Tuesday, February 19, 2008


Difficulties With Coupling

Yes, I know, you have some e-mail about a pill that can fix that. I wish. The Y Motor Coupling disintegrated on my Darwin. Aha! I have a PLA spare! That lasted about 20 minutes (not even long enough to print a new spare) before it melted and deformed around the hole for the motor-side grub screw. Clearly, the polycaprolactone part isn't going to get a much better lifetime, 'cos it would just melt sooner. We can try going high-tech with adhesives, using stiff plastic tube and hose clamps, or just machining a part out of steel. I'm going for the hose clamps.

Vik :v)

Good luck

I've had similar problems. I simply bought a length of square bar stock and chopped off about an inch, then centre-drilled the smallest diameter drive shaft end-to-end and then redrilled the larger shaft diameter at using the small hole as a guide for half the length of the bar.

I then tapped for #10 headless Allen set screws on each end of the coupling. Then you slide your coupling over the end of each shaft, drive and receiving, and tighten the Allen screws.

The only problem with that is that it is a rigid coupling, so your alighnments have to be very good or your drive motor has to be sitting on little rubber pads (my trick)that will let it flex a tiny bit.

Best, I guess, is to buy spider jaw couplings with that rubber bumper between the halves to take up misalignments. Those things can cost, however, at least $3-5 and often $15-20 depending on the shaft sizes and torque transmission requirements.


I could never find those for the tiny 2 mm drive shaft of my stepper motor at any price, though, and it would take a good machine shop to make them. :-(
It would be nice if somebody with an infrared camera (e.g. your local fire department) could take a look at an operating Darwin to see what parts are heating up.
I'm a member of the local fire department - no IR camera on station. Titirangi have one in the district next door, but it's kinda hard to borrow as it is official - very useful - kit.

Maybe they'd like a RepRap demo...

Vik :v)
You can do the same job with an IR thermometer, it's just not as sexy. :-p
I happen to be doing another small project right now where you need an IR cam. What you van do is hack an (old/cheap) webcam by removing the IR filter and put in a light blocking filter (i.e. photo negative). See also http://www.hoagieshouse.com/IR/

Brilliant IR camera link there Joost! Thanks!
That hack is for near IR, though...things just short of incandescent, in other words.

I doubt anything in a Reprap will glow with a short enough wavelength to trip a Si photodiode.

Better that Vik brings his setup to the neighboring town's FD, where I'm guessing they have some sort of cryogenic early-1990s monstrosity that will see subtle shades of temperature.
You need to look a little closer at the link Joost gave us, Joel. Take a look at the foot seen through the IR webcam.


Check out the veins. That's saying that you're seeing things about 80-85 degrees which is pretty good.

Most people don't realise that even things with a relatively low temperature give you a black body response which has a tail at the short wave IR that a sensor in the 0.8-1.1 micron range can see. That's how hand-held IR thermometers are able to work. If their sensors were tuned to the main pulse of a, say, room temperature blackbody response you'd be talking about a sensor in the 12-16 micron range, which is a bit expensive and usually requires either a cooling sink or a heated enclosure and a chopper to work properly. :-)
Post a Comment

<< Home

This page is powered by Blogger. Isn't yours?

Subscribe to
Posts [Atom]