Ideas for the next Wally.

[realthor]

We're still talking metal bolt as a base right?

[Nicholas Seward]

@realthor: No you could easily print the bolt and the nuts. I would use a nominal diameter of 16mm or bigger. This could be an easy 3 part assembly.

1) Two integrated nuts and stepper mount
2) Worm gear
3) Spur gear/ screw thing

You just size the components so that they are strong enough.

[Cozmicray]

I suppose it would be good to know what this
mechanism has to do?
Then a gear or mechanism to accomplish that can be suggested.
Even a outlandish complicated mechanism that you like?

Now that I look at your drawing
it is a screw with gear teeth cut axially around the circumference.

You could take a splined shaft and thread it
or
take a threaded rod and cut splines (gear teeth) in it.

But to what end?
Rotory to linear movement

I don't understand "a way to spool without having to rely on sliding/extending couplers"

Sounds like you are trying to combine too many functions together in one?

Threadless leadscrew with splines?

Perhaps a fishing reel to spool?
A casting / spinning reel

spinning_reel.jpg (29.1 KiB) Viewed 65030 times

Baffled?

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:

The attachment screenshot.183.png is no longer available

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.

[realthor]

I suppose it would be good to know what this
mechanism has to do?

We're talking a few pages now about a winch-style Z that will be spooling fishing line without triangulation.

This Z-axis assembly would be using fishing line instead of a leadscrew or any other complex/difficult to machine/not easily available part. This can be achieved in a CoreXZ style or a winch-style and I went with the winch system. But any whinching would introduce triangulation errors so I am exploring ways to avoid that. One option is an extending/expanding motor coupler (discussed before/images provided/etc), the other is the "threaded and toothed" rod actuated by a wormgear.

Even a outlandish complicated mechanism that you like?

It's actually the simplest i got so far. As Nic said, mostly 3d printed components. Even if it would be "outlandislly" complicated, if it can be 3d printed it's still in rep-rap teritory and the complication would be in the design. But it's not

Now that I look at your drawing

You could take a splined shaft and thread it
it is a screw with gear teeth cut axially around the circumference.
or
take a threaded rod and cut splines (gear teeth) in it.

Yes you got my initial idea right: a threaded rod with spur gear teeth axially cut in it. That single rod would have needed only a stepper with a wormgear and two fixed nuts to build the Z-winch. Where do you see a complicated design?

[realthor]

@realthor: No you could easily print the bolt and the nuts. I would use a nominal diameter of 16mm or bigger. This could be an easy 3 part assembly.

1) Two integrated nuts and stepper mount
2) Worm gear
3) Spur gear/ screw thing

You just size the components so that they are strong enough.

@Nic: do you think we could 3d print such a hybrid spur gear - screw thing? This would make the winch incredibly simple. This is how it would look when integrated with other supporting elements in my sketches:

screenshot.194.png (127.6 KiB) Viewed 65012 times

I have no clue about the math that would render a 3d model of this (I can imagine though threading a spur gear stock or cutting teeth in a threaded rod) but I am sure this is something an OpenScad or SolidWorks user can easily put together.

Would the strength of such a detailed print be an issue or do we rely on scaling it up until it is strong enough?

As an advantage, the motor placement and the proximity of the nuts to where the force is applied by the wormgear to the threaded spur stock allows quite a long rod. Moreover, the shear force caused by the spooling is very close to the nut so there is virtually no bending of the plastic rod. The nuts can even get closer to one another by turning the motor 90deg on the Z (pointing the shaft into the wall so to speak).

[Cozmicray]

Original Wally was a Z-lift using string?
A pulley on Z-table in a Class 2 or single movable pulley arrangement
with end being taken up by screw on stepper motor.
2 to 1 advantage helping to hoist the heavy rock table.

I found the string naturally followed the threads without the need
to guide it.

Why is it so critical to provide precise spooling

Combining the shaft rotation with shaft feed is over complicating this mechanism.
A threaded rod has to freely slide thru two bearings?
If it were a good design every winch and fishing reel would using it.

Perhaps a look at
http://en.wikipedia.org/wiki/Wire_rope_ ... technology

and other spooling technology (search "winch spooling device" )

I accept you are anti KISS
but what good does a un-makeable, un-useable, un-reliable design really do?
You could have built six Wally's in the time?

Sorry Nick ban me for Veritas!

[realthor]

Why is it so critical to provide precise spooling.
If it were a good design every winch and fishing reel would using it.

Winching doesn't suffer from triangulation, the end of the cable is so far away it doesn't really matter. The main concern in a winch is orderly arranged cable so that it doesn't damage due to the high loads and doesn't build a coil that stucks the whole mechanism. Also this design wouldn't work for the jobs winches are used for as they need very long cables that can't be accommodated in a single row. Not the same requirements here.

I accept you are anti KISS

I must have a different concept of KISS then. And then again, your opinion that I am anti-kiss is something you have decided. And then again, you might as well not accept it.

You could have built six Wally's in the time?

It is not my immediate goal to build a wally. Wally doesn't work as he is. I am sorry you are so frustrated that your wally doesn't print right. Not my fault, please don't take this on me, I don't want to fill this thread with non-constructive posts, be they as polite as they are.

I am quite happy to move my posts to a separate thread if that would make you happy.

[Nicholas Seward]

This could all be 3D printed easily. The design side is a little tricky but not too bad. I would like to prototype this if I can find the time but let me make a few notes for discussion purposes.

1)The nuts would be printed in the same part that holds the stepper.
2) The nuts can be designed to not get close to the root of the screw so that the string can actually wrap around the screw and go through the nut at the same time.
3)I would have the string leave the screw between the nuts.
4)The screw will have a large enough diameter (20ish mm) so the screw doesn't need travel very far axially. For most desktop printers you can get by with 3-4 rotations.

Now for a little math... I think the worm/spur ratio could easily be 16+:1. With a 20mm root diameter on the spool and a 45oz-in stepper you will 100+lbs of force and you will get a resolutions of about 20um per full step.

This setup is prone to backlash but gravity should take care of that. You can also make this a two sided design with the stepper turning a worm that interfaces with two screws. Tensioning the string in the system will remove the backlash.

[realthor]

This could all be 3D printed easily. The design side is a little tricky but not too bad. I would like to prototype this if I can find the time but let me make a few notes for discussion purposes.

1)The nuts would be printed in the same part that holds the stepper.
2) The nuts can be designed to not get close to the root of the screw so that the string can actually wrap around the screw and go through the nut at the same time.
3)I would have the string leave the screw between the nuts.
4)The screw will have a large enough diameter (20ish mm) so the screw doesn't need travel very far axially. For most desktop printers you can get by with 3-4 rotations.

Now for a little math... I think the worm/spur ratio could easily be 16+:1. With a 20mm root diameter on the spool and a 45oz-in stepper you will 100+lbs of force and you will get a resolutions of about 20um per full step.

I haven't calculated pretty much anything yet but I have also considered the pulley-based reduction so, cleared of almost everything to better see the Z stuff, my design looks right now like this (excuse the sloppy mechanical design skills):

screenshot.198.png (43.63 KiB) Viewed 64993 times

I have moved the string to the middle of the bot, between the nuts; I haven't considered it before because I wasn't sure how to go with the string through the nut . Experience talks in your suggestions.

This setup is prone to backlash but gravity should take care of that. You can also make this a two sided design with the stepper turning a worm that interfaces with two screws. Tensioning the string in the system will remove the backlash.

Do you mean having another 2-pulley anchor below the Z carriage? I can't immediately imagine this.

[Cozmicray]

So what is wrong with design

viewtopic.php?p=255#p255

Postby fabrice » Tue Dec 31, 2013 1:01 pm

with winch or leadscrew?

What are advantages with your design?



It's really NOT WALLY anymore
deserves a new name -- new forum section? Haskel, Beaver, Ward, June, Cleaver