how to multiplex motors?

[srinivas_p]

i want to control 5 motors using 7344. Two of the motors can be multiplexed, since no situation arises where i need to control both of them. how exactly do we do it?

[Brian F.]

Hello. The 7344 is only able to control 4 motors at the same time. However, if two of the motors never will be used at the same time, there is a way to throw another motor into the mix. First, this procedure will only work if the motors that you wish to hook up to the same channel are one open stepper motor and one servo motor. If this is not the case, my recommendation would be to upgrade your board to a 7356 or the 7358 which has 6 and 8 axes respectively.

If your system meets the requirements mentioned previously, please view the pinout of the 7344 on page 5-2 at:

http://www.ni.com/pdf/manuals/370838a.pdf

From here, you can connect your stepper motor to the Axis 1 Dir and Axis 1 Step since the stepper motor only needs direction and step commands. Then, you can connect the servo motor to the encoder pins as you normally would and also use an Analog output pin as your DAC.

Basically, you can hook up a servo and an open stepper on the same channel as long as they are not being operated at the same time. The connections for the two motors are the same as if the other motor wasn't on that port since they don't share any of the same pins.

[Jochen]

I just want to add a comment to this:
For the case that all motors are of the same type you could think of using an external relay multiplexer to route the signals to multiple drives but this would mean a considerable amount of work, cost and potentially trouble so I wouldn't recommend this solution. For this case a board with a higher number of axes would be a much better fit.

Best regards,

Jochen Klier
National Instruments Germany

[abhiram]

this may seem to be silly question. but why does it take a considerable amout of time? i am planning to use the digital i/o pins as control signals

[Brian F.]

abhiram, I am sorry, but I don't completely understand your question. What is 'it' that takes a considerable amount of time.

[abhiram]

by 'it' i meant " using an external relay multiplexer to route the signals to multiple drives". the idea i have is to multiplex both the step signal and direction signal using one of the output from digital i/o as the control signal.

[Jochen]

If time matters is always a question of relation. If you have to bill each working hour that you spend on a project the time that you need for the additional cabling, programming and error checking when using the external relay multiplexer might be more expensive than buying a board with more axes.

For the case that you just need to route a step and direction signal the external multiplexer might be ok but if you have to use limit switches, inhibit signals and more advanced security features like the +5V host interlock and so on, things might become more complicated and you could easily end up with a more fault-prone solution that is even not cheaper than another board (if you have to calculate the time that you have spent on it...).

These are just some concerns that I derive from my almost 10 years experience with customer projects.

Jochen