How to assemble/animate barrel cam

[ANilsson50]

See screenshot below for reference.

I have a situation where I need to move vertically and rotate at the same time and I cannot find the correct joint combinations to make this work.  As seen in screenshot, the 2 rods move up and down in the barrels.  As they move, there is s pin in each rod that follows a cam slot in the barrels.  Moving down, the 2 rods should rotate 180 degrees in opposite directions as they each follow their own cam slot.

There are rotational joints at the interface between each rod and the rod cap and they work correctly.  I cannot work out how to make the pins follow the multidirectional cams and there is no rotation of the rods as they move.

The slots in the barrels were made by embossing a sketch on the cylinders if that matters.

Help appreciated!

[jeff_strater]

try the "Tangent Relationship" in the assembly menu.  I cannot say I have explicitly tried this type of cam, but cam motion is what it is designed for.  The rods will have to have a cylindrical joint in order to both translate and rotate.

[jhackney1972]

I would love to experiment with your assembly.  I have been studying and using the new Tangent Relationship since it was introduced with good success.  Your type of assembly will be a good test.  Could you share it?   If you do not know how to attach your Fusion 360 model follow these easy steps. Open the model in Fusion 360, select the File menu, then Export and save as a F3D or F3Z file to your hard drive. Then use the Attachments section, of a forum post, to attach it.

[ANilsson50]

No dice.  there description says it relates one face on the first component to a series of connected faces on second component but it only relates to one face on second component.  The operation does not let me select multiple faces, only 1.  It appears to work for that 1 face but the slot in the tube is composed of multiple faces and movement is only allowed to slide on the one face selected.

[jhackney1972]

I agree the Tangent Relationship will only select one face of your slot but if all the faces are tangent, it will normally bridge from the one your select.  Could you attach your model as requested earlier?

[ANilsson50]

its not easy attaching model - I would have to remove some proprietary components.

I am still worried about how I created the slots in the tube and that it may be causing problems.  What would be the canonical way to do that?  I created a tangent plane to the tube, created a sketch on it with 3 end to end slots then 'embossed' that onto the tube.

[jhackney1972]

I would create the slots using a surface sweep with a twist.  Then you can use the Thicken command to create the slot using the surface sweep as a path.  I would use the Pipe command to make the ends round using the surface sweep as a guide.  An example model is attached.

By the way, you are selecting the Quick Reply icon which replies to yourself.  Use the Reply icon to reply to the poster you are addressing.

[ANilsson50]

I am trying your solution to create a sweep.  Looking at your sample, I cannot get the sweep tool to recognize the horizontal as the profile when trying in a new design.  It doesn't look like you have a separate horizontal plane sketch.  How does the sweep tool determine that the line is acceptable as a profile?

Second, using this technique, how would one account for the 2 vertical sections at the ends of the slot?  Essentially the slot is 3 sections, vertical, 180 degree sweep, then vertical again.  would this be 3 separate sweep operations?

[jhackney1972]

I created another model with the two straight sections with a .75 in radius between the spiral section and the straight sections.  I walked through the process in a Screencast so I hope that helps you understand the process I used.  For a Surface, either for the Sweep surface or the Extrude surface, the profile is a line.

On the subject of the Tangent Relationship, I have been experimenting with this and so far have not had a lot of luck with a cylinder and pin following this tube path but I am in the early stages of experimentation.

[TheCADWhisperer]

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@ANilsson50 wrote:

I am still worried about how I created the slots in the tube

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Emboss will not result in correct geometry.

[wersy]

I like the idea of making the slot by thickening the surface.
Could you also animate the movement as desired?

[MADCannon0077]

Wanted to test this out and also check tangent relationship since I never had a chance to use it in my projects. Thanks for the sweep idea and tutorial @jhackney1972 , it was nicely done.

Back to the issue at hand, all I managed was what is shown in the attached gif picture. Fusion is almost doing it right, I mean, component pin is getting properly constrained to be tangent to the wall of the slot but on the outside. Sometimes it goes back inside the slot tho.

Oh well, I ll keep trying.

[jeff_strater]

@MADCannon0077 - would you be willing to share this with us?  I think the development team would be interested in this model, especially the flipping to the outside.  It does look close, though!  Thanks.

[MADCannon0077]

Sure thing.

I've been troubleshooting it a bit more and found out the problem is the slot's fillet. If I supress or remove the fillet, the pin component does not move tangent to the outside perimeter of the slot anymore. However, the bad news is that I am back to square one since it barely moves, or it does then gets stuck.

Attached are both projects.
Thank you.

[ANilsson50]

My thanks too @jhackney1972.  That was very informative.  My problem was I was not using a surface sweep when I first tried.

It is disappointing that the the motion is not working for anyone.  This seems to me a non novel design idea.

If anyone figures it out please speak-up.

[TheCADWhisperer]

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@ANilsson50 wrote:

It is disappointing that the the motion is not working for anyone. 

If anyone figures it out please speak-up.

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@MADCannon0077 

Nobody has modeled the slot correctly yet.

Examine the Attached file.

https://www.youtube.com/watch?v=Wekmai5MqFM

https://www.youtube.com/watch?v=qKAeO00Qd5A&list=PLp5izJt_zvN08mpY4UcYrzJV2N6QOLAIR&index=23

[jhackney1972]

Your YouTube video may show a different method of making the cam slot but you used the same slot we have been using.  What you did was to add a surface sphere inside the follower pin and used that to create the tangent relationship.  This gives single point contact between the follower pin and the cam slot making it easier for Fusion 360 calculation engine to achieve the motion.  I have used the same trick on Rotate - Clamp cylinders modeled in Inventor. 

[TheCADWhisperer]

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@jhackney1972 wrote:

... you used the same slot we have been using. 

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If it were my project I would start be remodeling the slot from scratch.

I did not examine how @MADCannon0077 modeled the slot.

Ideally the contact patch would be along a line at any position of the cam.

as seen on the left - rather than on the right in image above.

It would then be interesting to see if Fusion will solve the Tangent along the entire slot.

[jeff_strater]

in @TheCADWhisperer 's "almost" design, you can see that the mechanism gets "stuck" here, on the selected face:

If I turn on zebra stripes for the outer body, it looks like it might be problematic:

Even with the fillet deleted, the follower gets stuck on that same face.

I did not have time to try to take it any farther

[MADCannon0077]

I just redid all the project following CadWhisperer method (using sheet metal) and it appears to be working so far (not very smooth but works). I also noticed that, as the angle of the slot is increased so is the jerkiness.

Attached is the project, I did it in a hurry so please forgive the mess.

Later on, I will compare both projects to see what went wrong with the other method (swipe with a twist) and repost my findings.

Thank you.