Hey! This thing is still a Work in Progress. Files, instructions, and other stuff might change!

Delta Bearing U-Joint

by tempo502 May 26, 2015
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Can you publish the efector that you use for this type of joints? (I see it in the images) . thanks in advance

Can I ask for some extra pictures:

Like all the parts dis-assemled (bearings included) laid out how they assemble.

And do you use these joints only on the print head plate, or do you also use these joints at the other end? I can't tell in the picture.

If you use something else at the other end what do you use?

It's pretty self-explanatory once you have the parts in front of you. Print two inner yoke pieces and two outer yoke pieces. Stick four bearings into the bearing pockets. Take the two inner yoke halves, and put them face-to-face (ie print bed side together). Stick the protruding shaft nub into a bearing for one side of the outer yoke. Repeat with the other outer yoke. Then either glue or bolt the two outer yoke halves together around the rod.

You definitely want to use the same joints at both ends of the rods, to help ensure you get everything parallel.

hi there
what about the file for the effector? sharing or no?

I'm going to post the effector files with the associated printer design... I just haven't gotten around to it yet, sorry.

I think your design for the uni joint is very cool, I printed half a piece, but the bearing does not fit. Can you tell me what CAD program you use?

The .skp Sketchup source file is attached in the files here. There's also an OpenSCAD remix: https://www.youmagine.com/designs/delta-u-joint-for-ball-bearings

The pocket is 10.11mm minimum inside diameter in the model, so a 10mm OD 623 bearing should fit tightly on most printers. It takes me some effort to get the bearings in, and I recommend printing in ABS or PET because PLA is too stiff. If it still doesn't fit then you may want to tweak your print settings.

Alternatively, just scale up the part by a few percent until it fits. Shouldn't cause any problems on the outer yoke pieces. The inner ball parts probably shouldn't be scaled up though.

is a 693zz 374mm or a 683zz 384 mm bearing enough to take the load ? with these the weight and size can be reduced

They're probably strong enough, there shouldn't ever be more than a few tens of newtons per bearing.

I love the Kossel Pro arm swivels and I'm glad you took on the design challenge - with that said I'd like to see this thing work and be smaller as well.

What about bearings like these http://www.ebay.com/itm/Silver-Tone-Metal-Sealed-Deep-Groove-Radial-Ball-Bearing-1-5mm-x-4mm-x-2mm-/130909621815?pt=LH_DefaultDomain_0&hash=item1e7ad24e37

I have purchases some of the same style of these for model railroading uses and they work really well. You might be able to just shrink your design?

There's an OpenSCAD remix of this design that you're welcome to try for custom bearing sizes: https://www.youmagine.com/designs/delta-u-joint-for-ball-bearings

The challenge with simply scaling the design down is that you run into issues with wall thicknesses and cross-sections that are reasonable for FDM printing.

Personally, I don't have a problem with the size of this U-joint. If you want small, I'd recommend sticking with Traxxas joints. The design objectives here were using a common bearing size that fits M3 hardware, and providing a high degree of stiffness. I'm building a bot around these arms and it's a slam dunk for meeting the design goals.

Nice! I considered making something similar, but the weight of 8 bearings per arm made it seem like a bad idea. Let me know how it goes!

My thought is that the added stiffness because it's a U-joint and not a spherical joint should offset the extra weight. But I need to build a bot around it to find out!

Hmm, you're right, I hadn't considered that aspect -- I was only comparing it to the original rostock rod-ends, which only have the weight of a bunch of screws and nuts in addition to a smaller volume of plastic than this piece.

One thing that might be a bit of concern is the range of motion it has. When I made my initial batch of rod-ends, I noticed that the thickness caused it to be less flexible at certain angles, so I reduced its thickness back to the original rostock thickness. In comparison, the Delta-Pi's u-joints, which do not have crossing axes, seem to have solved this problem pretty nicely.

Parametric rostock rod-end printed u-joint jaws for hollow tubes

I like the Delta-Pi approach, it's a good mechanism as long as the parallelogram joints are colinear with the axis of the carriage rotary joints. That's necessary for the effective rod length to be constant as the arms move through their range of motion. I considered going that way (and still might) but I have a specific application in mind that requires this traditional Cardan-joint style U-joint design.

Each joint weighs about 15g, versus 3g for a traxxas joint plus 20mm M4 set screw, so you're adding ~70g to the effector in total with six rods. My current traxxas joint effector w/ E3Dv6 and blower fan (sans rods) is about 120g. So yeah, it could be a meaningful amount of extra weight. Still pretty light compared to a direct-drive extruder motor though.