controlling more than 4 motors simultaneously using 7344

[srinivas_p]

Is there any way of controlling more than 4 motors by using a multiplexing scheme. or can it be done in any other way.

[Buechsenschuetz]

It might be possible to control more than 4 drives with a single 7344 by multiplexing ALL control and feedback lines. The digital i/o lines migzht be used as control signals for the multiplexer.

Anyhow, this solution is not very convenient and will work only if the drives of one group all have the same parameters. I think it would be a better solution to use NI's cards for controlling 6 or 8 drives.

[Jochen]

The 7344 supports four motors (servo or stepper) simultaneously. As long as you are using stepper motors you could also think of switching the motion signals with an external relay multiplexer to more motors but then the multiplexed motors couldn't run in parallel. Depending on your application this would mean that you would have to switch a lot of signals (step, direction, limit switches, inhibt outputs,...) and I don't think that this would make much sense. With servo motors this approach wouldn't work anyway as the control loop would be interrupted.

If you want to control more than four motors you better should use another PCI-7340 (2 or 4 axes) or a PCI-7350 (2, 4, 6 or 8 axes).

Best regards,

Jochen Klier
National Instruments Germany

[srinivas_p]

i am a student working on NI motion controller. so it is not possible for me to get another card. neway since all the motors i am using are stepper motors i am thinking of multiplexing as a viable option. What are the other practical difficulties other than controlling the motors simultaneously?

[Jochen]

With open loop steppers you shouldn't expect too many problems but in any way you should use high quality components that don't have an impact on the contol signal qualit. Of course this solution means a considerable amount of work but if time doesn't matter you should be able to do it. You could use the digital output signals on connector #2 of the 7344 to control the external multiplexer.

Jochen