Subject:
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12t crown bevel gear
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Newsgroups:
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lugnet.robotics
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Date:
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Fri, 31 Aug 2001 03:17:33 GMT
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Viewed:
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456 times
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I have designed a very small robot arm that has a shoulder that moves up and
down and a wrist that moves up/down with a pneumatic gripper at the tip. I
think this is called 2 DOF (degrees of freedom). The goal of this robot is
to pick up light objects (my son's wooden square alphabet blocks).
I am keeping both motors at the base of the robotic arm as opposed to
putting the motor that drives the wrist at the wrist joint. I just transfer
motor power (after gear reduction and worm gear) to the wrist joint by using
12t crown bevel gears at right angles with each other and an axle running
the length from the shoulder joint to the wrist joint.
The problem so far has been that as one uses more of these 12t bevel gears
at right angles, there is more and more "give" (axles turning without motor
turning) in the axles because the bevel gears do not fit perfectly together
or "mesh" together.
This makes it extremely difficult for determining an accurate position of
the wrist at any given time.
The second effect (and more difficult effect to explain) is the wrist tends
to "fall" a short distance when rotated about the wrist axis from upside
down position behind the shoulder to right-side-up position in front of the
shoulder (as in dumping object in basket behind shoulder to moving wrist in
front of shoulder ready for next object). This occurs just after the wrist
is pointed vertical in the air and begins to rotate down. Instead of a
smooth movement (because of motor movement) of back to front, the wrist
falls a short distance (not because of motor movement) and continues moving
smoothly with motor movement. This fall is severe enough to make the bevel
gears slip until the wrist hits the surface.
Any help with this would be appreciated.
Thanks,
Clayton
P.S. I thought about doing a little artwork, but my attempt might cause more
confusion!
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Message has 1 Reply:
 | | Re: 12t crown bevel gear
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| (...) This is often referred to as backlash. (...) I think your second effect is probably also due to backlash. Since the fall occurs just past the wrist's balance point, I infer that the gear lash is changing directions. Reducing it in the worm (...) (23 years ago, 31-Aug-01, to lugnet.robotics)
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