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Tripteron Implementation

Posted by Apsu 
Re: Tripteron Implementation
January 05, 2017 10:08AM
Quote
o_lampe
I just stumbled across an interesting bearing type called "cam follower cf5"

This might be a good solution for the z-axis dual rods?

Hrm. Interesting. Could be a few uses for similar parts, perhaps. I think the challenge is still what to mount any kind of bolt/axle in so it doesn't tilt or deform the mount, if the mount is plastic. It's tricky. An ideal situation would be to find an existing part that's commoditized and priced low, yet allows for metal-metal mating of a radial element.

I keep going back to strap hinges and looking for ones that are small enough and with a reasonable enough hole pattern they could be bolted to extrusions and form the joints. And made well enough they wouldn't have any play in them. I think that's the simplest all-metal commodity option that has the desired properties.
Re: Tripteron Implementation
January 05, 2017 11:11PM
On a similar note I came across these bearings that are rated for moments. But I actually think the two bearings clamped towards each other gives you a similar setup. thumbs up

It sure would be nice if there was a 15mm version of this. You could just throw in some slippery washers or thrust bearings and be done with it.

Edited 1 time(s). Last edit at 01/05/2017 11:12PM by brazenrain.
Re: Tripteron Implementation
January 06, 2017 08:15AM
Quote
brazenrain
It sure would be nice if there was a 15mm version of this. You could just throw in some slippery washers or thrust bearings and be done with it.

Yes indeed! I've looked a lot at the die-cast and similar extrusion pivots, but they're really expensive. Well... they were really expensive, before I got to the point of getting joints machined which definitely costs more tongue sticking out smiley I'm not sure if you could find any made for 1515 and 2020 is pretty bulky, but this is what I had my eye on previously. I also don't know what kind of lateral load stiffness they have, but it's probably pretty good since they're designed for framing moving portions of large assemblies.

I also ran across these but they're for larger profiles

[www.minitecframing.com]
[www.minitecframing.com]

But man are they rated for high lateral loads and appear to be rock-solid!
Re: Tripteron Implementation
January 06, 2017 11:49AM
Prototype machined joints came in!





Bolt holes are nice tight clearance fits, bearings fit great, tolerances and clearance are great, and the joint is, as expected, rock solid grinning smiley

I paid for these and asked the guy to make the other 10 for me, because for the rapid turnaround time and one-off nature this is perfect. Should have a machined assembly put together in a week or two looks like smiling smiley
Re: Tripteron Implementation
January 06, 2017 07:43PM
Nice joints, musta cost a packet, looking forward to seeing them in action.
Re: Tripteron Implementation
January 07, 2017 05:38AM
Quote
MechaBits
Nice joints, musta cost a packet, looking forward to seeing them in action.

Yeah, me too! They were reasonably priced considering. About $65 for the pair, he was asking, but I did pay the guy extra because he did great work and treated me great. Forging that relationship is worth it. And really, cost of prototyping... I knew what I was getting into grinning smiley Not going to be cheap, but I hope to A) have a kickass machine and cool smiley better inform the next design iteration. We'll find out!
Re: Tripteron Implementation
January 07, 2017 09:47AM
In the meantime I'm looking into these. How do you think delteron will hold up with 10mm arms?
Re: Tripteron Implementation
January 07, 2017 10:41AM
Quote
brazenrain
In the meantime I'm looking into these. How do you think delteron will hold up with 10mm arms?

Oo interesting. I mean, it really depends on frame scale. In the 300ish XY frame member scale, and thus 300+ arm length scale, it seems like 15mm links is just big enough.

However, if those hinges can be low enough friction without a lot of slop (getting the nut tightness just right from the look of it?)... you can make a parallel 10mm arm system pretty easily. Because I assume the hinges are cheap, and the beams are cheap, so doubling up with some cross braces shouldn't be a big deal. In fact an approach like this might be the most reasonable in terms of cost/complexity/turnkey materials.
Re: Tripteron Implementation
January 07, 2017 10:16PM
Here's what I have in mind for delteron's elbow joints:


This doesn't make the best use of having two arms as they're still right next to each other, but the cross-sectional bending stiffness is easily greater than a 15x15 extrusion. In return, torsional stiffness can be brought up to similar levels by closing out or trussing out the space between the beams with printed gussets. Reducing to a single beam for the 'forearm' should cut weight around the effector and simplify the interface.

Leaving the hinge anything less than tight will result in large amounts of backlash since the angular clearance gets magnified across the arm's length, so I'm going to try adding slippery washers to act as thrust bearings. The hinges are actually one of the more expensive parts at $3-4 per joint, similar to the m3x10mm shoulder bolts. The yellow part in the picture is a cheap M2 x 8mm brass standoff to clamp the joints to that should also assist with align the axes. It would be bottomed out against only the upper joint because the hinges are symmetric and don't have mirrored versions.

Parts are on their way but shipping the hinges from Germany could take up to 4 weeks... Meanwhile I'm going to try to cobble together a delta frame from a side table - a half finished project of mine which could serve as a test rig and eventual delteron.

Edited 1 time(s). Last edit at 01/08/2017 08:51AM by brazenrain.
Re: Tripteron Implementation
February 02, 2017 09:55PM
Small update- I built assembled the aforementioned joint, but I overestimated how well aluminum-on-aluminum friction would hold. The beams themselves feel strong enough at 400mm total arm length, but the bolts won't stay put through a series of movements. It could be made to work by the right sequence of bracing, but then the alignment depends on the repeatability of printed plastic parts. For now I'm stowing the 10mm beams away- maybe for a sarrus linkage z-axis later on.

I also discovered that mcmaster had these for 20mm extrusions all along, which I might try next right after I push through to a working gantry for my cantilevered y-axis concept. I'm close to finishing the design without any printed parts but need to make sure it's stable enough running actual gcode to be worth carrying forwards.
Re: Tripteron Implementation
June 29, 2017 04:19AM
Hey Apsu.. smiling smiley

Im building your tripteron, but i have a question of where you placed the endstops.. smiling smiley

I have Now printed all the parts and ordered rails.. I redesigned the z-axis slightly to use a leadscrew instead
Re: Tripteron Implementation
September 02, 2017 02:43AM
Hi Apsu,
I'm afraid that you've probably abandoned this project, but just in case...

In one of your early updates to this project you stated: "The angle between the actuators and the arm joint plane is something that can be tweaked as part of the engineering considerations. Larger angles give more resolution at the cost of less max Z height (actuators move up/down more for a given X/Y motion), while smaller give less resolution but gain Z height." Can you please explain that a little more? I'm having trouble visualizing which angles you are talking about, and how they affect Z-height.

Also, how does arm length play into this?

Anyway, sorry to see this thread go dormant. Lots of good info here.
Cheers,
Scotty

Edited 1 time(s). Last edit at 09/02/2017 02:44AM by scottyo.
Re: Tripteron Implementation
September 02, 2017 09:23AM
Hey Scotty,

That was referring to the second design I began working on, where there's an angle the actuators are rotated with respect to the arm joints. The actuator arms have 3 joints -- actuator-arm, arm-arm, arm-effector. So really when I say "joint plane" I mean that those three joints are all aligned the same. However, how the two end joints attach to the actuator and the effector has a fixed angle like 30deg, for instance. You can adjust this angle a bit up/down around that value and it results in what I said. A smaller angle (closer to 0deg, or in-line with the arm joint plane) means that the same actuator motion (up/down) results in the same effector movement as a higher angle would with more actuator motion.

The tradeoff is a loss of resolution, because the relationship of the arm angle to resolution boils down to a simple ratio that varies only by that angle value. Likewise, higher angles give higher resolution but require more actuator motion for the same effector motion (higher ratio) -- practically this means you have less Z space to move in at the extreme top/bottom range, since you'll hit the end of the rails "sooner" to achieve the same amount of build space coverage. This is all assuming you're trying to maintain the same build area at every point in the build volume.

Hope that helps! I'm still around, even if not working on this anymore, so feel free (you or anyone else reading) to hit me up if you like. To be honest, I tend to jump between my hobbies every 6 months or so and this was a new one to me, so I dug in deep for awhile and now I'm back to music and gaming, but that doesn't mean I have no interest, I'm just not spending time on it right now smiling smiley

Edited 1 time(s). Last edit at 09/02/2017 09:24AM by Apsu.
Re: Tripteron Implementation
September 02, 2017 09:23AM
Arm length needs to be just long enough to reach across the work volume. A smaller angle will allow the arms to be shorter. The flex of the arms is proportional to length^3 so you definitely want to minimize it.


ConceptFORGE
Wally, GUS Simpson, LISA Simpson, THOR Simpson, Sextupteron, CoreXZ
Re: Tripteron Implementation
September 02, 2017 10:30AM
Thanks - both of you!
The application I am designing for will not require much z-height. Also I am looking at a variation of the "other" of the three implementations listed in the paper.
(The one attached below.) However, I am thinking I will probably incline the actuator rails a bit (and maybe flip it upside down - a shallow tetrahedron).
Thanks again,
Scotty

Edited 1 time(s). Last edit at 09/02/2017 10:39AM by scottyo.
Attachments:
open | download - Tripteron.png (224.5 KB)
Re: Tripteron Implementation
September 02, 2017 10:44AM
I should add, I think a taller tetrahedron (with actuators underneath the arms) would be a good model for a 3-D printer, but that's not where I'm starting.
Re: Tripteron Implementation
September 14, 2017 12:06PM
Admin note: please avoid using foul language. This is a warning. Thank you.

Edited 1 time(s). Last edit at 09/14/2017 01:31PM by NewPerfection.
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