USB 6008 for stepper motor

[svijay]

Hi friends

I am going to do one project in labview

my requirement is to control the stepper motor in following way

while pressing one button in front panel  the stepper motor should run in one direction in  less than 30 RPM continuously.

 I have seen in USB 6008 specification we can only send digital I/O at 20mA.

But, my application require minimum one kg -cm torque, for that the stepper motor that I am having will draw more than 20mA...(probably 0.5 to 1 A)

and I don't know what exactly the stepper motor driver will do...

Can anyone elaborate the function of stepper motor driver ...?

Can stepper motor driver amplify the current pulses (digital output) to produce required torque?

i want to achive this with usb 6008

[SteveP]

For less than the cost of the 6008, you can purchase a stepper motor controller and driver that accepts high level text commands sent by RS232 seial (or PIC) to control its motion and parameters.  One example is

http://www.stepperboard.com/

[svijay]

Thank u for your reply Steve

my project is not ended with previously mentioned steps..

I however need to purchase usb6008 for my project .

Because it requires to get feedback from some sensor also and I have to process lot of data... So controlling stepper motor is not only my problem

any way thank you for your reply

can u explain what exactly the stepper motor will do..That is whether it will amplify the digital outputs from 20mA 

[johnsold]

A stepper motor driver usually consists of power switches (or more complicated circuitry) to drive the motor windings to the ampere level currents required.  The inputs to the driver may be as simple as a pulse for each step or a motion profile covering acceleration, velocity, and distance.

The biggest issue with using the 6008 is its slow digital output rate ( <150 Hz, software timed).

Lynn

[svijay]

in what way the 150Hz affect the stepper motor funtion... wether it will affect RPM or something else..

[johnsold]

It limits the maximum rate at which the motor can step. Suppose that you have a 200 step per revolution motor. If your motor driver moves the motor one step per pulse and you are generating the pulses from a digital output line on the 6008, then you can generate no more than 75 pulses per second (less than 23 rpm).

Lynn

[craigp]

Another good source for stepper motor drivers is AllMotion.  www.allmotion.com

They sell stepper motor drivers that can be used with simple serial commands.  If I recall correctly, they have a LabVIEW drivers as well.  (I know I have controlled them with LabVIEW interfaces.)

[svijay]

Thank u johnsold 

can u elaborate little bit more, because u said less than 150Hz..Now u r telling 75Hz .. I accept 75<150 but, why this much smaller value 

the clock inside the labview is in mS that means why can't we gernerate  1000 HZ...

If I understood something wrong ..Please  help me to know correct things

[johnsold]

To create a pulse takes two writes to a digital line, one high and one low.  Hence 150/2 = 75.

You can certainly set up a loop with a 1 ms delay.  However, the specifications on the USB-6008 indicate that the digital ports and the analog outputs are software timed.  The maximum update rate for AO is 150 Hz.  The digital update rate is not specified, but is probably similar.  The delays are probably in the way it communicates with the USB, one update at a time.

Lynn

[svijay]

Thank u for  ur immediate reply..

I gonna use bipolar stepper motor that means I will get 150/4 pulses per second 

am I correct?
But I need only 5 Rpm that is more than enough for my project

it is actually controlling the gun with two stepper motor..

If I use two stepper motor simultaneously whether that will reduce further speed reduction?

Is there any driver gives  more frequency..