topic Re: JOINTS - After 18 months, I still hate joints. in Fusion Design, Validate & Document Forum

JOINTS - After 18 months, I still hate joints.

engineeringNCMXB — Sat, 02 Mar 2019 02:39:06 GMT

20+ year Solidworks user that partially switched to Fusion 360 about 18 months ago.

I am doing a quick motion study on a mechanism. It is a pin captive in two slots that are rotated about 90 degrees relative to each other.

Here is a pic....
.

The idea is that as the two arms with slots move, the pin in the center is translated. Essentially, the pin/slot relationship needs to happen in both slots while the part with the pin maintains a fixed distance from the base part and the edges should stay parallel.

It took me a few hours to learn Solidworks mates 20 years ago [the equivalent of joints]. Here I am a year and a half later with Fusion 360 and still regularly run into unnecessary challenges or a limitation with joints. Perhaps I am super stuck in my Solidworks ways.

Public link to the model as they are now. If anyone is able to provide some clues - I am all ears.
https://a360.co/2Enat2M

Re: JOINTS - After 18 months, I still hate joints.

davebYYPCU — Sat, 02 Mar 2019 04:24:45 GMT

Reasonably simple,

As built Pin Slots on the pin and each slot, (2)

Slider on both plates.

Might help...

Re: JOINTS - After 18 months, I still hate joints.

engineeringNCMXB — Sat, 02 Mar 2019 04:48:23 GMT

Thank you for taking the time to reply.
Perhaps it is reasonably simple.....but I have only received errors and an immovable model. Your suggestion is where I started.

I just want a pin to be tangent to two edges of two separate parts. I also need the two large flat parts to maintain a specified distance. The edges of the two plates need to remain parallel.

So far, I have not managed to get past the first step in a multiple step process. I am more than willing to admit that I am not at a genius level with Fusion 360, but this seems so fundamental and I was doing similar mates in Solidworks 20 years ago after a few hours of self-instruction.

Re: JOINTS - After 18 months, I still hate joints.

davebYYPCU — Sat, 02 Mar 2019 05:18:43 GMT

Attach your file, I will check what does and doesn't work, but I can not access the file with the link.

Re: JOINTS - After 18 months, I still hate joints.

engineeringNCMXB — Sat, 02 Mar 2019 05:25:53 GMT

I am not sure how to attach a file - did a quick check to make sure the project was sharable.

Shared Link

Re: JOINTS - After 18 months, I still hate joints.

davebYYPCU — Sat, 02 Mar 2019 05:33:27 GMT

File > Export save to hard drive, then attach in the attachments box, just below the message window.

I can open and see the file in A360, but not download it from there.

The plate with the pin is not centred in the pic, and the distance the top plate is allowed to move would be handy.

Re: JOINTS - After 18 months, I still hate joints.

engineeringNCMXB — Sat, 02 Mar 2019 05:35:52 GMT

I see the attach file button now.....

Here it is.

Re: JOINTS - After 18 months, I still hate joints.

engineeringNCMXB — Sat, 02 Mar 2019 06:02:52 GMT

Thank you for taking a look.

I will continue to fiddle with this hoping I get lucky. At this point, I am guessing it is beyond the capability of joints on their own so I am looking at tricking it somehow.

Re: JOINTS - After 18 months, I still hate joints.

davebYYPCU — Sat, 02 Mar 2019 06:49:28 GMT

Thank you, got the file, it's not working for me so far, and I am getting errors of a reference lost type.

Will update when I have something more worked out.

Re: JOINTS - After 18 months, I still hate joints.

davebYYPCU — Sat, 02 Mar 2019 07:27:10 GMT

Working, with errors, that I don't know what they mean.

what I did, deleted the grounding and all the joints, capture positions.

The Base plate, made into a component, grounded.

Create As Built Slider with Plate and pin, with vertical direction.

Create a sketch in the pin component, on the common face of the swing arms, project the pin, then add a Joint Origin on that centre point.

Create Pin Slot Joint, with the Pin being moved, I selected the common face, centre point of the lower end of the slot,

the slide direction altered to Custom, and the edge of the slot selected.

Drag the pin, all works as expected, but still has 2 yellow icons,

@jeff_strater any idea what the error means?

Might help...

Re: JOINTS - After 18 months, I still hate joints.

TrippyLighting — Sat, 02 Mar 2019 11:49:26 GMT

Ultimately this is unlikely to be a problem with the pu-slot joint although that one is a bit more fiddle that any o hue other joints.
This is a problem of assembly structure.

Body1 belongs to the base component. However the base component has other components with their own bodies at the same structural level with Body1. That almost always leads to problems.

If you have an assembly it should only contain other components, but no bodies.

I'll see if I can figure this out and then create a screencast.

Re: JOINTS - After 18 months, I still hate joints.

TrippyLighting — Sat, 02 Mar 2019 13:13:33 GMT

@davebYYPCU @engineeringNCMXB I think that the pin-slot joint turns yellow is a bug in the joint.

It works fine with an as-built joint but not with a regular joint. I will report it!

Here's the link to the bug report.

Re: JOINTS - After 18 months, I still hate joints.

Anonymous — Sat, 02 Mar 2019 13:56:34 GMT

I have a question about your design intent. You said the edges need to remain parallel. Do you mean the edges of the base and the moving plate? Setting aside any limitations of Fusion 360, this requirement is mechanically impossible using only a single pin as there is nothing to prevent the pin\plate from rotating.

Kelly

Re: JOINTS - After 18 months, I still hate joints.

engineeringNCMXB — Sat, 02 Mar 2019 18:36:27 GMT

That is a good question...
In the finished arrangement, there will be an additional mechanism that keeps the moving plate reasonably parallel. It is not depicted here and the joint is effectively a 'magic force' holding it parallel with the expectation that additional mechanics are needed to make that happen in reality.

Re: JOINTS - After 18 months, I still hate joints.

engineeringNCMXB — Sat, 02 Mar 2019 18:38:08 GMT

I am thrilled to see the responses when I woke up this morning! For the moment, I think I will arrange the assembly a bit different to see if that gets me any further.

Re: JOINTS - After 18 months, I still hate joints.

engineeringNCMXB — Sat, 02 Mar 2019 19:10:23 GMT

@davebYYPCU You got much further than I have.

The limitation is that the center pin is defined as a SLIDER early on, which restricts it to a single axis. The end goal is to allow the pin to move on two axis - X/Y within the boundary of the bore on the bottom plate. The arms would be individually manipulated to get the desired X/Y position of the center pin.

Here are some examples that I manually arranged. You can see that the arms are not symmetric and the pin can be placed at any XY position within the bounds of the bore that it is in.

Re: JOINTS - After 18 months, I still hate joints.

davebYYPCU — Sat, 02 Mar 2019 19:54:58 GMT

What you asked for was doable, I disregarded the time lost chasing the error when it was working, anyway,

Aah, you did not say that you wanted that new criterior included.

I have never used a planar Joint, but I can only assume the Planar can replace the Slider, but have no experience on how it’s Joint limits would work, if a radial distance is available, or not.

a contact set (they hog performance) for the pin in a hole, comes to mind.

Might help to add the features of the pin alignment soon,

Re: JOINTS - After 18 months, I still hate joints.

engineeringNCMXB — Sat, 02 Mar 2019 20:08:58 GMT

Thanks again for looking....I am trying to refine the question/criteria as best I can.
I did make a screencast to best show the intended outcome - but by using Solidworks. It took me about 5 minutes to model and mate the exact same thing [successfully] in Solidworks.

Re: JOINTS - After 18 months, I still hate joints.

davebYYPCU — Sat, 02 Mar 2019 20:17:03 GMT

I did not intend to be critical of you, just an off the cuff remark, (similar to - now you tell me.)

But will say that if it was mentioned earlier, I missed it.

Re: JOINTS - After 18 months, I still hate joints.

engineeringNCMXB — Sat, 02 Mar 2019 20:32:12 GMT

I did not take your comment in any negative way - no problem.
Sometimes it is hard for me to articulate a question that is actually a bunch of questions rolled into one.

As a side note:
Joints are great in certain circumstances and just horrifying in other circumstances. The concept of 'MATES' in Solidworks may be a few more mouse clicks sometimes - but ultimately flexible in defining motion and assembly restrictions. If F360 implemented both options - it would be killer. For a while, I have just been waiting for the concept of 'joints' to click in my Solidworks brain - but they have not. At this point, I simply see joints as a bad idea or at a minimum half baked implementation. Perhaps for users that have only used Fusion 360 this is not obvious - but Solidworks figured this out decades ago.