Creo parametric 5: some tips on mechanism/gear

[meccanico]

Hello,
I'm starting to use the mechanisms with Creo and would like to play a kinematics with a bevel gear (or conical pair ,  I do not know the translation of "coppia conica" in italian),   similar to the one in the video I've linked (they're only 3mb). 

The assembly is very simple, it is composed of:

A)a fixed body (the vertical shaft to which the first gear is fixed , they do not rotate and does not move)

B) the moving bodies: the horizontal shaft (motor), which being free to turn both on its axis and on the vertical one, will turn the box into  which it is inserted (with tho radial spherical bearings ).

I should also understand how to set the ratio so that 90 degrees of rotation on the vertical axis correspond to 90 degrees of rotation of the horizontal shaft axis, in practice 1: 1.

Reading the guide I understand that to use the mechanisms in Creo Parametric  you must use the constraints defined by the user instead of the automatic contraints , my problem is to understand where to put them.

For example, I would have left like this:
1) the vertical shaft placed as default / fixed
2) Its ring is  fixed on the shaft with automatic constraint , without any degree of freedom.
3) horizontal shaft with pin constraint , to allow rotation on its axis,  inside the box
4) pin contrant also for the box, free to rotate around the vertical axis (or should I to constraint it   to the horizontal shaft by matching the axes of the box holes with the orizontal shaft axis, plus the corresponding horizontal planes?)
Then I would go into applications> mechanism and define a bevel gear (translate conical pair gear) . However, here it allows me to select only axes that can rotate, so that of the horizontal shaft and that of the box (if constrained with pin)
Basically, how do I tell Creo that one of the two gears is fixed ( that at the base of the box) while the other turning around moves on a circle of radius r = radius conical gear?

p.s.I just have to set the movement just to do a kinematic, not dynamic, analysis

[gfraulini]

Hi,
the video you posted is awaiting approval yet, so I can't understand exactly all you've written.
Could you attach the assembly?

In the meantime I want to give you some tips on mechanism.
Here one have two kind on constranits: the "standard" and the "mechanism" ones.
The firsts are what program suggest you when you add new components to the assembly (mate, alling, tangent, fix, defoult, etc...); the seconds you have to switch to pin, planar, slot, bearing, etc...
Linking compononents with the standard ones mean to create a body, a set of components rigidly linked.
The second ones serve to link different bodies together.
Each body has 6 dof (degree of freedom) in the space; you have to impose mechanism constraints in order to remove dofs.
Eg: a simple bshaft rotating around its axis.
A shaft is 1 body with 1 component and 6 dofs where you have to give it only 1 dof: the rotation on its axis. So you have to remove 5 dofs; a simple pin constrain is what you're going to need.

Bye

[meccanico]

Hello Gfraulini, thanks for your reply and for the clarity of your  explanation ,I knew more or less what you told me but it was a useful confirmation because the movement is a topic that during the PTC course in which I participated, we have not talked about this topic.

I am attaching the file with the assembly. I have gotten this result by chance, after numerous attempts and  before reading your answer. the movement give an idea of what I would like to get but it is not correct because it is not 1: 1, and even the  constraints I do not think are applied in the right way,The same for the gear
I attach the files to better clarify the moving parts and how this  assembly is composed.

bye

[gfraulini]

I will return in office on monday and I'll get a look at your assembly.
But, if you want send us some pics, we can give you other suggestions.

Remember that you have to respect the rules I've written only for dynamic and static analysies, where forces enter in play.

If you want to do position or kinematic analysies you can bypass those rules.

I give you an example: a door. A door is a body that can only rotate around an axis. So it has 1 dof. You can to assemble the door directly in an assembly or onto another part (a frame for example). The doors have two or three pins in the reality, but, in terms of multi-body analysies, there are redundancies. In fact for a correct multi-body analysis you have to constrain the door with a constrain that limits 5 dofs; the simplest thing is to use the pin constraint (there are also other methods to obtain 5 degees of constraint, but let's limit us to this one).
If you run position/kinametic analysis, you can assemble the door also with three pins; but if you run the other ones that contemplate forces (always with the three pins) the results will be incorrect.

[meccanico]

this is useful information, I would have put two / three pins on the door, now I know that for the dynamic simulation it is more correct to put one.

sweetpeahub I will meditate on what you wrote, then I will update the post the post

thanks to both of you!

I am attaching a scheme made on the fly

[SweetPeasHub]

Yes, gfraulini found your simple issue with the gear ratio.  You should mark his as an answer so he gets credit.  I also attached updated model per my suggestion.  This is working with gearbox as the ground body in a sub-assembly until attaching the output to create the moving gearbox.  Your way is fine, but sometimes easier to model, evaluate, and understand the gearbox while it is stationary.  I will explain in case you do not have CREO 5.

Separate GearBox method

[meccanico]

hello, I was off-site today and I could not try, I'll test this test tomorrow.I would like to thank you both because your help is precious.
The model that I attached is very simplified compared to the real one, here I tried to put the essential, on the simplified model the movement is correct, so I assume it will also be in the real one. The information from sweetpeahub will become very useful to better organize the real model, because really how it is organized now is very difficult to understand, yours was the answer to the other question I did,  so the credit would go 50% to each, you decide to whom I must put the credit, based on who of you can be more useful

[meccanico]

I initially chose conical gear ( because the gears I'm using are conical) but even setting ratio 1: 1 I had a reduction / multiplication ratio.

Olnly after, choosing generic gear and leaving 1: 1 the result is correct. that's .Iy is also for what I did not understand how to solve

[gfraulini]

I'm honest, I've never used gear connections outside the generic-user defined one.
And this because I'm, almost always, interested on studying the system kinematic/dynamic and not the support forces.
So, if I define a gear, I'm interested only on setting the ratio. I've never use bevel gear, and aspecially bevel gear with pitch and diameter ratio definition; but now I see that in this manner you can't specify the pitch circle diameter of the second gear...Maybe it's a bug? But I have the same behaviour both on Creo 3 and 5...

[SweetPeasHub]

Not a bug, but it would be nice if the icon location followed the gear2 pitch circle rather than the other way around.

For the case of Bevel gear the "Icon location" is used to calculate gear geometry.

case "pitch circle diameter" icon location defines GEAR2 pitch circle and  Bevel Angle

case "user defined" icon location defines GEAR1, GEAR2 pitch circle, and Bevel Angle

The distance from the GEAR1 "icon location" to the GEAR2 axis sets Gear2 pitch circle.

The angle between both gear axis along with gear ratio sets bevel angle.

[meccanico]

I follow you with interest.

One last question, how do I reverse the direction of rotation of one of the two axes of the  gear motion? re-doing the assembly , it happened to me that the the orizonltal shaft  rotates  on its axis in the opposite direction to the one with which it should rotate, compared to the box .  It is very evident because gear attached to to the horizontal shaft  ,rotates with a direction opposite to its direction of advancement

[SweetPeasHub]

Flip Direction

[meccanico]

perfect! thank you very much

[gfraulini · Accepted solution]

I've seen your assembly. It's correct. If you want 1:1 transmission ratio you can do this (see pic attached).
In addition you have 0 redundancies and 0 dof (zero because the one dof of mechanism is taken by the motor).

Bye

[SweetPeasHub]

i have not looked at your model but i have done the “stationary” gear thing before. i am not in my office so not able to look it up at the moment. my memory is that you should make a subassembly where the shaft rotates on a pin joint and define a gear connection. then assemble the subassembly to your “ground body” assembly with the moving shaft fixed in position. Basically this is how you make a gearbox rotate rather than the output shaft rotate. There are other ways to do this of course.

in short. make a gearbox subassembly with rotating output shaft. then rather than assembling the gearbox housing to ground assemble the output shaft to ground.