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Motor Control

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windell747

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I'm wanting to purchase a stepper motor controller that will idenpendantly control either one or two (independently) 12 volt unipolar stepper motor with a 3A phase current.

I would like to feed ascii characters to this motor controller via a Linux PC RS232 com port commanding it to rotate the steppers. I would also like the controller to monitor the the feeback of an optical encoder and stop the steppers when the encoder has reached a certain position. Although, I would prefer the controller to monitor the encoder, I could also have the PC monitor the encoders position and have it command the controller to stop the motors. After the controller has finished rotating the motors, I would like the controller to pass back a command telling the PC that it is done rotating the antenna.

I would also like the PC to be able to cut all power to the controller and both steppers with some type of computer controlled relay via the PC's RS232 port.

I will be using this system to characterize an antenna by rotating the antenna to different elevations and azmithal angles. I would use these steppers, encoder and controller to rotate an antenna between tests. After the antenna is rotated to a new position, an antenna test will be conducted by the PC. While the test is in session, I will power down the controller and motor using the computer controlled switch to prevent EMI. After the test is finished, the controller and stepper will be powered back up to rotate the antenna to a new position.

My goal of this system is to autonomously characterize an antenna by rotating the antenna to all the angles an elevations needed.

Do you have any suggestions as to such a controller that recieves ascii command from a PC's RS232 port and monitors the output of an optical encoder?
In addition, do you have any suggestions as to a computer controlled switch or relay?

mahalo
 
The obviously solution is to use a PIC (or other microcontroller), or even use the PC parallel port to control the steppers?.

However, your BIG problem is that steppers only give relative positioning (and that's only providing they don't 'slip'), which is why you need some type of encoder to tell you where it is.

How about using servo's? - these are cheaper than steppers, more powerful than steppers, and provide absolute positioning - as the 'encoder' is already inside the servo.
 
Re: reply

Roboticinfo said:
Nigel there are two types of servos which one are you talking about?

Generally radio control type servos, where the feedback is used to give absolute positioning - NOT the speed control type servo systems, where the feedback is used to keep the speed (and sometimes phase) constant - as used in VCR's.
 
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The most torqe you can get from a rc servo is about 10lbs
which is pretty strong but some steppers have more power then that but do tend to slip like you said.
Peope that use rc servos for robotics tend to use an extrenal encoder and do not rely on the potentiometer in the servos.

So why do you choose servos??????
 
Re: reply

Nigel Goodwin said:
Roboticinfo said:
Nigel there are two types of servos which one are you talking about?

Generally radio control type servos, where the feedback is used to give absolute positioning - NOT the speed control type servo systems, where the feedback is used to keep the speed (and sometimes phase) constant - as used in VCR's.

so thats why when i tell someone at a shop that i want a servo they ask me "for what set?". now i get it, they assume i want a servo that is used in VCRs.

i hope i get an RC servo in my city. ive searched alot but i havent found any RC servo.
 
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The hobby shop by my house is expensive for servos but the robot shop by my house is the average price.
 
Re: reply

Roboticinfo said:
Actualy servos can go up to 24lbs of torqe.

As with anything, it all depends how much you want to pay?. But cost for cost, radio control servos are many times more powerful than steppers, and give absolute positioning - which a stepper doesn't.
 
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Yeah that is like a $70.00 or $80.00 dollar servo.

I good servo for sumo competition

Guarnted to beat the living daylights out of them.

Unless they have fast geared motors, then you are doomed.
 
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