Pro-E Mechanism Dynamics connections

[Solarsrta]

I am familiar with 'Mechanism', but not 'Mechanism Dynamics'. I am having difficulty understanding how to apply the correct connections in order to get the correct joint reaction forces & moments. Pro-E help is "no help". I have attached a jpeg of a simple problem. Pro-E's suggestion of using a planer connection and a bearing connection does not work for me.

Thanks for any help you can provide.

 

[cadcamguy]

Here's a tip.. don't pick your joint axis from the screen... pick it from the model tree.

If you expand out the connections in the mechanism part of the model tree. It will break it down to say "rotation" or "translation" ..or both for a cylinder conection. What ever is applicable for that connection type.

Make's it much easier to ensure you are setting things up correctly. From the screen the pick... connection_1 axis_2
doesn't tell me if it's the trans or the rotate axis..guess one could commit it all to memory..not me

But from the tree it tell me that's the rotation part of the connect.. and a big plus to using the tree is when I want to apply a servo,spring,damper, or force to it then it's right click and it grabs the joint axis.....

much more easier !!

 

[Solarsrta]

Thanks, CADCAMGUY. If you saw my jpeg of my sample problem, here is what I think the correct reactions should be:

The rotating crank has a weight of 5.072 lb at a cg of 2.352 in from center. The rotation is 1,200 rpm, which is 7,200 degrees per second, or 125.66 rad/sec. This causes a centrifugal force of 487 lb. That will result in a radial force on joint A of 730 lb, and 243 lb on joint B. If I use a planer connection at A, and a bearing connection at B, all the 487 lb shows at A. With other connection I have tried, the 487 is divided between A & B --- neither is correct. It would seem to me that a planer connection would absorb all the moment.
According to what I understand, a 'measure' of system redundancies should read zero, and the constraints should be one in this case, but if I have a servo motor driving body 2, then the constraints should read zero -- is this correct?

What appears logical to me is what I show in the diagram -- Joint A needs to constrain x & y & z; Joint B needs to constrain x & y. However, that results in 2 redundancies (x & y). How do I get around this?

 

[cadcamguy]

Solarsrta,

Your losing me in the Dynamics. I've just noticed that setting things up for movement it is much much easier to make the picks from the Mech. Model Tree than it is off the screen mech. icons. At least to get the correct axis.

Afraid that's the extent of the tip I can give.

 

[Solarsrta]

Cadcamguy,

Thanks anyway for trying. It seems PTC has made this terribly difficult. No doubt if I could afford a new support agreement, PTC could clear this up.

 

[Solarsrta]

Has anyone ever seen an book or manual on "Mechanism Dynamics" written by an independent author? I have looked far & wide.

Solarsrta

 

[cadcamguy]

you may or may not get some more input here

http://www.mcadcentral.com/proe/forum/forum_topics.asp?FID=4

 

[cadcamguy]

You didn't post that 5-6 times over there did you?

Once would of been good.

 

[Solarsrta]

Dear Cadcamguy,

My apologies if I seem over zealous. No, I haven't cried on that site, but thanks for the tip -- I may. Most of Pro-E can be figured out by repeated trial & error. This time I am stuck. I do appreciate your help.

 

[cadcamguy]

No problem Solar.. it wouldn't be crying

There is more activity over there then here, It's I saw someone post the same question in multiple forums, that's the way to get zero response there. My bad for thinking it was you

I'd give it a shot

 

[brep]

While you are first learning/experimenting with MDX and MDO it can be a bit confusing understanding the different joint types and the associated constraints/DOFs. One tip in such cases is to use 6-DOF joints and then put servo motors (with position = 0) as constraints on only the specific axes you want to control. In this way you can achieve exactly the correct constraints with zero redundancies.

There's a page nio the online help that is worth printing out and sticking on your wall - it is titled "About Degrees of Freedom" and has a table of all the connection types (Bearing, cylindrical, ball, slider, etc, etc) and the associated DOFs.