more flexible timing belt

I could have sworn I saw a few projects that were using some kind of timing belt that looked like a spiral around a wire so that it could bend in any direction, not just in two dimensions. Now I can't find anything like that. Does a spiral timing belt sound familiar to anyone?

[www.sdp-si.com]

It's not anti-backlash like GT2 so you don't see many people use it.

Edited 1 time(s). Last edit at 11/30/2013 05:17PM by crispy1.

Thanks for the brand name and link crispy1! I originally tried searching for "synchromesh" but nothing showed up on Google so I thought I had remembered the name wrong.

This thread indicates that it has worked well for the Bukobot
[groups.google.com]
[deezmaker.com]

Seems to be working here too
[www.thingiverse.com]
[www.thingiverse.com]

Anywho, the reason I thought about this timing cable is that I want to see if I can move all of the motors to a stationary position, without using a bowden cable. A direct-drive extruder doesn't suffer from hysteresis, but normally it does require slinging a heavy motor around. A design like this [www.thingiverse.com] could relocate the motor so that you can control a direct drive extruder remotely. However, it does mean the timing belts have to move through some pretty complex paths, which include bends in more than one plane. I guess in theory you could bend a flat timing belt around with, like, idlers set at 45 degrees or something, but they're definitely not designed for that kind of motion. This stuff should be able to bend in any direction.

@ makeme

Review the pitch tolerance, it's quite large.
But that doesn't preclude it from working to some level of acceptance.

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This thread indicates that it has worked well for the Bukobot

Plenty of people got good results using T5 belts, too. Doesn't mean it's a good idea.

The posi-drive system should also be more flexible.. but I also think that gt2 is generally the best timing belt technology for 3d printing.

Edited 1 time(s). Last edit at 11/30/2013 10:10PM by iquizzle.

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iquizzle
I also think that gt2 is generally the best timing belt technology for 3d printing.

The point is finding a linear motion transmission system that can work in more than one plane. Belts are great if the axis of all of the bends are parallel, but if they're not, then it doesn't matter how great the belt is because it can't go where it needs to go.

After looking at the synchromesh it turns out they don't have an endless loop option, so that won't work. Maybe beaded chain or braided fishing line.

You actually can drive timing belts around corners. They easily twist 90 degrees to go off in a different direction, then twist back 90 degrees. So they can bend 180 degrees around an intermediate set of pulleys.

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iquizzle
but I also think that gt2 is generally the best timing belt technology for 3d printing.

I disagree loudly. For high loads and high tensions GT2 is a bit better indeed (and even there, i would argue in case of long belts). But at the loads and tensions we are running our repraps, that will never be a problem, and the high sensibility of the GT2 to grime deposits make it in my opinion a not so wise choice.

T2.5 has as good backlash behaviour as GT2, is mostly shrugging grime and its reinforced backside will keep tensions more even if env temps and especially humidity vary.
T2.5 also costs about nothing when compared to GT2. Gates marketed very heavily the GT2 but there is a lot of BS in their arguments

You only have to use good pulleys (even printed one will work if they fit profile), and from what I saw many of those from china are not very good. The best bet is to buy from an industrial components company near you and you'll get correct types, if perhaps a bit costlier.

T5 or T10 are unsuitable because of the minimum bend values. XL, HDT and others are simply obsolete

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makeme

The point is finding a linear motion transmission system that can work in more than one plane. Belts are great if the axis of all of the bends are parallel, but if they're not, then it doesn't matter how great the belt is because it can't go where it needs to go.

After looking at the synchromesh it turns out they don't have an endless loop option, so that won't work. Maybe beaded chain or braided fishing line.

You should still look at the posi-drive belts. They are also available on sdp-si. I've handled them and the seem quite flexible.

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alj_rprp
T2.5 has as good backlash behaviour as GT2, is mostly shrugging grime and its reinforced backside will keep tensions more even if env temps and especially humidity vary.
T2.5 also costs about nothing when compared to GT2. Gates marketed very heavily the GT2 but there is a lot of BS in their arguments

I really haven't encountered any grime in my belts even after 2 years of printing, but it's an interesting point and I'll think about that in choosing belts for my shapeoko. Really, I've been quite happy with GT2 and compared to MXL and HTD, they are significantly less prone to slipping. Considering that all of these belts/pulleys are pretty much the same price, I don't think it's worth buying MXL or HTD. My statement that GT2 is generally the best belt is based that they are rated for a smaller radius of curvature compared to T2.5, making them more useable in a larger variety of environments. There is also a much larger selection of pulleys available.

Edited 1 time(s). Last edit at 12/01/2013 10:51PM by iquizzle.

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garyhlucas
You actually can drive timing belts around corners. They easily twist 90 degrees to go off in a different direction, then twist back 90 degrees. So they can bend 180 degrees around an intermediate set of pulleys.

I'm not sure from reading that if you mean that they can be bent into new planes, or if you mean they can do complicated things in one plane.

I've attached an example of the sort of plane change I'm thinking about. Something like synchromesh or ball chain would seem to be sort of omni-directional in that it doesn't care what direction it's bent, but timing belts would be bi-directional in that they only bend back and forth. Do you mean that a timing belt can twist along its own axis so that it can bend in a new plane without prematurely wearing out or losing steps? If so, how much space needs to be reserved for the twist? A couple inches?

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iquizzle
I really haven't encountered any grime in my belts even after 2 years of printing, but it's an interesting point and I'll think about that in choosing belts for my shapeoko. Really, I've been quite happy with GT2 and compared to MXL and HTD, they are significantly less prone to slipping. Considering that all of these belts/pulleys are pretty much the same price, I don't think it's worth buying MXL or HTD. My statement that GT2 is generally the best belt is based that they are rated for a smaller radius of curvature compared to T2.5, making them more useable in a larger variety of environments. There is also a much larger selection of pulleys available.

Grime is only a big problem when there is some oil involved which is not really a problem in reprap but is one in milling.

The tensile cords and main materials are really where the 2 types differ a lot. GT2 is neoprene and small dia fiberglass cords, T5&T10 urethane and steel while T2.5 is urethane and either fiberglass or steel cords.

Neoprene make a lot of sense for a power belt (which what is GT2, not timing) as it tend to grip on pulleys, but it is not dimensionally as stable as urethane and the weaker reinforcements are fragile in case of convoluted paths. Large short belts in GT2 are very good.

ideal would be to use AT3 (improved T belt for high speed accuracy) in my sense, but it is quite a rare standard making it costlier for very small improvements. T2.5 is ubiquitous in Europe and easy to find everywhere and fit the bill easily.

alj_rprp

Good explanation!

You're not talking about this stuff?

[precisionparts.wmberg.com]

I have it on my repstrap. It's pretty good stuff.

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ShadowRam
You're not talking about this stuff?

[precisionparts.wmberg.com]

I have it on my repstrap. It's pretty good stuff.

Yea that's the stuff I mentioned earlier. The brand name it's usually sold under is called "posi-drive".

Thanks guys, that posi-drive stuff is described as handling non-parallel shafts and can be endless. I can't find much information on it outside of that. Time to experiment!

Try the belts and pulleys used by model helicopters for tail drive. Plenty of online sources.

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makeme

I could have sworn I saw a few projects that were using some kind of timing belt that looked like a spiral around a wire so that it could bend in any direction, not just in two dimensions. Now I can't find anything like that. Does a spiral timing belt sound familiar to anyone?

Might have been The Remoter thread in the Mechanics forum.