Mechanism Joints, movement not working

[pavlos_kakouris]

Hi everyone,

First time poster here. I am working on a mechanism for a university project and I am having trouble modelling the joints needed in order to achieve the movement I want. An example of the mechanism can be seen in this video:
https://www.youtube.com/watch?v=191Wmn9h-GI
And an example of the movement I want my model to be able to achieve can be seen in this video:
https://www.youtube.com/watch?v=8OuYhhAxe8I

For clarity, see the following image of the model (which you can find attached):

The mechanism consists of 5 bearing positions, marked with 1 on the image, which I have modeled as revolute joints using as-built joints. Position marked with 2 is direct rotation actuated by the motor which I have again modeled as a revolute joint in Fusion. What I want to achieve is to be able to grab the top surface of the pink component and rotate it at the same time around x and z-axes to imitate the movement of the mechanism and have the joints (and limbs) rotate automatically and find the position that they need to be based on that movement. I have grounded the pink and red components. After modelling all the joints, the model locks up and I can only rotate around the x-axis. I am not sure if I am doing something wrong and restricting the rotation around the z-axis or the simultaneous movement of the limbs based on the pink component's movement is too complicated for Fusion to do on its own.

Thank you in advance! 

[TheCADWhisperer]

@pavlos_kakouris 

Are there any unresolved issues highlighted in your Timeline?

Are all of your sketches fully defined?

Can you ask your instructor to join this discussion?

I haven't dug deep into the mechanism, but on cursory examination it appears to me that the axis between Intermediate Limb and Ground is limited to a single rotational DoF - preventing the motor axis from turning.  I have to run at this moment and will have to come back later...

[pavlos_kakouris]

Thank you for replying! No unresolved issues in the timeline and all sketches fully defined. My instructor can't join.
When modelling each limb rotations separately, so Limb 1-Mounting bracket and Limb 2-Intermediate Limb-Mounting racket therotations around both axes work fine, it is when I connect the two 'systems' that the model locks.

[TheCADWhisperer]

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@pavlos_kakouris wrote:
 No unresolved issues in the timeline 

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What are these yellow highlights?

Does Ctrl b (CMD b) return any issues?

[TheCADWhisperer]

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@pavlos_kakouris wrote:
.... and all sketches fully defined. My instructor can't join.

I haven't dug deeply, but I am seeing different observations than what you are reporting...

[jhackney1972]

I have freed up your motions except for the Motor revolve joint since it directly interferes with the joint on the Ground component.  Since the Ground component is fixed, I believe the motor joint is impossible.  As mentioned, you have a lot of unresolved issues in your timeline.  Model is attached.

[pavlos_kakouris]

Apologies, the unresolved issues in the model I uploaded are because it's a simplified model and I copy pasted the components from the actual model. I have attached a model with no issues and I am confident that the differences of the simplified model to the actual is not the problem since they're just some design details which I am not using in the joints formulation.

There are still some not fully defined sketches but I thought it was just good engineering practice, not a necessity that might interfere with the model. If it is and you think it will help solve the problem, then I will provide a model with fully defined sketches.

[pavlos_kakouris]

Hi John, thank you for your model. Issues aside, is it your opinion that the simultaneous movement of all three limbs (limb 1, limb 2 and intermediate limb) based on the thruster movement cannot be modeled in Fusion?
I am confident that that the actual application of this kind of mechanism is how I am describing it and can also be seen better in this video:
https://www.youtube.com/watch?v=OnD7vbq18lg
Where with varying pointing direction of the central bracket, the rotation of all limbs is required and this is what I am trying to model. Thank you!

[jhackney1972]

I looked at the video, such as it is very hard to see, and I personally believe you have misinterpreted some connections and motions.  Fusion 360 is capable of this movement, maybe not automatically animating it, but capable.  Looking at your model, if you rotate the motor in your mind, and follow up the chain you will see that there is a direct violation of the motion at the grounded component which is a simple rotation.  There may be limited motion at different points of rotation of the other components but you will have a lot of interference.  Fusion 360 will have a hard time determining which motion is allowed at any one time.  A Fusion Motion study, which is difficult to create and run will be required to synchronize the motion.

[davebYYPCU]

All things equal, Fusion will do it.  Not software but, is data related.

Revolve - locking the file - triple check alignments.

Because alignments must be precise, yellow icons (explained), or not fully defined sketches, can be a source of the alignment problem.

As Built Joints and parameter changes do not mix.

I don’t have access to files until tomorrow my time.

Your graphic picture, is not same as John’s picture.

you say pink handle is grounded, that will cause the problem, and is not required in the joint system.  (Not present in last movie) Your pink handle should collide with lime green arm in some positions.  For johns picture, the blue arm is turned 90 degrees from rest position.

Might help.....

[TheCADWhisperer]

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@pavlos_kakouris wrote:

Apologies, the unresolved issues in the model I uploaded are because…

There are still some not fully defined sketches but I thought it was just good engineering practice…

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The unresolved Timeline issues and unconstrained sketches might not have anything to do with the motion problem, but when I ask a student (I taught for nearly 30 yrs) specifically about this and they tell me “doesn’t exist” I start to worry how many other “good engineering practices” they ignored and how deep I will have to dig to find the root cause.  This is why we have children cheering as they watch their super-heavy lift rocket, largest ever built, destroy itself along with launch pad. Some issues are hard to discover, but if we just ignore the obvious…

[pavlos_kakouris]

Refering to this video:
https://www.youtube.com/watch?v=8OuYhhAxe8I

Red in the video is light orange in the image of my original post (Limb 1 in model), blue in the video is Turquoise in the image (Intermediate Limb in model), green in the video is lime in the image (Limb 2 in model). I can't see what I might be misinterpreting from this video (and the other videos of real life applications), in order to achieve the same motion. Especially after 0:09 where the blue limb is rotated according to the rotation of the red limb and therefore the rotation of the motor, without affecting and interfering with the rotation of the green limb.
Any suggestions as to what I might be misinterpreting much appreciated.

[jhackney1972]

I can now see that you DID NOT misinterpret the YouTube video in your mechanism.  In the attached video I loosened up two of the joints using two cylindrical joints.  I then drive the motor my hand which show linear motion between the blue yoke and the fixed red mount.  I think this shows an incorrect length on one of the grey members.

[jhackney1972 · Accepted solution]

If you place Axis between your main members, it will reveal that you also have some alignment problems which could be related to dimensions issue mentioned in my last post.  Model attached.

[davebYYPCU · Accepted solution]

The motor - not close enough.

Might help.....

[pavlos_kakouris]

@jhackney1972 @davebYYPCU Thank you both for your contributions and spending the time. The issue was indeed the misalignment of the axes. Thanks again!