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Post by Dingo on Jul 13, 2004 23:30:55 GMT 10
What would be the best way to create a home-build robotic arm with a wrist, elbow and shoulder?
I assume a long threaded screw attached to a dc motor that was controlled by a Microcontroller would be the best way of accurate control each joint.
Would it be sufficient to encase this all in PVC or would it be best to have a flexible exterior?
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Post by ZapBrannigan on Jul 14, 2004 16:46:01 GMT 10
In particular, the dc motor ought to be a stepper motor for accuracy (assuming no slippage), or you would need to have sensors.
Also depends on how much power and strength in maintaining position you want. Pneumatic muscles keep their strength but are much more expensive and cumbersome. In a dc motor arrangement, you could be straining the gears and or needing the motor to apply forward pressure to hold the arm in place...
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Post by Bones on Jul 16, 2004 11:56:55 GMT 10
If it's a robot pincer type arm there are slow 60RPM motors that jacar sell for turning the arm. Thats what I'm using for rotation. But servos are proportional so you can tell it to go there and it will. But as Zap said the motor will constantly be on to keep that position. The other way is the same as a servo but gear it down and put a higher rev motor in it. If the gearing is a really low geared (high ratio) it is very hard for it to make the motor spin. And use the high rev motor to make it work a lot faster.
Bones
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Post by Dingo on Jul 16, 2004 14:24:00 GMT 10
Yep - all very interesting.
I was thinking that you could have a nut and bolt (a really long bolt running the length of each segment) arrangment.
the nut would be fix to the arm and then have the dc motor would spin the bolt. That way once the motor stopped the nut and bolt configuration shouldn't slip (well not too mcuh anyway). That way you'd save your power and motors.
You could even have a brake grasp the threaded bolt (a gripper of some sort)once the motor stopped and since you would have just immobilised the bolt and the nut is fixed anyway, you'd stop any slippage.
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Post by Bones on Jul 16, 2004 19:46:07 GMT 10
I was looking at the same idea. But having the motor built around the thread and hooked onto the nut through a planetary gear system to reduce it. You would need some kind of varible resistor like a 10 turn pot to know the position. Just like a servo. and then I looked at the $15 servo sitting next to the design and went mmmmm cheaper.
I'm still looking at that design and the do have and item like that whick has roller bearings in it for a dfferent purpose. No motor attached. But expensive.
It would have to be greased up to stop wear.
Even a rack and pinion idea would work.
I'll be looking at making one soon to test.
I'll give you a yell.
Bones
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