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Control dc motor using analog output from DAQ 6008

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Hi,

 

Since the 6008 DAQ does not output good quality PWM, can I control DC motor speed by using the analog outputs, protected by amplifiers?

Will this damage my DAQ?
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If your amplifiers are suitably specified, you should be able to do that.

 

Grounding, fault conditions, start up currents, .. are other things which should be considered in the overall design.

 

What are the voltage and current requirements for your motor? What else will your program be doing in addition to controlling the motor?

 

Lynn

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This is senior project we are working on:

 

The VI will capture depth information from the Micrsoft Kinect camera, and accordingly we will control the position of a car (controlled by 2 differential DC motors).

 

The position of the right hand is translated into X Y and Z coordinates in labview. We will then use the DAQ to control the speed and the direction of the motors.

 

The Car will be about 0.5 KG in weight, it will carry: 

 

1 small netbook + 1 router + DAQ 6008 + battery

 

We have not yet decided about the motors we are going to buy but they must do the job of carrying the above items.

 

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Solution
Accepted by topic author georges562

OK.  The motors will be rather small.

 

Consider using an LM317 as the "amplifier." Add a couple of protective diodes. Connect the AO to the Adjust terminal of the regulator with a resistor to ground.  Your output voltage can go down to 1.25 V and up to about min(Vbattery-2 V, Vaomax -1.25 V). If you have a 12 V battery and a 12 V motor, the maximum motor speed will be slightly less than the full rated speed. At the minimum voltage the motor will probably not run.  The regulator has built in protection against overcurrent and overtemperature.  This is about the cheapest motor controller you can make and actually works quite well.

 

If you need to reverse the motors, it gets slightly more complicated.  You can use a DPDT relay or an H-bridge of transistors.

 

Lynn

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Hi johnsold, I actually have the same problem. But probaly I didn't understand your solution to 100 % 😉


@johnsold wrote:

Your output voltage can go down to 1.25 V and up to about min(Vbattery-2 V, Vaomax -1.25 V). If you have a 12 V battery and a 12 V motor, the maximum motor speed will be slightly less than the full rated speed.


As I understood, the output voltage of the LM317 is limited by:

-Lm317_input_voltage minus round about 2 V

- V_AO_max - 1.25 V

That means a 12 V motor with LM317 connected to a 12 V batterie is limited at the one hand to 10 volt but at the other hand to USB 6008 AO max of 5 V -1.25 V = 3,75 V (?)

How can the maximum motor speed just slightly less than full rated speed ? Where is my mistake?

Thx in advance for your help

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Sorry.

 

I was thinking of other DAQ devices which have a maximum AO voltage of 10 V. With the 5 V output of the USB-6008 this method is not very useful.

 

Lynn

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