Increaasing z-axis torque

Okay. This is essentially a follow up to (http://dev.forums.reprap.org/read.php?14,32654,32654#msg-32654). I've tinkered some more, the Z is still binding. As far as I can tell, the frame is still pretty close to square (although I do need to check it against a right angle.) Assuming the frame is still square, I'm now toying with the idea of designing a reducing set of gears, along with a mount system to move to stepper off axis while keeping the drive rod in the same position.

I think this'll work because the stepper seems to be putting out *juuuust* a touch too little torque -- sometimes it'll manage to move to stage up or down, sometimes it'll bind. I was thinking of initially trying something like a 5:1 reduction.

Has anyone played with this, or have any thoughts on the idea?

L

I loosened some of the screws that hold the bed in place so that the rods have a little freedom to move relative to each other. I kept all the screws on the corner with the motor tight as well as those on the opposite corner.

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Darwin clone, Gen 2 electronics, Arduino Duemilanove w/ AtMega328, 5D Firmware, Pinchwheel extruder
[www.codeerrors.com]

Yup, I've done that too, McCoyn. I've actually also removed the two nuts that hold the tie brackes in place as well, just leaving them down at the bottom of the studding assembly. And I've cleaned the tie brackets and corner pieces out with a drill bit. And I've removed the back lash springs. And I've cleaned and oiled the whole thing countless times. And I've loosened the timing belt as much as it can be loosened. And I've switched the Z axis to full stepping. The posts all turn very smooothly. Wobble is pretty minimal. The system still just has a tight point in half it's cycle.

Perhaps I should note that the one place where I've deviateed from the RepRap spec is in the pullies/belt I'm using -- I found very cheap plastic pullies locally with the correct hub and diameter, (and nifty optical encoder rings), that take a High Torque Drive belt. So those are what I've been using (along with the obvious HTD belt) on me Z axis. Is there any way that swap could possibly be causing the SNAFU?

If not, I think I'm going to be building meself a gear box.

Cheers,
L

Greasing the threaded rods (don't go crazy) can also make a big difference in the amount of torque needed. Not sure how you are linking the shaft to the rod but I use vinyl tubing with a hose clamp on the joint and it works well while still allowing for slight misalignment and wobble

How much current are you running the Z stepper on, and how fast are you trying to move it? The Z axis doesn't have to move too fast; I've got a Darwin that will do 3000 mm/min on the X and Y, but it doesn't like to go much above 150 mm/min on the Z, although I haven't optimized it yet. Since I only move the Z 0.3 mm at a time, it's not a big deal. I also shoot for about 1 A on the Z stepper, but since it's not on all the time (I have it disabled except when it's actually moving), you can take it up quite high without worrying about overheating.

Can you spin the Z axis by hand when the stepper is powered off? It should be tough, but doable. If so, maybe you've got a bad stepper?

Wade

Maybe your threads aren't very good. You can run a threading die over it to recut them. It'll take a lot of work if you do it by hand.

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Darwin clone, Gen 2 electronics, Arduino Duemilanove w/ AtMega328, 5D Firmware, Pinchwheel extruder
[www.codeerrors.com]

The rods all spin quite freely -- the only one that has any real friction on it is the drive shaft -- when the motor is off, there's a fair amount of tension in there, although it just feels like the standard tension of an un-powered stepper. I'll check the amperage the stepper card is putting out -- I'm using the older, non-surface mount cards.