Complex Assembly Animation Issue

[Anonymous]

Hello!

I have an issue with the animation feature of Fusion 360.

I created a beam which rotates on a custom axis and another which rotates on the opposite end of the part.  The second beam does not rotate along the second axis.

As you can see, the second rotating beam does not rotate in a circular pattern in line with the first beam.

Any suggestions?

http://a360.co/1S7GIAL

[TrippyLighting]

Looking at you file I believe that this is hard to do with the current animation module.

It does not honor joints and as such I find it somewhat defeats it's own purpose.

[Anonymous]

Thanks for the reply.

Is there a better way to do this without using the Animate tool?

[TrippyLighting]

Well, that depends on what you are actually trying to achieve.

If you just want to visualize that motion then the animation workspace would theoratically be the right way to do it.

If you want to create a functional assembly you need to use the joints from the Assemble menu. 

[Anonymous]

Okay. I'll tinker around with it for a couple of days and get back to you.

Thanks again for the guidance.

-D

[O.Tan]

I've tried using joints for your model and it seems that this is one of the limitation of the current joint as right now Joint motion with Motion Links/Motion Study only works well if the joints is at a linear rate, to get the animation you wanted, Fusion will first need to be able to do non-linear rate motions.

I tried some workarounds but I can't get exactly what you wanted, there's always some hiccups along the way.

Perhaps we need an AD employee who's involve with Joints to chime in here

[O.Tan]

This is what I'm able to achieve and highlighting the issue, if I were to increase enable the 2 more rotational constraint, it'll break the model

And attached is the file you gave with the adjustments made

[TrippyLighting]

If the animation module would simply honor joints that would not be a problem.

[georgehudetz]

Hello, thanks for posting!

This is an interesting motion study you have here.  Can you describe a little more what the specifics of the motion are, and what you are looking to learn?

I can tell the short arms go through 360 degress of rotation - is it intended to be constant angular velocity, or doe the angular veloctity change over time?

The longer arms seem to go through 180 degrees of motion, but it looks like you want the beginning & end of the motion to be defined by contacts, but when there is no contact you'd like something to drive that joint?  Again, would the angular velocity be constant duing that motion range?  Or is there some other way you'd like to decribe, or impose, this motion?

Thanks,

George

[Anonymous]

George-

Thanks!

The static arm is Layer 1, the short arms are Layer 2, and the long arms are Layer 3. The constant angular velocity shouldn't change for any layer. The representation of the change is either my fault as an animator or a feature which isn't present in the program. You're correct in your analysis of L3 rotation. Each complete rotation of the L2 is one half of L3 rotation.

I'm interested to learn whether or not I can have axial rotation along a circular path. My animation allows for a conceptualization of the rotation of the layers but the clipping is inaccurate and distracting. There should always be contact between the L3 bars.

Did this explain my issue?

-David

[georgehudetz]

Hi David.  Yes, that does help thank you.

I was able to make a design similar to yours, but I used revolute joints at all the pins.  (http://a360.co/1ZIKvKr)

What is interesting to me is that I don't think you can get constant relative angular velocity between L2 & L3 if you want the two L3 arms to always be in contact - I think the contact will force a non-constant relationship between the two arms from an angular velocity standpoint.  I could be wrong but looking at the motion study I made using constant angular velocity on both sets of arms, the L3 arms intersect with one another during certain parts of the range of motion.

To keep the two arms in contact with one another during the movement you are looking for, we'd need some kind of contact/slider/follower joint in Fusion.  I may be wrong - and if somebody else has an idea hopefully they will speak up - but I think you'd need such a feature before you can properly visualize this motion.

I also assume you want to capture an animation of this movement.  As was stated earlier in the thread, the Animation workspace does not recognize joints, nor does the Motion Study dialog allow you to record the movement into a shareable video.  Both would be nice additions to Fusion, but I'd wager that the addition of a Record button to the Motion Studies dialog would be more straightforward.

I know this isn't the answer you were hoping for, but both suggestions (contact/slider/follower joint, and the ability to record the motion in a Motion Study and/or making Animation recognize Joints & Motion Studies) would be good additions to the IdeaStation, or, if they are already there, you could add your vote.

I'm happy to continue to correspond with you on this task, as I am working with a team that, eventually, may be looking into issues like this in more detail.  Again, not in the immediate future, but tasks like these are on our radar.

Thanks again, and good luck!

[Anonymous]

George and O. Tan-

I made a mistake!  The rotational speed L3 is NOT linear.  If you watch my animation, you can see that it does not have constant speed.  At 1s, L3 is one angle and at 2s L3 has a larger change/second.  The video O. Tan uploaded shows that a constraint along the ends of the L3 arms would put it out of sync with the L2 arms.  The file George uploaded has a constant rotational L3 speed and the parts clip.

I suppose the next logical step would be to add a feature which allows for non-linear acceleration of joint movement.  Another possibility is to add a pin slot joint to compensate for the clipping and desynchronization.  The only issue I see with that is that the slot itself would have to be a seperate part to avoid further clipping.

What do you think?

-David

[O.Tan]

Yes, that was what I wanted to point out, besides joints not having the ability to follow path (hence can't animate, chains, timing belts and related to it), it also will have issues when non-linear acceleration motions like in your case has shown.

TBH, I don't think the pin slot joint will work as well cause the issue here is as you mentioned, the angle accelerates at certain point and then decelerates for it to match with the other joint and then this process repeats one more time until 360deg.

[georgehudetz]

Agreed about the need for non-linear motion profiles, as well as the ability to follow sketched profiles.

As for the slot, perhaps a combination of slots would give the motion that is needed? I know one can create specific rigid-body motions through a combination of slots, but it's unclear to me if we could get what we are looking for in this particular case.

[Anonymous]

I think the issue is the same. The pin in the slot as well as the rotation of the slot would be non-linear in speed.

Sent from my iPhone

[Anonymous]

Hmm. I see what you mean. I played around with the idea of a ring gear in the shape of L3 (unfortunately on paper and not in the software) and the issue still presents itself as the gears maintain constant speed.

I'm playing around with another idea for a more complex gear system, but without an idea of speed per rad of L3, any kind of static gear reduction is hard to calculate with chipping tolerances in mind.

I'm wondering if a spring in a a lot would work as well.

Any suggestions?

Sent from my iPhone

[O.Tan]

Hmm, care to clarify what you mean by spring in a lot would work?

Right now there's no official tool to animate springs

[Anonymous]

Excuse me. A slot*

[Anonymous]

George-

If we assume the different arms are driven mechanically through gearing, a good definition of the issue is that non-circular gears don't work; in that L3 would be driven by a ring gear, which contains elliptical gears, and is not circular in nature.

Thanks for your help.  I know we got a little sidetracked from the original problem - but I'm glad we did!

-David