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### Topic: Need opinions on servo motor control for heavy applications (Read 5753 times)previous topic - next topic

#### cmd1024

##### Nov 25, 2012, 12:19 pm
I want to control a servo motor using Arduino and sensors. But all the example schemes or tutorials so far I found are for motors used in toys, low power applications. My task is to control a servo motor which can drive higher torques and lifts up to 100 kg. My concerns:

1-) Is the schematics and circuitry same with the RC motor examples or one should use extra circuitry such as power amplifiers for big motors?
2-) How to choose the proper type of motor for my task?
3-) Is there any reference to learn more about Arduino control of motors used in industry or more powerful applications?

Thanks,

#### johnwasser

#1
##### Nov 25, 2012, 05:24 pm
For high-power position control you will probably have to implement your own feedback loop.  You need a motor capable of the torque and speed, drive electronics capable of providing the necessary power, and a way of measuring the current position.  The desired position is compared to the current position and a PID (Proportional Integral Differential) calculation will determine the speed and direction to drive the motor to reach the desired position.

How much torque do you need and how fast do you need it to move?  You can se a gera motor to get more torque at the expense of speed.  More torque and more speed will require more power and thus a bigger motor and heftier power controllers.
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#### cmd1024

#2
##### Nov 26, 2012, 06:51 pm
Hi thanks and sorry for the late response. Here is our task.

We are planning to adjust the level of a load (around 50 kg) by using an electrical motor. Now we are using a hand crank and we want to get rid of this manual process.

For example we want to implement a control where one can adjust the height of the load. The load is hanging down on a pulley. We want to keep the load at 4 different fixed heights by using an easy push button system or a computer. When one sends signal to the motor the motor will adjust the load to a particular height depending on the signal and then will stop there.

What type of motor and electronic control can be used?

#### johnwasser

#3
##### Nov 26, 2012, 11:11 pm
Does the hand crank drive a cable winch?  If so it shouldn't be too hard to replace that with an electrical winch.

With an electrical winch you could use a simple switch to count turns of the motor and a limit switch to indicate the "Full Up" position.  To get to the other three positions you can move up or down and count turns of the winch.  It won't give you millimeter precision but it won't cost a fortune, either.
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#### cmd1024

#4
##### Nov 29, 2012, 07:26 pmLast Edit: Nov 29, 2012, 07:33 pm by cmd1024 Reason: 1
hello John,

Sorry for answering late. Hope you are still interested. I decided to apply a 5V motor configuration for a 24V motor for more torque. I would like to have your opinion if it is doable or works? Here is my plan as follows:

Now I'm controlling a 5V motor with Arduino but need more torque which means a more powerful motor. Here is my scheme. (I took it form a tutorial):
http://img21.imageshack.us/img21/1731/stepperarduino.jpg
Here Arduino is controlling a 5V unipolar stepper motor through a Darlington transistor.

My question is if I just change this motor with a 24V one and feed the new motor with an external 24V power supply and remain the rest configuration same would the motor still be controlled? Or do I need another configuration?

I also asked this to another forum, I hope I can learn about it.

Thanks for sparing time!

#### johnwasser

#5
##### Nov 29, 2012, 08:24 pm
You would have to check that the ULN2803A can switch the voltage and current the bigger stepper requires.  To do that you would need to look at the datasheet: http://www.ti.com/lit/ds/symlink/uln2803a.pdf

Looks like 24V is not a problem (the datasheet says it can handle 50V).

The maximum current (500 mA) might be a problem, depending on the motor you are trying to drive.
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#### PaulS

#6
##### Nov 30, 2012, 12:19 am
Quote
The maximum current (500 mA) might be a problem, depending on the motor you are trying to drive.

I'd look for a driver that can handle at least three times the current that the motors typically need. Nothing like a little binding letting the magic smoke out to ruin your day.

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