Motion Analysis

Hi There,
When I was tring to do motion analysis with 4bar mechanism as given in
the folowwing link
http://www.me.uvic.ca/~mech410/Tut2001/ProMMotion.pdf
When I tried to creat link between one part and another using pin
connection, it forms perpendicular to the axis of the cylindrical
surfaces. Is there anything wrong with the points created along with
the part models? I exactly created as it is stated in the pdf. I tried
a lot but in vain. I Hope to get a solution for my problem here.

Is there a way to create connections and then import it to mechanica?
I tired that also. But it fails.

Thanks,
Shankar.

 

: Hi There,
: When I was tring to do motion analysis with 4bar mechanism as given in
: the folowwing link
: http://www.me.uvic.ca/~mech410/Tut2001/ProMMotion.pdf

The problem you are having, Shankar, is due to the tutorial being several revs out
of date.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.

 

: 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?
:
Previously, when I've run MM, it required you to install a C++ compiler to run.
This may be the problem you are having. However, it may be earlier in the process.
Did you also run an analysis, using the motor/motion definition and then save it?
If you had this already, I'm sure you could reuse it in MM and that would be the
best way to go. If there were a problem with the equations, it would show up in
running the analysis. This is where it should be test before going to MM.

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 - Did you install the C compiler? You do still need that.
<snip>
: 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.

 

: 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 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