Thursday, September 28, 2006


A bit further...

I got a 2x4 foot piece of 3/4-in fibreboard from Orchard today and sawed it down to 2x3 to fit on my work table and serve as a base for Tommelise.

I also shortened down the span of the z-axis to 650 mm as you see here.

I bought a coping saw, which you can see in the photo, so that I can cut some small pieces to make mounts for the shaft encoders for the GM8.

Just as a test I slapped the current edition of Wired magazine (~425 grammes) onto the coupling nut to see if the GM8 would have any trouble moving it around. You can see a short video clip of the GM8 not having any trouble.

About the only obstacle to progress is straightening out the threaded rod to limit lateral movement that you can see happening in the clip.

I decide to take things a step further before turning in for the night and strapped the 6v GM3 motor onto the rig since it was already equipped with a shaft encoder and controller board.

Duct tape is a wonderful prototyping tool. :-)

The pseudostepper control regime for the GM3 gearmotor worked fine. Here is a small video clip of the running at 0.484 seconds/step with a 12 degree step size. With this thread pitch that works out to just over 0.03 mm/step.

I'm currently running it at 4 seconds/step and 22.5 degree step size. That works out to 0.06 mm/step.

Are you using a short coupling or a ~1" one?

I'm seeing lots of resistance and I think it might be partly due to having a bigger coupling nut.
I'm using a 1" coupling. Sounds like you bought a tight coupling nut. From my own experience you'll find that the resistance decreases the more you run the coupling nut up and down the threaded rod. The off-spec bits get worn off.

Mind, this one that I just bought for Tommelise is very smooth.
This looks great, Forrest. I wish I had a little more time and experience to play as much with this stuff as you do. Maybe over the course of the next few months. :)

I'm seeing lots of resistance and I think it might be partly due to having a bigger coupling nut.

Have you already tried graphite or other lubrication? Might be worth it, and even better, if you could try several types of lubrication (graphite, grease, WD-40, etc) on separate couplings and let us know which works better!

I'd suspect graphite to be the better choice long term, since it may be less prone to collect dust?
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Looks sharp! How's the coupling nut for backlash?
Not much there and you can account for it in the firmware.
I've never really clicked with Wired, I do like The Economist though.

Either way, nice to see version two, always better and quicker to build that version one. :)

Beagle, yeah, I wish I had more time to build to. I've had a tiny bit of time, (but I'm spending less on the net) so I've been doing some soldering. Just learning, made a couple of crude H-bridges. Next I'll try to use some salvaged motor driver ICs.

Also got a hold of a massive LaserWriter Pro. Must be some good parts in there. :)

BTW, I've tried spray on graphite, might be a good match for threaded rods that have been worn down a bit. It dries and forms a thin paint like surface. Odd.

Okay, now must go mix epoxy...
I used to subscribe to the Economist. Gave it up a few years back. These days the only hard copy mag I subscribe to is Wired. The rest I read off of the web.
Beagle, I should have mentioned, WD-40 might not be such a good candidate, it evaporates very quickly. Good marketing though. ;) Maybe a good light machine oil, like used for sewing machines. Well, the old metal ones anyways!

Forrest, your copy of Wired has jogged my memmory, good interviews in there! Must look into it then.

Funny, I've moved away from the internet news a bit, and fill the gap on and off with local library copies of The Economist. More concise, less distractions!
I typicaly read the Economist free, online articles. Sadly, I haven't been to the library in years. There's really nothing worthwhile there any more. :-(
plaas: How do you account for backlash in the firmware? I didn't think it was that predictable...
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