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Author Topic: Stepper motor and control advice for a pick and place robot arm  (Read 1278 times)
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Hi all,

I'm building a pick and place robot arm and planning on preprogram the arm to move the objects since all the things are put in a pre-determined place. That's why I'm thinking about using some stepper motors since the steppers and can be controlled by an arduino. (I have the Mega 2560). But I don't know what kind of stepper I'll need and what kind of motor control board I should get. Advice please!

For my current robot, I used tethered control with sparkfun servo control board and three 3-wire VEX motors. I have a 11.1 Li-Po battery and would like a stepper with torque greater than 6.5 in-lbs (VEX motors).

I found a stepper that is rated 3.35A but I can't find a control board that can handle that much current. Link: http://goo.gl/IckEQ

Thank you all for your time and effort!

James
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Examples (from another thread):
Power supply: http://www.circuitspecialists.com/ps1-150w-28.html (24V, 5.5A, $42.88)
Controller: http://www.circuitspecialists.com/stepper-motor-controller-xcw220.html (0.4A, $29.50)
Motors: http://www.circuitspecialists.com/nema_23_stepping_motor_57bygh207.html (8 kg cm == 6.97 lbs in for $13.95)

Does it have to be battery powered? "Pick and place" generally means it's an automated manufacturing machine (such as for populating electronic circuit boards), and thus typically plugged in.
Also, driving half an amp or more per winding per motor from a LiPo battery sounds like it will deplete available power in a hurry...
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Examples (from another thread):
Power supply: http://www.circuitspecialists.com/ps1-150w-28.html (24V, 5.5A, $42.88)
Controller: http://www.circuitspecialists.com/stepper-motor-controller-xcw220.html (0.4A, $29.50)
Motors: http://www.circuitspecialists.com/nema_23_stepping_motor_57bygh207.html (8 kg cm == 6.97 lbs in for $13.95)

Does it have to be battery powered? "Pick and place" generally means it's an automated manufacturing machine (such as for populating electronic circuit boards), and thus typically plugged in.
Also, driving half an amp or more per winding per motor from a LiPo battery sounds like it will deplete available power in a hurry...

Thanks for your reply. I am only a high school student so I don't know much about this stuff but I am very interested. So what I'm building is like a robot arm that will grab stuff like PVC pipes, pencils, batteries and nails and put them into boxes(the position of all objects are known prior to the competition). The aren't that heavy I guess but since my arm is really long and heavy(built with VEX metal) I thought I should have motor with higher torque. Also, the competition is 3 minutes and the voltage limit is about 15V so it has to be powered by battery. The switch from VEX motor to stepper is that I want the arm to be full automated instead of radio controlled since there was a lot of human error involved.

So I guess I could decrease the arm weight and use less powerful motor that draws less current, would you give me some more advice based on these information? Thank you!
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For just a high school project, a servo based arm might be easier to get started with. Search on youtube for "servo arm" and similar for examples.
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For just a high school project, a servo based arm might be easier to get started with. Search on youtube for "servo arm" and similar for examples.

As I've stated I built a servo based arm already but I'm looking for more precision movement, that's why I'm trying to use some stepper instead of servo, to get rid of radio control completely to decrease human error as all objects location are known prior to the competition.
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If you can give an estimate of the speed the motors need to go (in degrees/second or rpm) that is useful - making steppers go fast can be an issue.
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If you can give an estimate of the speed the motors need to go (in degrees/second or rpm) that is useful - making steppers go fast can be an issue.

It doesn't have to go too fast, maybe around 30 degrees per second.
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3 minutes is fine on LiPo, if you're using fast-discharge cells. (High "C" values) Try putting some cooling on the batteries, too (a small fan, some metal fins, perhaps :-)

Also, you may want to add another cell in series , to go up to 14.8 V nominal. (This is assuming your 11.1 is built out of three 3.7V cells) The motors won't die from that (in fact, they may run better, if you have a constant current controller.)

So, the controller I linked will probably work fine, assuming holding current is <= 0.4A. There are bigger versions, too.

Given the requirements, I think this description can perform very well, assuming you get the mechanics and control right. Good luck! Sounds like fun!
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Quote
As I've stated I built a servo based arm already but I'm looking for more precision movement, that's why I'm trying to use some stepper instead of servo, to get rid of radio control completely to decrease human error as all objects location are known prior to the competition.

Search the forum for CNC, which is the realm you have now entered.
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