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Frank Hausman · Guest

We've tried SW2005 to lay out a fairly simple assembly, and animate it,
but it can't do it.

The assembly consists of:
- A base with a centered pivot joint.
- Two u-channel levers hinge on this joint, initially horizontal.
- Each lever terminates in a pivot, from which rises a telescoping
hydraulic cylinder.
- The tips of the two T.H. cylinders are joined at top by a short hinged
link. So this assembly has 5 linked "bars" (basically), with two "bars"
of variable length.

The lower bars swing up from a horizontal position to about 70 degrees.
The telescoping cylinders extend from the same length as the levers, to
3x that length.

SW2005 does not animate this assembly correctly. It "sticks" and
generates bizarre movements whenever we try to move anything, and
therefore cannot produce a useful animation of the mechanism rising from
a collapsed (nearly horizontal position) to fully-extended.

The telescoping cylinders are constrained "concentric" and are limited
in end travel.

We're seeking a solution to this problem in _some_ CAD package. We
resorted to animating it in Maya; probably Studio3D or Lightwave could
have worked.

But ultimately, we want to add the rest of the mechanical structure (of
which there's a LOT), and be able, however slowly, to simulate the whole
thing for collision detection under certain deflections of parts, and so on.

Sorry for the limited info and no image, but we will communicate
directly with folks who can seriously help us out.

Thanks for your time.

BoC · Guest

You are hitting a sore spot with me, though my "mechanisms" are all one
piece with molded flexible hinges. I can' use an actual curved hinge
segment which "goes backward" (its center axis flips to the other side
as the hinge bends the 'other way') and have the part move to those new
positions, as SolidWorks can't handle a radius whose center 'flips'
sides.

I have had to resort to multiple configurations and limit my range of
movement in each configuration to evaluate my part.

I can't guarantee there aren't some other workarounds which work better
or a dynamics Add-On to SolidWorks which might work better, but I just
haven't looked for them.

Bo

Frank Hausman · Guest

BoC wrote:

Bob · Guest

Hi Frank,
I'm no expert but I've found that it's sometimes important in deciding which
location (or link) of the linkage you are using to cause the motion or
change. Of course in real life it doesn't matter but it seems that, trying
to drive the movement of some parts of the linkage causes multiple solutions
and "flipping". Using other links or locations to drive the animation may
keep the animation stable.
Hope this helps
Bob, Toronto

"Frank Hausman" <lexein-arw@yahoo.com> wrote in message
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matt · Guest

Bo,

If you want help with this, I would be interested in taking a look at
it, or at least a simplified version of it with the links and all. Too
many open degrees of freedom will cause the kind of issues you're
talking about, so I would try to control things as much as possible,
using distance and angle mates to animate.

By the way, what are you using to animate in SW, Animator or Physical
Simulation?

Matt

BoC · Guest

Matt, I appreciate the offer. I can send you a quick model I did of a
one piece 4 bar plastic clamp from a competitor. I think SolidWorks
ought to be able to handle it in a simplified form, without getting
exotic and pricey addins. I am not currently using an animation
package, other than Animator.

I think a solution for link mechanisms is probably a 3rd party
application which can handle the design of mechanisms in some respects,
but I haven't had the time or interest to seach out such packages, as
they really don't handle what I sometimes do with plastics.

In the world of plastics, hinged & flexing designs of mine typically
runs into the issues of converting a flat piece of plastic into a
curved position, or maybe curved both ways as in a wide ranging hinge
use. In addition, a lot of plastic "hinges" wind up causing temporary
or permanent deformation which is definately non-linear, and all sorts
of 'over-center' snaps and inverted curved surfaces or beams are used.
Designing things that hinge, deform and spring and 'snap' overcenter is
a bit of trial and error right now.

I have not heard of an add-in or CAD package which can handle these and
suspect that it is so limited in market size that there is little
incentive for a software company to develop a product.

Frank Hausman · Guest

Bob wrote:

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