Backlash Issues in the Y

Bearings/Motors/Belts/Gears/Etc.

Backlash Issues in the Y

Postby gavztheouch » Fri Apr 27, 2012 7:33 pm

Hi I am having some backlash issue in my y axis.

If lock my y-axis motor and rock the gantry I can move the move the motor very slightly back and forward. Should this be the case, or should the motor always lock and hold its position exactly. If it should be solid, is there a chance I have a bad motor or have I wired it wrong. It seems to work well aside from the slight movement.

Thanks

Gav
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Re: Backlash Issues in the Y

Postby TLHarrell » Fri Apr 27, 2012 10:17 pm

I would start out with the easier stuff first. Make sure the mechanical parts are all tight. Check the motor mount, any rod connectors or pulleys. Check belt tension. Check for any pulley or connector wobble.

Once that's all cleared, then start into the electronics. Check wiring is properly connected per the pinouts. I would remove the offending motor, lock the coils and try the shaft with a pair of locking pliers. Check for the shaft moving in or out of the motor, or twisting.

That should at least get you started.
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Re: Backlash Issues in the Y

Postby gavztheouch » Sat Apr 28, 2012 10:23 am

Thanks for your suggestions,

I have checked all my mech linkages and I reckon I have about 0.1mm of backlash in them out of a total backlash of 0.5mm. I think the remaining 0.4mm is in the motor. My question would be, should the motor be rock solid? Bearing in mind I am not putting a huge amount of force on it to make it move.
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Re: Backlash Issues in the Y

Postby Techgraphix » Sat Apr 28, 2012 6:00 pm

You should not be able to move the motor (when it's powered).. only with brute force..
Even your 0,1mm backlash is much, imho.
The free-play should be around 0,00000 degrees..
What kind of coupling you use between motor and the rest? (photo or url.)
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Re: Backlash Issues in the Y

Postby gavztheouch » Mon May 14, 2012 12:54 pm

Image

Here are some possible issues I have found but can't quantify easily how much of an effect each on is having on the system. The biggest one for me is the deflection in the pulleys due to how I have mounted them on the MDT board and not something more substantial. I think it may also be worth my while changing the ball bearings in the hiwin linear guides to a free flowing set as this extra drag may be causing belt stretch? Finally the motor mount which I think is fairly sound as it is at least partially mounted onto the frame but it is still slightly moveable by hand.
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Re: Backlash Issues in the Y

Postby TLHarrell » Mon May 14, 2012 7:00 pm

I have heard of people disassembling and degreasing the linear guides to reduce friction.
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