"Bumps" in V-wheel motion

Topics Related to the ORD Bot Printer

"Bumps" in V-wheel motion

Postby orcinus » Tue Jun 25, 2013 1:54 pm

I've recently tightened my X and Y axes V-wheels quite a bit against the rails (i'm, sure someone will jump in and say "don't do that", but i have a good reason - the increased friction dampens the high frequency oscillations in the drivetrain and reduces the ripple by A LOT) and noticed something peculiar...

When tightened sufficiently, the axes exhibit rather noticeable "bumps" in the V-wheel motion. As if there were detents at points into which the wheel "falls in". They're perfectly periodic with the period of one wheel rotation, so i'm 99.9% sure it's an artifact in the V-wheel construction, but i can't identify it visually. There is no visible damage, dents or cracks. Also, it doesn't appear to be limited to a single V-wheel either.

Any ideas what might be the cause, Bart (or anyone)?
The only thing i can think of is that the V-wheels are slightly eccentric.
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Re: "Bumps" in V-wheel motion

Postby JakeS » Tue Jun 25, 2013 2:47 pm

I have seen and felt this in my laser; a small oscillation as the carriage moves with a wavelength that is about the circumference of the V-wheel. My completely unsubstantiated hypothesis was that the Delrin V-wheels are pretty stiff but still able to be squished when clamped down; when the carriage moves at a rate that is faster than the squished V-wheels' ability to relax, the 'squish' stays in one place on the wheel and the flat part of the wheel rolls around.
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Re: "Bumps" in V-wheel motion

Postby incognico » Tue Jun 25, 2013 3:20 pm

Yep, I have noticed that too. If you leave the wheel(s) with the "dent" rotated away from the rail for a while (like overnight), then the old "dent" is gone, and there's a new one formed at the rail contact point. I took this behavior as a sign the wheels were adjusted too tight, which I guess in hindsight is pretty obvious :)

Always interesting to read that others have had similar experiences.

--Nick
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Re: "Bumps" in V-wheel motion

Postby bdring » Tue Jun 25, 2013 7:37 pm

The wheels will dent if over tightened. They do tend to heal. You should only tighten them until there is no play. I tighten until they will not slip when spun. They cause the carriage to move if spun.
Bart
"If you didn't build it, you will never own it."
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Re: "Bumps" in V-wheel motion

Postby orcinus » Wed Jun 26, 2013 12:06 am

Yeah, i know what the "proper" tightness should be.
I've had it like that for a year, but have recently discovered that tightening beyond that point "cures" the rippling ("shadows") on sharp surface features (it acts as a friction damper).

Speaking of which, i wonder how the SS (or aluminium) V wheels would behave, vibration/ripple wise.
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Re: "Bumps" in V-wheel motion

Postby REdington » Wed Jun 26, 2013 12:31 am

I wouldn't use anything metal for wheels on the alum. If you really want to try metal wheels, rebuild your printer or build another one with hardcoated openrail.

http://openbuildspartstore.com/openrail-hard-coat/

Rodney
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Re: "Bumps" in V-wheel motion

Postby fma » Wed Jun 26, 2013 7:04 am

Did anyone try some friction stuff instead of the V-wheels? I'm thinking of using custom Delrin-base V-slider, with adjustable pressure mecanism.
Frédéric
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Re: "Bumps" in V-wheel motion

Postby orcinus » Wed Jun 26, 2013 9:26 pm

Yeah, i didn't suggest metal on existing rails.
If i were to do it, i'd have the makerslide HA'd.
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Re: "Bumps" in V-wheel motion

Postby flickerfly » Wed Aug 07, 2013 6:19 pm

Just to add to the body of knowledge here.

My problem was that my gantry and the upright makerslide were too tight. This was unrelated to the tightening of the eccentric spacer.
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