Motion Study on Mechanical Mechanism

[chillerfive]

Hey,

I'm looking to simulate the motion of a geared mechanism with some pin-slot components.

This example here is a fundamental problem in it's simplest form; the actual mechanism I'm trying to analyze includes pin-slots, levers, gears with lots of them mounted encyclical.

Back to the simplified problem at hand: I have the input gear K1 and want to to know the rotation of output gear K2. Thing is they're mounted eccentrically and connected via a pin and slot. Orange is the grounded arbor, green component is input gear K1 and opaque orange is output gear K2.

This should, given it's been designed properly, model a quasi sinusoidal output variation to mimick the moons mean sidereal rotation rate. The larger context here being the Antikythera Mechanism for which I am trying to design another 3D printable model.

Ideally I'd want a graph or a table of sorts.

Fusions Motion Study function is not adequate to simulate this for a couple reasons (AFAIK):

- only 100 time steps allowed per study (reducing accuracy to 3.6deg or requiring multiple partial studies..)

- no actual way to read the output angle other than to squint hard and note the *no decimal* joint angle of K2 in 3D space

- because adding joint K2 to the motion study but not driving it, does not update its angle in the small table on the righthand side.

I've tried with both options of a pin-slot joint as well as "all contacts enabled".

I feel like all the requirements are there but fusion doesn't take advantage of it or allows the user to extract that information apart from manually iterating the input angle +1deg and checking the output angle. I'd love for there to be a more complex tool that allows quick analysis/simulation of gear trains to aid in design. Specifically here I want to alter the eccentricity and pin radius on K2 to accurately simulate the moons 1st anomaly.

Current idea is to export the 3D model to blender and work in their rigid body simulation workspace as it allows an unlimited number of steps and every steps information is stored in a file (so in theory the output angle should be in there). Over the years I've come across some fantastic tricks on this forum so I'm hoping you can help me out or point me in the right direction, should I be missing something.

Thanks a ton in advance

[TheCADWhisperer]

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@chillerfive wrote:

I'm trying to analyze includes pin-slots, levers, gears with lots of them mounted encyclical.

I am trying to design another 3D printable model.

Ideally I'd want a graph or a table of sorts.

I've tried with both options of a pin-slot joint as well as "all contacts enabled".

Current idea is to export the 3D model to blender

Over the years I've come across some fantastic tricks on this forum so I'm hoping you can help me out or point me in the right direction, should I be missing something.

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I would use Autodesk Inventor Professional > Dynamic Simulation Environment for this type of mechanism analysis.

There are a plethora of Joints and associated functionality that do not exist in Fusion 360.

First thing I notice is that your pin is the same diameter as the slot...

This will cause friction and likely binding in your real world model.

[chillerfive]

Oh I always wondered why people use Autodesk Inventor instead of Fusion 360. I guess now I know why... I'll have to give that a shot. Thanks for the input.

As for the tolerances I'm aware, I simply created the very simplest possible file to isolate this particular part of the mechanism.

[davebYYPCU]

You can’t get that with 3 lines in a sketch?

Drive the source angle, read the driven angle.  Good for as much precision used in preferences.

Might help….

[chillerfive]

I mean technically yes...

But this is just basic trigonometry and manually entering the input angle in 5deg steps then noting the output angle is insanity. Much better suited to a simple python script. Especially considering I'm trying to tune the specific parameters to closely match the orbital parameters of real celestial bodies. Thing is that I wish to simulate a whole complex geartrain consisting of about 80 gears, discs, levers, cranks, pin-slots etc.

I've designed a large chunk of the mechanism already and purely based on motion links and contact sets fusion can accurately simulate the mechanism. It internally knows the angle and rate of each gears, it just doesn't allow you to see that or plot the motion. It would be extremely helpful for me to be able to check the turning rate of one or more gears and perhaps graph them (in a fashion very similar to the Motion Study UI) to see any cyclical variations etc...

As far as I understand that is exactly the point of a motion study from an engineering perspective.

[TheCADWhisperer · Accepted solution]

@chillerfive 

There are a plethora of Joint types (and associated functionality) in Autodesk Inventor Professional that does not exist in Fusion 360.

[chillerfive]

Oh thank you so much! This is exactly the kind of tool that I've been looking for. I never knew that Inventor could do that. I thought it was only commercial users, that were slow to adapt, that kept using Inventor.

I started learning Inventor last night but couldn't manage to produce a part from a sketch... turns out you assemblies are really only for assembling not for designing multiple parts at the same time. I'll need some time to wrap my head around the philosophy and limited toolset. Perhaps I can find a workflow of designing in fusion and then importing and validating in Inventor.

Again Thank You so much

[TheCADWhisperer]

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@chillerfive wrote:

I'll need some time to wrap my head around the philosophy and limited toolset.

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Limited toolset?

There are far far more design tools and functionality in Inventor than in Fusion 360.

https://www.youtube.com/playlist?list=PLp5izJt_zvN08mpY4UcYrzJV2N6QOLAIR

https://www.youtube.com/playlist?list=PLp5izJt_zvN0GnwEUFR1zE06nQvDAWxz2

[TheCADWhisperer]

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@chillerfive wrote:

...turns out you assemblies are really only for assembling not for designing multiple parts at the same time.

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@chillerfive 

What version of Inventor do you have? 2024?

You can model multibody solids and then Make Components to push to assembly exactly as you have done with your design in Fusion 360.

If you are running 2024 I can show you with your geometry the exact same steps that you used.

[TheCADWhisperer]

@chillerfive 

Did you figure out how to create Multi-body Solids and then Create Components in Inventor the same as you did in Fusion?