Problems with my [ply-] wooden McWire's GM3/RM2 powered leadscrews

I just installed the X motor on my [wooden] McWire and started testing it, and I need some help with of the problems I'm having.

The 1/2" OD, 1/4" ID silicone tubing from McMaster has a snug fit on the motor shaft, but just slides over the 1/4" leadscrew. I took a zip tie (those plastic cable control things) and tightened it around the portion of the silicone tube with the leadscrew in it, and while I can still move the leadscrew laterally within it (with a bit of force), it transfers rotary motion easily (I'm not sure if this will work on the z-axis, but it probably will).

The motor I'm using is a GM3 with an RM2 in it, with a 12ppr encoder. I turned the motor on for a bit, and the platform moved for a bit, and the silicone tubing slowly came off of the motor shaft. I attached a zip tie to this connection as I did with the leadscrew-tubing interface, and tried again.

Now, the tubing doesn't slip off the motor, but the motor has problems turning the leadscrew. It turns it for a bit, then stalls. When I increase the voltage (PWM) to the motor, same thing (though on some increases it doesn't move at all).

So a few problems:
1) I think the reason it is stalling is that there is too much friction between the leadscrew and the captive nut. I think I can fix this by applying some lubricant. Any advice on which kind to use? Would WD-40 work?

2) The GM3 is supposed to have a clutch which allows the motor to slip past the geartrain when there is too much torque required, right? How can I be sure this is happening? I think it might not be happening because my SN754410NE get's really hot in much less than a minute. I think the RM2 is stalling, and the RM2 stall current is above the suggested maximum for the chip. Perhaps it is due to the fact that I'm using a PWM'ed 12VDC supply instead of an actual 6VDC supply?
Or is the heat just normal? Would a simple fan blowing down on it (at a 45

Some people I work with on EDM are using Shoe Goo to make firm connections between gearmotor drive shafts and lead screws.

[www.eclecticproducts.com]

They are reporting good results. I haven't tried it myself, but it might be worth a shot.

I ran some tests this morning and basically:
1) The RM2 has it's pinion gear attached in a different way than the RM3. I don't think this is a problem, but just to be sure, I took it off and reversed it. It's a simple matter of pulling it off and putting it on the other way (after doing so, it looks just like the RM3's shaft).

2) The RM2, when mounted in the GM3 and powered by the DC Motor Driver v1.1, heats up the motor driver chip considerably (I used SN754410NE instead of L293DNE, but that shouldn't matter). I think it was overheating after a few seconds, reducing the supplied voltage to the motor, and causing the stalling.
I haven't tried the RM2 alone (i.e. not mounted in the GM3), but I suspect similar overheating would occur.

3) When I replaced the X-axis RM2 with an RM3, the chip remained cool to touch and the stage moved with decent speed (at least compared to the speed when it was using the RM2). I think I'll be using these RM3's from now on, as it seems that the driver board just can't handle the RM2's. If the RM3s burn out for whatever reason, I'll probably order some of those 12V motors people talk about (or maybe before then, as I imagine they get twice the max RPM; is this correct? I limit my motors to 127/255 Arduino PWM with a 12V power source on the driver board).

4) During prolonged testing (about 3-4 inches movement on the X-axis; it's more than I got before ), the silicone tubing eased itself off the GM3 output shaft. I suspect this is due to the fact that only a tiny part of the output shaft makes it through the support (that is, the shaft is only a little bit longer than the support is thick, and it goes through the thickness of the support, so only a little bit sticks out). The silicone tubing goes over the entirety of the shaft, as the hole is big enough for that, but the zip-tie that tightens the tubing onto the shaft is too big for the hole, so it has to sit outside on the small part of the shaft-tubing interface, giving it a crappy grip, which makes the tubing fall off after a short while.

To make a long story short (too late), I need a new coupling.

Forrest Higgs Wrote:
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> Some people I work with on EDM are using Shoe Goo
> to make firm connections between gearmotor drive
> shafts and lead screws.
>
> [www.eclecticproducts.com]
>
> They are reporting good results. I haven't tried
> it myself, but it might be worth a shot.

The product is interesting, and, while I'm almost sure it would work, I don't really want to glue anything to my GM3 motor shaft, as this is just a temporary RepStrap (and I imagine that once I get it running I can RP a plastic coupling that can fit over the shaft and fit into the tubing, or whatever else I come up with).

Are there any less permanent ways to attach the shaft to the leadscrew? I think if I was going to use glue, simple hot glue would work (and since it's a thermoplastic, it's kinda in the spirit of the project). Are there any glues that I can remove from the GM3's shaft when I decide to change the coupling?

Perhaps some sort of non-permanent or semi-permanent attachment to the shaft, which has on one side a hole in the shape of the shaft and on the other side a cylindrical portion which is shoved into the tubing and is long enough to get a firm tightening with the zip tie. Any ideas? Perhaps I should create a mold around the shaft and a portion of the tubing and cast this piece, if it would work and there is no better way.



Also, the zip ties have the little tightening bit sticking out. That is, when you tighten a zip tie, you push one end through a squarish hole in the other end, and this squarish hole, when tightened on a cylinder, forms a sort of bump on that cylnder (sticking out).
When I tighten the zip tie around the part of the tubing which contains the leadscrew (and cut off the extra portion of the tie), I find that the squarish thing that is buldging out comes dangerously close to the bottom of the X-stage. I can't actually tell if it will hit it (as I haven't been able to keep it connected to the motor shaft for long enough), but if it does, it will kinda smack the stage once per revolution, which may or may not be an actual problem.

Are there any good alternatives to the zip ties for tightening that don't increase the diameter of the tightened part by too much?



Give yourself a cookie if you read all (or any) of that.

I was going to try zip ties too, but realized before I put it on that the bulge wouldn't fit. I twisted a bit of bailing wire around it and then clipped of the twisted bit. Hasn't come off yet, and it's plenty small enough. If I was posting from home I could even post a picture of it.

I don't know what sort of wire it really is, I got a small coil of it from the trunk of a car a I bought from the junkyard. It was a good car for awhile too. I mourn its passing.

---

--
I'm building it with Baling Wire

jgilmore Wrote:
-------------------------------------------------------
> I was going to try zip ties too, but realized
> before I put it on that the bulge wouldn't fit. I
> twisted a bit of bailing wire around it and then
> clipped of the twisted bit. Hasn't come off yet,
> and it's plenty small enough. If I was posting
> from home I could even post a picture of it.
>
> I don't know what sort of wire it really is, I got
> a small coil of it from the trunk of a car a I
> bought from the junkyard. It was a good car for
> awhile too. I mourn its passing.


Interesting. A few more tests show that the zip ties are unreliable and the silicone tubing sometimes slips over the leadscrews while rotating (particularly noticable on my Y-axis where the shaft isn't precisely lined up with the leadscrew).

So, does anyone know a good place to buy bailing wire (I've found some options through google, but I'd appreciate input anyway)?

... in my motor-shaft-couplings i use pneumatic hoses, which are good stiff but a bit elastic too, so i could heat and wind/push them over the thread and motor-axis and use without any zip or such.

Look here at the images in my first post: [forums.reprap.org]

So it would be best to super-glue an adapter on the motoraxis, so it would heave the same diameter as the leadscrew and you can use a similar hose with the right diameter too ...

Viktor

Interesting Viktor, thanks for the advice. Looking at your pictures gave me an idea: perhaps I could wrap the leadscrew/motor shaft with some material (perhaps electrical tape, which was used for the captive nuts [as suggested in the documentation], or something similar) to increase the diameter of the shaft and leadscrew so that they fit more snugly in the hose/tubing, instead of using an adapter to change the motor shaft diameter or using zip-ties/etc to reduce the diameter of the hosing/tubing.
I'm going to attempt this first (as it would be quicker/cheaper in my situation than buying new tubing), and if it doesn't work I'll go with your method.

I'll try it in a few days (for various reasons, I can't do it immediately) and post my results.