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ball-cap rod-end concept pros and cons

Posted by shadowphile 
ball-cap rod-end concept pros and cons
September 09, 2017 12:44AM
Hello, after custom machining my effector and carriages I am now frequently getting .01 mm auto-levels on a machine with a 300mm print space, which I am pretty happy with.
However, the Traxxis rod-ends are definitely the weak link (no pun intended!) and I'm looking at alternatives.
The magnetic ball approach seems popular and easy to make accurate but I just don't trust magnets and shudder when I imagine my untended printer smashing itself to pieces.
Instead I recently learned about the ball-cap approach: the balls are mounted axially on the effector and the rod-ends are shaped to cap laterally on the ball, with a spring pulling the rod ends together.

My thought is that making the ball-cap end precisely centered on the ball itself is important, otherwise the effective rod-lengths will change with angle.
So far I have only encountered this design at Trick Laser
The parts are injected-molded Delrin so the accuracy is probably really good and likely to stay that way, IF you can find 3/8" ball studs. Most ball-studs I can find are 10mm, which differs from the Trick Laser parts by about 5%. Damn Americans using imperials units! (I am a damn American btw). A short ball-stud would directly replace the traxxis ball without any redesign (assuming the same M3 stud).

So far I have not found much hands-on or theoretical discussion of this idea so I am starting one now.
thanks
Re: ball-cap rod-end concept pros and cons
September 09, 2017 02:23AM
In another thread I read about IGUS-filament. If you have a working printer, you can try to print your own ball caps. Maybe make them fit with heat?
BTW: Many Deltas run on original IGUS ball ends, but they are expensive.
Re: ball-cap rod-end concept pros and cons
September 09, 2017 03:45AM
I recommend the magnetic rods and ball studs by Haydn Huntley. They have never come apart on me except when I applied force to the effector manually.

I've never used ball-end axles and caps, but user saffi on the Duet3D forum has used both the SeeMeCnc and the Tricklaser ones I believe and may be able to offer some advice. Here is one of saffi's posts: [www.duet3d.com].

Edited 1 time(s). Last edit at 09/09/2017 03:46AM by dc42.


Delta printer calibration calculator, mini IR Z probe, and colour touch screen control panel: [escher3d.com]

Large delta printer, and other 3D printer blog postings: [miscsolutions.wordpress.com]

Disclosure: I have a financial interest in sales of the Panel Due, Mini IR height sensor, and Duet WiFi/Duet Ethernet.
Re: ball-cap rod-end concept pros and cons
September 09, 2017 07:51AM
Haydn also sells 3/8 Ball studs separately Haydn's Ball studs
Re: ball-cap rod-end concept pros and cons
September 10, 2017 04:05PM
Would not be too hard to machine something that works like the Trick Laser-cups, I think. A countersinked hole in some slippery, reasenably hard material should do it. The trick is attaching the spring so the joints will self-center. A pure print might work too

Edited 1 time(s). Last edit at 09/10/2017 04:06PM by SlowFoot.
Re: ball-cap rod-end concept pros and cons
September 11, 2017 04:56AM
or machine it with a 3/8 ball mill
Re: ball-cap rod-end concept pros and cons
September 11, 2017 01:36PM
Go with Haydn's rods. You can order them on ultibots, they're fairly priced and outstanding.
Re: ball-cap rod-end concept pros and cons
September 12, 2017 09:03AM
+1 for Haydns magnets they won't disconnect unless you have a catastrophic impact with something and then you probably want them to.

They have zero backlash and are light.

My only suggestion would be thicker carbon rods/tubes for longer lengths I. E. 360mm plus as I can slightly bend my 360mm arms if I try, not that it seems to cause any practical issues, it just seems to make sense as length increases to increase stiffness.

Edited 1 time(s). Last edit at 09/12/2017 09:04AM by DjDemonD.


Simon.

[www.precisionpiezo.co.uk] Accurate, repeatable, versatile z-probe plus piezo discs, endstop cables, pt100, 50w heaters. PT1000 cartridge sensors plug straight into duet boards and others.
Published:Inventions
Re: ball-cap rod-end concept pros and cons
September 15, 2017 07:49PM
thanks for the input. I still have a conceptual problem with the magnets. They get weaker as you pull away vs springs that get stronger as they stretch. The later sounds more shock resistant.
Re: ball-cap rod-end concept pros and cons
May 14, 2018 03:00PM
Hey did you ever end up going for the trick laser arms? I'm curious about that option because it seems much lighter than the magnetic arms and the magnets are causing problems with the fan for my cold end.
Re: ball-cap rod-end concept pros and cons
May 14, 2018 03:40PM
Hi warbunniex.
I've been using the Trick Laser parts for a while. As expected they have great zero-backlash so the performance has been good.
Some things I have learned though:
-The springs required to pull the arm-ends together can get in the way of the either the carriages or the effector, depends on your designs. I like the springs in general for disassembly but their presence is really a con in the custom design of my own machine.
-The mounting axis of the balls must be lateral. For mag-ball rods, the mounting axis of the balls must be upright. They are incompatible so not easy to swap over without a redesign.
-I had no problem finding the correct ball size (Hadyns).
-The ball-cap design has to be very precise as the rotation center is in the middle of a hollow. The magnet-ball ends just have to be well centered which is a lot easier to fabricate. I'm sure Trick Laser knows this and has a precise design but I would have to build a test apparatus just to measure for myself.
-The Trick Laser rod-ends use little loops molded into the rod-ends to hold the spring ends.. They seemed fragile to me though and sure enough I had a metal extrusion fall on my effector and break one of the loops. I've been running with a pair of tiny cable-ties to hold the end of the spring (and the second tie to keep it from riding up the length of the arm). I suggested to Trick Laser they either remove the loops, or add in the ability to use a cable tie for the rod end (without allowing it ride up the rod), as cable ties are replaceable and generally tough (albeit not as pretty).
-The Trick Laser design also has pulling forces that do not align with the ball-cap center, which will cause the rods to bow together to some small degree. Another approach that pushes along the ball's mounting axis would be ideal (like a spring clip that presses on the backside of the rod end). The offset force also seems hard on the attachment of the rod-end to the rod cause it pulls sideways. The mag balls only direct tension in the same direction as the rods themselves.

Given the general interference of the springs, the non-ideal assymetric forces, and the fact that the increasingly-popular mag ball approach has not been reporting gripping problems I am designing my next effector platform for the mag-ball approach.

You have a fan on your cold end? I can't easily picture how a magball would cause a problem. Their are also ways to shield against magnetic fields although I can't comment on the effectiveness in this application. Google mu-metal or mu-shield for sources and tech details.

Hope this helps!
Re: ball-cap rod-end concept pros and cons
June 15, 2018 06:17PM
If your only concern before was the magnets becoming detached then try them. They work very well, and if it does come apart it will be a good thing, less damage will occur as the effector will stop crashing into things and just wobble back and to attached to the 2 or 3 arms which are not disconnected.


Simon.

[www.precisionpiezo.co.uk] Accurate, repeatable, versatile z-probe plus piezo discs, endstop cables, pt100, 50w heaters. PT1000 cartridge sensors plug straight into duet boards and others.
Published:Inventions
Re: ball-cap rod-end concept pros and cons
June 16, 2018 03:48AM
Shameless self-promotion: so use Zatsit's polypropylene hinged system, which is ultra-light, extremely accurate without any adjustment, and performs very well against ringing.

Look at the photo I published on this post:
[reprap.org]

Edited 1 time(s). Last edit at 06/16/2018 04:16AM by M_Xeno.
Re: ball-cap rod-end concept pros and cons
June 16, 2018 04:59AM
Quote
M_Xeno
Shameless self-promotion: so use Zatsit's polypropylene hinged system, which is ultra-light, extremely accurate without any adjustment, and performs very well against ringing.

Right... so when/where can I get it?
Re: ball-cap rod-end concept pros and cons
June 16, 2018 05:29AM
Soon on Kickstarter, online after. Take a look at www.zatsit.fr
Re: ball-cap rod-end concept pros and cons
June 16, 2018 05:31PM
Can you give us an idea of what "soon" means? A day? Week? Month?

I've been checking KS daily since I saw your first post!
Re: ball-cap rod-end concept pros and cons
June 16, 2018 08:00PM
I checked the Zatsit site and it seems like a great novel approach. One thing about 3D printing that fascinates me is how fertile it is for innovation. Like the very early days of computers.

My only complaint about the Hylite material is that it's no good for us without access to a precision 2D router table. Buying that service would get expensive and any time I need to make a small part I can't do it myself. So for hobbyists it seems useless, but great for engineering a device at low cost and high performance for those willing to invest into something that will return the costs, like Zatsit.
Re: ball-cap rod-end concept pros and cons
June 17, 2018 01:22AM
Quote

So for hobbyists it seems useless...[Hylite]

I thought the same, but VDX already made an remark about using PP as hinges and clamp it in you own design.
If we'd find a way to glue or bond PP to a printed part or aluminum surface, we wouldn't need milling machines.

Edited 1 time(s). Last edit at 06/17/2018 01:22AM by o_lampe.
Re: ball-cap rod-end concept pros and cons
June 17, 2018 05:23AM
@o_lampe, shadowphile, VDX

Hinges to glue: that's a very good idea!

During the KS campaign, I will propose, among the goodies offered to bakers who want to support the project, but do not want to buy a complete kit, hinges ready to glue.

For example, a Ø30mm disc, with one hinge along a diameter, and another, with two perpendicular hinges, to make a joint.

This would allow Makers to easily integrate this technology into various DIY projects. I could also sell that stuff online after the KS campaign, next to Zatsit, and other Hylite applications.

But if it is to make a linear delta robot, believe me, nothing will ever be worth the simultaneous cutting of all the hinges of an elementary deformable parallelogram, as the Zatsit kit proposes it!

Edited 1 time(s). Last edit at 06/17/2018 05:28AM by M_Xeno.
Re: ball-cap rod-end concept pros and cons
June 17, 2018 01:19PM
For KS backers make a badge from Hylite with a 'Z' engraved smiling smiley
Re: ball-cap rod-end concept pros and cons
June 17, 2018 06:10PM
Sounds good, I can see buying modular pieces.
It seems to have a limited strength though. I'm designing version three of my delta to carry multiple extruders and swappable with other types of hot-ends so the entire frame is getting thicker parts which will load the joints more when trying to go fast. I can't seem to avoid designing away from light airy printers that can move really fast.
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