Hardware Selection Step-motor Control

[tiho]

Hi

I would like to control step-motors. I have a hardware driver for control but I need digital outputs for direction and start/stop of the hardware driver. May I use NI USB-6501 (24-ch, 8.5 mA) or myRIO?

Regards

[Zody]

Hi tiho,

To be able to provide some advises, we would need more details about the HW you have currently available.

What type of driver do you have? 

Best regards,
IR

[tiho]

Hi

For step-motors control I use A4988 driver:

http://www.robotev.com/product_info.php?cPath=1_39&products_id=311

https://www.pololu.com/product/1182

Regards

[Zody]

Hi tiho,

I had a look through documentation but I couldn't really find the specification for direction pin.

As a general description of the HW is that is TTL compatible, from here I can assume that NI 6501 should be sufficient for you to control it.

Unless you find explicetely the voltage level and the current needed, is difficult to confirm it.

Best Regards,

IR

[tiho]

Hi

Thank you for your answer. I tried with NI PCI-7833R and it was working. I suppose that with NI USB-6501 it will work too.

Regards

[BruceAmmons]

The problem with the usb 6501 will be speed.  Your program will have to toggle the outputs on and off.  You can't use a counter to output a pulse stream with the 6501.

Bruce

[tiho]

Hi

Thank you for your answer. What do you think about Labjack U3-LV. Is it usefull for step-motors control with A4988?

Regards

[LabJackSupport]

With the LabJack U3, if you use software to command each digital output transition (output-high or output-low), consider that it takes roughly 600us for each command-response per Section 3.1 of the U3 User's Guide.

There are a couple other ways to send pulses from the U3.  You can use the WAIT technique where you send a bunch of commands (high-wait-low-wait-high-wait-low ... and so on) to the device in 1 packet, or you can use a timer to generate output pulses via hardware timing.  The timer pulse output can be continuous, or you can use another timer to stop the output after a specified number of pulses.  See more in our Waveform Generation Application Note.

[LabJackSupport]

One detail, is that the logic high input level of the A4988 is 0.7*VDD.  That means if you power it from 5 volts, it might not be compatible with the 3.3 volt output from the U3's digital output.  The chip needs 8mA max from the logic supply, so I suggest you use a DAC (analog output) line to provide a lower VDD.  If you set DAC0 to 4.0 volts, and draw 8 mA, you will be left with ~3.6 volts which will work great.  Use "config defaults" in LJControlPanel to set the power-up default of DAC0 to 4.0 volts.

[tiho]

Hi

Thank you for your answer. In other words it is better to use Labjack U3-LV with A4988 or you can propose another hardware?

Regards