Ideas for the next Wally.

Re: Ideas for the next Wally.

Postby Nicholas Seward » Mon Apr 27, 2015 1:04 am

Exactly except you will probably want two static nuts on each side of the spooling region. One of the nuts doesn't need to be axially restrained. (Actually it shouldn't be to prevent binding.)

You also don't need both wings on your coupler if you want to simplify.

You can also add gears to this but it starts to get a little busy. The gear will need to bolt through a set of bearings to keep it aligned with the steppers pinion. The big gear can then run the sliding/expanding coupler.
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Re: Ideas for the next Wally.

Postby realthor » Mon Apr 27, 2015 1:23 am

Yes, one wing would work too, good suggestion. It was more of a mental exercise though, as it is too long for my design.

Nic, I regarding the pulley redirect, I hope you can understand from my sketch. I was wondering how would this affect the math if I would cross the redirect wires?

screenshot.170.png
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Re: Ideas for the next Wally.

Postby Nicholas Seward » Mon Apr 27, 2015 1:26 am

@realthor: There is no effect except for reversing the drive direction of a stepper.
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Re: Ideas for the next Wally.

Postby realthor » Tue Apr 28, 2015 2:50 pm

Wouldn't UHMWP be a suitable choice for pulleys or other parts maybe where the movement is minimal? I am thinking linear rod bushings to replace linear bearings and so on.

I am considering for my Z a winch system and a block and tackle approach to reduce the strain on the steppers due to the carriage weight and realized that the rotation of these pulleys is minimal.

Thanks.
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Re: Ideas for the next Wally.

Postby Nicholas Seward » Tue Apr 28, 2015 5:39 pm

It is a good material but it typically requires machining. Therefore, it isn't something you are going to print. Therefore, it will probably add to the costs. 20 ways to skin a cat. In the end, the cat is still skinned.
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Re: Ideas for the next Wally.

Postby realthor » Sun May 03, 2015 11:29 pm

I need a piece of advice regarding a type of gear that I think I've seen somewhere but can't remember anything more than that.
This is a screw-type threaded rod that also has a gear profile on its threads so that another gear can engage it to rotate and advance through the nut, something like this:

screenshot.183.png
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I am sure this does exist. Does it have a name? I am thinking about this as a way to spool without having to rely on sliding/extending couplers.
1)Would this be a printable design?
2) Would an extended coupler of the type i've previously shown be easier to print/create than this?


Thank you.
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Re: Ideas for the next Wally.

Postby Cozmicray » Mon May 04, 2015 12:43 am

It's a worm gear

Search on thinkaverse

http://www.thingiverse.com/thing:18544
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Re: Ideas for the next Wally.

Postby realthor » Mon May 04, 2015 9:14 am

@Cozmicray: i have briefly studied the wormgears when I was thinking of a solution for my idea but I now realize I was a bit unclear in my question (happens a lot when you lack the technical terminology):

1) worm gears seem to always have a sort of caved profile with angled teeth for the non-engaging gear (for best possible contact I suppose) and I was not sure that the profile of the non-engaging gear can simply be a straight involuted gear.
The profile I mostly see on the web is like this:

Image

2) My question was actually more about the engaged gear/screw, as it needs to both be engaged in axial rotation (solved by a worm gear too) and translation through a nut (this is going to be a side effect of the rotation if a screw-type thread is also embedded in the design of the profile), hence it has to both have a straight involuted profile and a screw-type thread at the same time.

Searching deeper on the web I have found the electric worm gear screw jack to be something very similar to what I was thinking, I just need the screw to actually rotate to spool the spectra line.
I hope the sketch below can transmit something:

screenshot.185.png
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Re: Ideas for the next Wally.

Postby realthor » Mon May 04, 2015 9:13 pm

One pretty rudimentary solution would be a spur gear of some length (3d printed), fixed to a normal bolt.
A wormgear would engage and rotate the spur gear while the bolt, rotating, would also advance through the nuts, spooling the line at the other end.

screenshot.190.png
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I try to use a normal bolt for the benefit of the strength and availability. I don't think 3d printed bolts will replace metal anytime soon.

For the "spur gear cylinder" 3d printing seems to be the only solution (cost/availability for metal/brass spur gear stock would make this a unfeasible solution).
Because the contact surfaces between the wormgear and the spur gear can't be optimized for maximum contact (the engaged gear/bolt assembly must be allowed to slide), the plastic might be too weak to take the forces involved (even with MA). This is something I can't give an educated guess for, maybe you can tell from experience.
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Re: Ideas for the next Wally.

Postby Nicholas Seward » Mon May 04, 2015 10:45 pm

The forces will be pretty small and it would be easy for plastic components to work for this. I like the worm/spur idea better than the spur/spur idea. The reduction of the worm would actually allow you to get away with a huge screw that could be printed easily.
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