Saturday, November 14, 2009


Ponoko Darwin Progress

I started building my Ponoko Darwin about a year ago. Got everything put together in about two months. Needed to upgrade the PC connected to the reprap, took on a job working for a start-up, and had no free time whatsoever. I still need to have a reprap, so I got started working on it again. Found several problems:
1) I have a Reprap Mother Board v 1.0, which isn't documented. Had to buzz out the pins.
2) I'd failed to solder the motherboard's stepper connectors; just diagonal pins.
3) In spite of what the website says, the Reprap's opto end sensors are inverting. When empty, they emit +5v. When interrupted, they emit 0.45v. Had to invert the sense. Perhaps the Sanguino test firmware should say "ran into endstop" when that happens?
The tests are running now. The X and Y operate fairly smoothly. Z is a bodge. WAY too much friction, even though I used a dry teflon libricant. Fails to move even when I have the stepper driver cranked all the way up. Will only move if I help it along. I suspect the problem is in the ball chain's mating with the gears. Advice cheerfully accepted for alternatives.

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Without the chain on, see if any Z drive rods are stiff. If the spring is too highly compressed, that will cause excessive friction.

Also , if the bed is wedged in a bit tight, the Z drive rods tend to get splayed or slightly bent. You might find things slack off if you replace the M5 bolts holding the Z bracket to the bed with M3 bolts and big washers. Slackening the bolts holding the bed off and letting things settle sometimes helps.

Vik :v)

I was struggling to see enough detail on the photo. It looks a little to me like you have bearing/s on both ends of your z axis threaded lift bars.

If this is the case the constraints on the bed brackets that slide up and down the corner posts could possibly be over constraining the Z movement.

It might be worth removing them.

If I have it wrong from the photo I apologize in advance.
It's great actually seeing some pics of a Ponoko! Thanks for posting! :-)
I second Forest on that, too
I took the nut and spring out of the picture entirely, and that helped a lot on one, but another still has substantial friction. I think I'll have to do as AKA47 suggested and cut the z axis threaded rod shorter.
I am not sure that I was sugesting you cut down the threaded rods.

Only perhaps that if your threaded rods have bearings at both ends you don't need the tabs/lugs that constrain the bed brackets to the frame corner posts (The smooth rods).

I would also advise going over your alignment if it is a little out it can cause binding.

Hope this helps.

cheers aka47
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