## Challenge: Constant Velocity Joint (M. Gesik)

Discussion about the development of the Assembly workbench.
Zolko
Posts: 843
Joined: Mon Dec 17, 2018 10:02 am

### Re: Challenge: Constant Velocity Joint (M. Gesik)

ppemawm wrote:
Sun Mar 22, 2020 3:25 pm
I do not know yet if ASM4 can articulate the CV joint so may need ASM3 sooner than later.
To be honest, I wouldn't know how to assemble that using Assembly4. I did a classical cardan joint, and you can see that it's not a constant velocity transmission. In this case, it's mathematically exact, so you can even set the deflection angle to 89° and it'll still work. Now, how to do the same with that complex setup .... ? Generally speaking I have experienced that you need to be able to describe mathematically the model for Asm4 to be able to represent it. In this CV joint case, I don't understand how it works, which parts are fixed, which move ...

Now, as with the hexapod, if you accept to "cheat", meaning that you suppose that it is a constant velocity joint, and you impose the exit arm to have the same rotation angle as the input arm, and the middle part to have a deflection angle 1/2 of that of the exit arm (which is given by the gears), it might be easier. But then, you won't be able to check that it is indeed a constant velocity joint.

Cardan_Asm4.png (368.57 KiB) Viewed 571 times
Attachments
asm_Cardan.FCStd
try the Assembly4 workbench for FreCAD v0.19
install with Tools > Addon Manager > Assembly4 — tutorials here and here
jruiz
Posts: 220
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Contact:

### Re: Challenge: Constant Velocity Joint (M. Gesik)

Kunda1 wrote:
Sat Feb 29, 2020 3:24 pm
phpBB [video]
source: https://www.reddit.com/r/mechanical_gif ... ity_joint/
Thingiverse: https://www.thingiverse.com/thing:4191753
After watching the video I googled a little and found the following article (date of publication: August–October 2009) that could be of interest to some of you:
A new kind of spherical gear and its application in a robot's wrist joint

ppemawm
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Location: Manhattan New York

### Re: Challenge: Constant Velocity Joint (M. Gesik)--UPDATE #2

Zolko wrote:
Sun Mar 22, 2020 6:12 pm
To be honest, I wouldn't know how to assemble that using Assembly4.
The CV joint assembly has been completed as far as I can go with Assembly4:

This is a view of all the interconnected parts using the local coordinate systems (LCS) provided by Assembly4. The LCS were attached to model edges so it is prone to topological problems if any features are changed.

Assembly4 provides a very convenient means for attaching hole LCS's, as well as selecting and adding fasteners to the model. Not all of the fasteners, circlips, or bearings are shown in this image.
.
Picture5.jpg (107.48 KiB) Viewed 474 times
The last three (3) joints (see arrow) of the top 3-legged ring could not be assembled with Assembly4 since it has no solver. AFAIK it is not possible to "close the loop" of all the interconnected parts using Assembly4 without a circular dependence.

The geared links as shown were approximately aligned using the Part > Link Attachment Offset properties.
.
Picture6.jpg (117.78 KiB) Viewed 474 times
.
Perhaps a master sketch approach similar to that used by OficineRobotica's hexapod may be a solution:

That is what I will research next unless Zolko can offer any other suggestions....not quite ready to give up after spending so much time on creating the parts.
"It is a poor workman who blames his tools..."
Zolko
Posts: 843
Joined: Mon Dec 17, 2018 10:02 am

### Re: Challenge: Constant Velocity Joint (M. Gesik)--UPDATE #2

ppemawm wrote:
Wed Mar 25, 2020 7:10 pm
Zolko wrote:
Sun Mar 22, 2020 6:12 pm
To be honest, I wouldn't know how to assemble that using Assembly4.
The CV joint assembly has been completed as far as I can go with Assembly4:
Nice. I tried my luck also, but without success either. I used the STL files as they came, and reverse-engineered their geometrical attachment points. Then, I tried to calculate the relevant attachment points in the assembly, but I'm stuck: I would need the result of the intersection of a surface (a cylinder) and a curve. Unfortunately, I cant attach the files themselves because they're too big. I could provide the skeleton, but since it doesn't work it's not of much use.

CV_joint.png (545.4 KiB) Viewed 461 times
try the Assembly4 workbench for FreCAD v0.19
install with Tools > Addon Manager > Assembly4 — tutorials here and here
Zolko
Posts: 843
Joined: Mon Dec 17, 2018 10:02 am

### Re: Challenge: Constant Velocity Joint (M. Gesik)--UPDATE #2

Zolko wrote:
Wed Mar 25, 2020 8:12 pm
I would need the result of the intersection of a surface (a cylinder) and a curve.
gotcha ! I got the help I needed, and so could build a working skeleton and assembly:

CV_joint.png (527.11 KiB) Viewed 409 times

This is now an exact solution, exact to the point that I don't really know the real dimensions of the parts, so I had to guesstimate these dimensions. But it behaves correctly from -40° to 40° deflection, and full 360° rotation.

ppemawm wrote:
Wed Mar 25, 2020 7:10 pm
The CV joint assembly has been completed as far as I can go with Assembly4:
If you want to assemble your parts (which are much nicer) with my method, I attach the skeleton, which is the assembly where I have simply removed the parts. Parts are attached to :

CVJoint_parts.png (840.15 KiB) Viewed 409 times
CVJoint_skeleton.png (360.19 KiB) Viewed 409 times

The pictures show where the attachment LCS are in the respective parts:
• bielette_A to LCS_arm_A_1
• bielette_B to LCS_arm_B_1
• liaison_10_3 to LCS_common
• corps_lisse to LCS_input and LCS_output, BUT: these must be offset in the AttachmentOffset in the Z direction by 45mm and -45mm
And you have to play around with the RotX-RotY-RotZ buttons, obviously
Attachments
skeleton_CVjoint.FCStd
try the Assembly4 workbench for FreCAD v0.19
install with Tools > Addon Manager > Assembly4 — tutorials here and here
ppemawm
Posts: 645
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Location: Manhattan New York

### Re: Challenge: Constant Velocity Joint (M. Gesik)

Zolko wrote:
Thu Mar 26, 2020 10:15 am
...I attach the skeleton...
Thank you for that. I have been thinking too much in two dimensions. There is much to study in your file.
I will try to apply it to my model parts over the next week or so.

Genius you are, once again.
"It is a poor workman who blames his tools..."
aapo
Posts: 103
Joined: Mon Oct 29, 2018 6:41 pm

### Re: Challenge: Constant Velocity Joint (M. Gesik)

Hi,

This looks very very interesting, and seems to be quite an achievement! Congratulations Zolko and ppemawm! Would it be possible to include this in the FreeCAD examples, please? Section "Beyond Advanced"
jpg87
Posts: 395
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Location: Limoges - France
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### Re: Challenge: Constant Velocity Joint (M. Gesik)

ppemawm wrote:
Sun Mar 22, 2020 3:25 pm
I do not know yet if ASM4 can articulate the CV joint so may need ASM3 sooner than later.
HoWil wrote:
Sun Mar 22, 2020 7:47 am
Can you please elaborate on why you use ASM4? Never used it until now but I would have used ASM3 without thoughts.
Zolko wrote:
Thu Mar 26, 2020 10:15 am
gotcha ! I got the help I needed, and so could build a working skeleton and assembly:
Hi
this weekend I couldn't resist the urge to try this mechanism with Asm3 WB.
Here's what I get.
CardanHomocinJpg87.png (80.18 KiB) Viewed 244 times

Animation video:

My website : http://help-freecad-jpg87.fr updated 2020/05/10
chrisb
Posts: 24281
Joined: Tue Mar 17, 2015 9:14 am

### Re: Challenge: Constant Velocity Joint (M. Gesik)

Great video! Perhaps it would be even more convincing if shown at a motion angle of 45°.
jpg87
Posts: 395
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Location: Limoges - France
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### Re: Challenge: Constant Velocity Joint (M. Gesik)

chrisb wrote:
Mon Mar 30, 2020 2:04 pm
Perhaps it would be even more convincing if shown at a motion angle of 45°.
I remade the video by simultaneously varying the angle between the entry and the exit from 25 ° to 41.8 °: we then see that the arms with toothed sector collide (see more?).
My website : http://help-freecad-jpg87.fr updated 2020/05/10