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View Full Version : what do you use for universal joints?



aggrav8d
06-13-2013, 01:08 AM
I've been using heim joints on my stewart platform

http://www.youtube.com/watch?v=rhuM6Cnn5Pk

and my delta robots

http://www.youtube.com/watch?v=7AchUoL9qdo

but they limit the range of motion. I'm looking for a universal joint sized for M3 screws and threaded rod. Do you know of a supplier, or an equivalent? I've been searching Alibaba for likely candidates with no luck.

I also have access to a prusa 3D printer and a laser cutter. I could manufacture a part if you've got a suggestion.

CasperH
06-13-2013, 01:52 AM
To my knowledge, IGUS has some of the "largest" positioning angles joints. This K series has 40 degrees: http://www.igus.com/iPro/iPro_02_0030_0000_USen.htm?ArtNr=kclm-06&c=US&l=en

Another alternative I saw recently at a robot event for professional delta robots was the use of two balls and clamped around that 2 cups on each side that are held together with a spring. I can't find a picture, if needed I can draw it for you.

jwatte
06-13-2013, 12:50 PM
Two Y stirrups and a plus in the middle will make a universal joint with large range of motion, although you're never going to get more than 90 degrees each way, minus interference. If you need low friction (bearings) and strength, interference is going to be significant.

Simple illustration (exaggerated for clarity):

4800


I know that you can get some of these from RC hobby car axles, and perhaps from heli rotor axles as well?


Btw: That igus page is annoying! Using gigabit internet at work, it still took 30 seconds of "please wait for the entire page to download," which is pretty much a "worst practice" in web development...

CasperH
06-14-2013, 01:20 AM
aggrav8d, I forgot to ask, how much movement are you looking for and what kind of load bearing?


Btw: That igus page is annoying! Using gigabit internet at work, it still took 30 seconds of "please wait for the entire page to download," which is pretty much a "worst practice" in web development...

Odd, it takes me about 1 second. Which is a bit long I admit, but not that long.

jwatte
06-14-2013, 12:00 PM
Btw: Those igus joints are what I would call "ball joints" -- they look like they have three degrees of freedom. A "universal joint" is a joint with two degrees of freedom (see illustration.) And if someone has a good bead on a supply of those other than scavenging from RC car axle linkages, I'd be interested in hearing about it :-)

escott76
06-14-2013, 01:48 PM
McMaster, smallparts, SDP-SI all have some. When those fail to give me what I want I know a guy with a mill...

aggrav8d
06-14-2013, 02:38 PM
I'm looking for....
- 2 degree of freedom with at least +/-45 degrees range of motion. +/-90 would be fantastic.
- 1kg weight limit
- M3 mating
- off the shelf availability and/or bulk pricing.
- able to mate to https://www.sparkfun.com/products/10976 would be cool. I can make an adapter.

I'm also looking for a u joint with a 50kg weight limit and mating in the M6-M8 range.

I'm in Canada. All my attempts to order from McMaster Carr have been rejected. Never heard of a business that wanted me to shop somewhere else.

escott76
06-14-2013, 02:49 PM
M3 Mating? Meaning the ends are tapped? Or meaning that the ends are bored to 3mm round? One is going to be easy, the other not so much.
+/-90 isn't going to work in a single joint, you will need two of the wishbone type to get to 90.

jwatte
06-14-2013, 05:59 PM
+/-90 isn't going to work in a single joint,

You can get close. The trick is to make sure that the hollow in the wishbone is deeper than the plus/x is wide.

The SDP-SI ones were all of the < 20 degree kind, and the plus-type ones were 3 degrees or less.

Here's an idea: How about a simple sheathed cable that can bend? Does the joint need to be rigid in the longitudinal direction?

tician
06-14-2013, 06:18 PM
Just to clarify, are these to be transmitting power (motor shaft) or just supporting weight (joint in delta robot)?

A non-power transmitting (non-rotating), 2DOF, wide-angle swivel joint could easily be constructed with hand tools using jwatte's drawing as a basic reference.

A power transmitting, wide-angle universal joint is a bit harder to accomplish. If transmitting torque at weird angles is the only requirement (not providing structural support), a flexible drive shaft might be an option (make or buy).

aggrav8d
06-15-2013, 06:42 PM
tician -

For delta robots like (http://bit.ly/ZCeFUu) I don't have to worry about the 3rd degree so I'm looking seriously at some magnetic ball joints (http://bit.ly/19DK6li). Don't know what kind of wear they'll go through. I'm looking for the best possible price - in my simplest robot I use 12 units, in the next model up I use 16.

For Stewart Platforms I'm looking for smooth-bore with set-screw. M4 might do. Thingiverse has http://www.thingiverse.com/thing:3140. I found these (http://bit.ly/19DKrEG). I haven't tried either yet. I'm looking for a better price as I'd rather buy off the shelf than manufacture. Until I can afford to manufacture I'm forced to stick with using ready-made parts.

I'm also comparing note to see what anyone else found.

jwatte
06-15-2013, 10:09 PM
Those look like a great option!

CasperH
06-16-2013, 04:05 AM
Btw: Those igus joints are what I would call "ball joints" -- they look like they have three degrees of freedom. A "universal joint" is a joint with two degrees of freedom (see illustration.) And if someone has a good bead on a supply of those other than scavenging from RC car axle linkages, I'd be interested in hearing about it :-)

Yes, you are totally right. I guess it was a bit too early in the morning when I wrote that reply. :eek:


tician -

For Stewart Platforms I'm looking for smooth-bore with set-screw. M4 might do. Thingiverse has http://www.thingiverse.com/thing:3140. I found these (http://bit.ly/19DKrEG). I haven't tried either yet. I'm looking for a better price as I'd rather buy off the shelf than manufacture. Until I can afford to manufacture I'm forced to stick with using ready-made parts.

Myself, I usually get these kind of things at RC hobby (web) stores. As like your second link. They usually do have quite some margin for themselves, so if you want to go bulk better find a supplier for the more professional crowd.

You can also try here: https://sdp-si.com/eStore/CoverPg/UJoints.htm