driver design you have is able to work with paralleled motor wiring it is not a good idea to just wire them and see what happens. Unless you are willing to lose an otherwise good driver board.

CarveOne