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arm robot may have only 2 motors

Posted by xoid 
arm robot may have only 2 motors
April 13, 2012 08:09AM
Usually if you want 3d print you get 3 motors for X, Y, Z axis. In polar bot, it is the same. 3 motors mean a 3 drivers, pins of MC etc.

But I can offer 2 motors 3d printing by polar arm bot. This bot has no Z axis, only X and Y arms . 1 and 2 are treaded rods
To make Z movement (up or down) X or/and Y arms JUST DO ONE FULL TURN and thus move up or down at one thread step. The usual X-Y movement are processing with little angle so they are not influence the Z axis.
Also , threaded rods can have different steps, and full rotation X arm and Y arm in opposite direction can give another Z motion.

What do you think about my idea?

| |
| |============ EX
1 | | UD
| | | | ER
+--------------+========== -------| V
|----------------=============== PRINTED
|_________| PART IS
Re: arm robot may have only 2 motors
April 13, 2012 08:23AM
Not practical.

Using 8mm threaded rod that is 1.25mm per turn!
A difference of 0.1 mm can make the difference between a good and a failed print.

You would have to make it such that one motor is set to a max position that flips a lever that then allows the other motor to drive the z-axis. Then the first motor moves away to flip the switch back. This could be workable...

...but you proposal would mean that the height of the extruder over the bed would fluctuate as much 0.625 mm!!
And 0.1mm is already way too much varience.

You will never get a first layer to stick with this mechanism!

Bob Morrison
W├Ârth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse
Re: arm robot may have only 2 motors
April 16, 2012 06:04AM
A cartesian robot could be capable of 3D movement with two motors.

Old typewriters had a carruage return mechanism that could be used on a cartesian robot. XY motors would work as normal, but when you wanted to index in Z you could home to one end and hit a trigger to raise the Z axis (Other end could lower the axis)

What must be borne in mind is that motors are relatively cheap nowadays and the mechanical mechanisms are often the most expensive part. This is why a prusa uses two motors for the Z axis as it is cheaper.
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