Motion Analysis

"Shankar Venkateswaran" wrote in message news: snipped-for-privacy@posting.google.com... : Hi There, : When I was tring to do motion analysis with 4bar mechanism as given in : the folowwing link :

The problem you are having, Shankar, is due to the tutorial being several revs out of date. Since this tutorial was written, large chunks of Motion have been moved into Assembly 'Connections' and Mechanism Design. The Assembly module is used to create the pin and other type connections and MD is used to create 'motors', apply loads and define motion characteristics, then use all this information to run analyses which can include pairs or global interference checking. The results of the analysis, using you motion definition, can be played back and even captured as an mpeg file. You can reuse the connections/motors/loads/motion definitions in Mechanica Motion, but no longer create them there.

So, back to the beginning. You should start with figuring out how to assemble parts to make them moveable. Your first part will be, by default, the ground or fixed part, the only non-moving one. It can be assembled using 'Automatic' constraints. The two links will be assembled using pin type connections in the Assembly 'Connections' interface. You have to click the arrow next to 'Connections' to reveal the inputs. The pin connection requires that an axis in each part be selected and that some planes be available for a mate/align type constraint. In other words, the parts so assembled may rotate about an axis but have no 'end play', no side to side motion. When the connection is good, Pro/e tells you the definition is complete. And you should be able to click on the 'Move' tab and set the movement to 'rotate', click on the link and drag it around in a circle. The only one that is sort of complicated is the sliding part which will have two connections: a slider connection to the base and a pin connection to the second link.

When the connections are set up, you go to 'Applications>Mechanism' to start MD and give your mechanism life.

David Janes

Thanks for you responce David Janes.

After assembling with connections and motor i tried to run the mechanism in mechanica it say

"Compilation failed. Additional information may be available from outside of Pro/MECHANICA Motion by examining the engine's log file. Exit Pro/MECHANICA Motion and type 'mmwatch'.

Then I clicked ok after that. What I got was

"Failed while generating or compiling equations of motion for 'fourbar_linkage_mechanism_trial'. This may be a system or installation problem."

Is this because of Pro/Engineer Educational Edition?

what is mmwatch?

Thanks Shankar.

David Janes

Shankar - Did you install the C compiler? You do still need that.

mmwatch is one of the files where Mechanica puts error information when the analysis software (engine) fails.

I think I would create a single mass with a 6DOF joint to ground, turn on gravity and attempt to drop it. If you get the same error, it's not your mechanism.

Is Wildfire 2 Mechanica out anywhere yet? Next year is the end of Mechanica/Motion... right?

-D

Shankar Venkateswaran wrote:

: I think I would create a single mass with a 6DOF joint to ground, turn : on gravity and attempt to drop it. If you get the same error, it's not : your mechanism.

I don't know, man, this sounds dangerous and maybe, illegal: 6 degrees of freedom (rotate and translate about all Cartesian coordinates), in other words complete freedom of movement, then apply a gravity load and you want to drop it!?! Question:

1) Is there an up and down in cyberspace or maybe just a bias toward one coordinate over another; 2) Will it accelerate at 32fps squared to infinity; 3) What's to stop to it, break the fall; I don't know, I'd have to think about that! Couldn't you start crashing computers, bringing down whole networks and maybe create a black hole or something? Oh, yeah, and what *is* a joint with 6DOFs? I just can't picture it or make the connection. And double 'oh yeah' ~ if this requires any skill at all, remember, Shankar's just a beginner. Imagine if I'm a little scared by this, he's got to be petrified. (Okay, kids, now watch the instructor *very* carefully. And don't try this at home without adult supervison!)

And, Shankar, if you're using the educational version of Pro/e, it comes with up-to-date, PTC authored tutorials and practice parts. You need to get hold of that stuff, especially the course on Mechanism Design. The idea of giving instruction on something this complicated via email strains credulity. At very least, you need step by step instructions with pictures. It also might help to have an instructor.

David Janes

Hello, Actually I don't have admin rights for the systems I am working on. So I will have to forget about installing. I don't have access to the tutorial and was refused to help with that. Basically I work in UNIX platform. All those will have C++ by default I suppose. I am getting an error message when I run the four bar mechanism itself. I think the problem is with the assembly I guess. Why I say this because there are other mechanism which run successfully though I havn't done motion analysis on mechanica. I am still working on it. Thanks for the responce! Shankar.

"Shankar Venkateswaran" wrote in message news: snipped-for-privacy@posting.google.com... : Hello, : Actually I don't have admin rights for the systems I am working on. So : I will have to forget about installing. I don't have access to the : tutorial and was refused to help with that. Basically I work in UNIX : platform.

Where did I get the idea you were still in school using the educational version. Too bad you can't get to a school that has it. Worse, still, that your company would probably benefit from people knowing it but puts obstacles in the way of learning it.

: I think the problem is with the assembly I guess. Why I say this because there are : other mechanism which run successfully

How are you running the mechanism? With Mechanism Design? What rev are you on, I don't think that's ever come up and whatever we say, however you describe the problem is very version dependent. Since about rev 20 or 2000i when PTC introduced MD, they've been moving Mechanica Motion code and functionality into Pro/e MD. And, as meld_b pointed out, MM is going away at some point. So what I'm saying is forget MM and concentrate on MD, it's the future and it's presently the place (since about i-squared) to debug and investigate the problem you are having, especially if you suspect the problem is in the assembly. Or, it could easily be in a motion definition, values in a formula describing movement characteristics that are impossible. The place to test this is in MD. In fact, one quick way to see if you've assembled everything correctly is to go into MD (Applications>Mechanism), find the Drag Component function (where you can create snapshots and define intial conditions), click on the sliding component and drag it. Sometimes this works better with 'Drag point' than with 'Drag body'. If it moves at all, the problem will likely be in a drive motor. If it won't, then you have to back track through the assembly connections to make sure nothing is locked with improper constraints and to make sure a body isn't locked altogether. One final hint: the points in those parts should not be used for assembly, as a general rule. They were more commonly used earlier in place of current pin, bearing and ball joint type connections. They've been replaced and using them may only confuse things.

David Janes

Ah- you're right... I've been doing this so long I don't have any fear of much. The computer will not crash due to something accelerating off quickly. Importing the wrong sort of IGES file with Independent Mechanica might take at least Mechanica down.

1) When you put in the gravity load you define both direction and magnitude as in x,y,z = 0,-9806,0 mm/sec^2 respectively. 2) Yes, it accelerates off quickly. As soon as it flys off the screen you know it works. You can either hit a reset or let it time out, either way it doesn't take long and doesn't hurt anything. You actually don't need to run a Motion analysis, and could do just an Assembly - you get the same errors. 3) OK, use a slider pointed down. I think the 6DOF works too. There is no difference between a 6DOF with the right axes set to zero (via a driver) and the other types of joints. Sometimes this joint is the only way to go. 4) I don't really remember trying free compilers, but all our years on Sun UNIX boxes we always bought the compiler. For the few hundred we paid it seems like such a deal now that Microsoft makes us buy one at $100 for EVERY Windows user. Ah, but with the new software (MDO?) you don't need a compiler

And to David, I've read some of your long and helpful postings here. I'm not sure that anything I said was any more advanced than some of your novelets 8-) I'm still trying to wrap my head around how having a mass accelerating off the screen is a strain on one's credulity.

-D

David Janes wrote: