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Deviant Behavior

Posted by degroof 
Deviant Behavior
March 14, 2008 05:24PM
As I've been (slowly) building my Darwin, I've deviated from the standard design in a number of places:

- used metal gears for X, Y and Z axes
- used metal couplings for Y and Z motors
- added a tensioner on the Z belt
- omitted the backlash springs

The first two were done mainly for the sake of durability. The other two were an attempt to get the Z belt to stop slipping.

Has anyone else done any interesting tweaks?
Re: Deviant Behavior
March 14, 2008 10:52PM
Yep I have done all of these. The big problem I have is trying to get a coupling that works on the motor to rod connection mine has a lot of movement..

Re: Deviant Behavior
March 14, 2008 11:51PM
Windshield washer tubing for your car. Got mine at Shucks. Costs about a buck or two a foot. You only need one foot. Works like a dream. Allows much deviation in your construction method--as pointed out by Forest--and won't bind up horribly if you chance to run your stages into things (#@$%!!!!). I have a time or twenty... ;-)

Re: Deviant Behavior
March 15, 2008 11:52AM
what is the inside diameter on that stuff, Demented?
Re: Deviant Behavior
March 15, 2008 03:49PM

.2" ID and .4" OD. Good elastic stuff for small deformations. Past a certain point it breaks down. Good stuff though

Re: Deviant Behavior
March 15, 2008 04:07PM
Damn! I need 0.08. sad smiley
Re: Deviant Behavior
March 16, 2008 08:07PM

You might take a peak in a fish store. Their air lines are sometimes really small. Not as elastic as the stuff I'm using but could work. Also, don't rule out a solid chunck of rubber. 80 thousandths is small enough that if you make a slit in it you can just put in a bit of rubber cement or some such and push the shaft in. Or, zip-ties work well for holding those things together too.

Re: Deviant Behavior
March 18, 2008 05:47PM
Have you considered shrinkwrap? I know the stuff gets brittle after you've deformed it, at least if you keep applying heat, and I don't know how much resistance to torsion it'd have, (probably not much,) but it might work for you.
Re: Deviant Behavior
March 19, 2008 12:36PM
Or that heat-shrink tubing stuff that we use for bundles of wires. comes in different sizes so you could layer up quite a hefty wall thickness on your joint. Just thought of it because of Sean's idea of shrink wrap. Essentially the same idea. Could apply both of these together if you needed greater wall thickness. Also, I don't think the tubing would be as brittle.

Re: Deviant Behavior
March 19, 2008 01:02PM
For flexible shaft couplings, compression springs work well. I'm not using any on my Darwin build but, on past projects, I've used a spring from a retractable pen as an improvised U-joint.
Re: Deviant Behavior
March 19, 2008 01:10PM
Another hack. I ditched the flexible shaft on the extruder, shortened the motor mount and added a filament guide (paperclip).

Re: Deviant Behavior
March 19, 2008 01:12PM
Nice filament guide idea. Elegant! smileys with beer
Re: Deviant Behavior
March 19, 2008 03:00PM
... i used pneumatic hoses for coupling, they are stiff enough but have some inherent elasticity, so you can push them over thicker rods or threads:

Here: [forums.reprap.org] we discussed some of the specs ...

Re: Deviant Behavior
March 20, 2008 10:51PM
Sorry, I misspoke
Shrinkwrap is like saran, only designed to shrink up under heat. It'd actually probably be lousy.
Shrink tubing is what I intended to say, but I work with shrinkwrap nearly every day. (Heat sealer at work.)

shrinkwrap won't just get brittle if you keep applying heat. It'll burn through.
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