Real world v SolidWorks 1

[charliedurrant]

Bare with me everyone, I know I'm as king a lot of questions....(and thanks to all that have taken the time to answer so far)

Background - I am new to modelling / CAD / drawing etc. I am transferring some old autocad files into a 3d model. The files represent a replica of an old swing frame - nothing smart, just some tubes, hinges and an apex joint.

The whole lot is at

http://www.wilverley.com/Assembly.zip

and the the e-Drawings file is at

http://www.wilverley.com/Assembly.htm

I have two problems:

1) I have a folding brace (like the ones you get on baby push chairs) which connects to tubes which are fixed at one end to a joint. The brace locks the two tubes (legs) and when locked out fixes the distance of the two legs.

The problem is in 'the real world' the brace has an element of flex around the set screws where it is fixed and both faces of the stay that connect to the legs sit flush against the legs. Solidworks wont let me create a coincident mate as this would mean the other components would have to twist. It makes sense ofcourse but in the real world I am not forced to have a 5mm gap..... What should I do to emulate real life.

2) Before the legs were linked together by the brace they had movement in two ways

a - rotation about the set screw where they are fixed to the apex joint hinge.
b - where they are attached to the apex joint, the hinge they are attached to had perperdicular rotation about another set screw.

Once the two legs were linked by the stay I lost movement 'a' even if both legs were selected together.

Thats the end of my questions ! I can't find anything in the help files or on web searches etc.


Charles

 

[bvanhiel]

Ask yourself: am I trying to create a motion simulation or am I just trying to get drawings done. You may be doing a lot of work that will have no benefit.

That said, here's some ways to do it:
1) Create points to constrain joints. This will allow you to have virtual ball joints that will help you keep from creating an overconstrained condition.
2) Create configurations of parts in bent positions. If you have a part that needs to be flexed. Create a configuration of the flexed part for use in the assembly.

-b

 

[charliedurrant]

b,

1) I'll take a look at constaint points - I have not come across them before - only mates in an assembly (as described in the help)

2) I do see what you mean.....the drawings have two purposes a) for construction and b) detailed instructions on how to errect the frame. It would therefore be very nice to freely manipulate the frame as it can be in real life. Are you saying I can't match the real world motion in solidworks.....drat, if thats the case.

Charles

 

[ShaggyPE]

Concerning your issue with the 5mm gap. Make a plane on one of the parts (we'll call it part1), offset 5mm. Mate this plane in your assembly coincident to the face (on part2) that you intended to mate the original face (from part1).

-Shaggy

 

[bvanhiel]

Charles,

You may be able to match the motion, but it's probably more work than it's worth. Solidworks is not realtime FEA, so it doesn't know how to deal with parts that deform unless you are explicit in their definition. One way to do this (which I use for animations) is to use equations or assembly references to define parts that move or flex in response to the assembly. Not worth the time unless you have a very specific need.

-b

 

[charliedurrant]

b,

I can definately say that equations would put be over the edge ( I doubt my maths and grey cells would cope ). I'm still unclear as to why the legs are locked in position.

Why is it that once the stay is in place both legs seem to forget that they can move - they did before. The stay just locks then into the same plane it shouldn't prevent them from being able to move with each other?

Charles

 

[charliedurrant]

Shaggy,

I see what you mean however the plane is not required as to achieve that result I can just make the hole on the leg and the hole on the stay coincident. I'm still left with the 5mm gap either way.

I like b's idea re ball joints, however that idea would mean the two legs would never want to move together as the stay would not be constraining them at all.

I can put an 's' bend in the stay to take up the 5 mm gap however in the real world its not required.

Charles

 

[CorBlimeyLimey]

The legs don't become locked on my computer.

The ZIP file you posted doesn't contain the "Metric\washers\Flat Washer Narrow_AM" part so the mates connected with it are suppressed/broken. Maybe it has something to do with that.


Helpful SW websites FAQ559-520
How to get answers to your SW questions FAQ559-1091

 

[charliedurrant]

CorBlimeyLimey,

I am a limey!.... I have replaced the washer (it was part of the toolbox) and uploaded the lot to the same location. If you know of an easy way to replace a part with another but keep the mates I wouldn't mind knowing.

The legs are not constrained to move towards each other but with each other about the set screws which holds them to the apex joint when the stay is in place. If it however is OK on your machine then I will look a twit as it would seem I just can't use 'move component' !

Charles

 

[SnowCrash]

What about making the flexing tab at at the end of the tube a separate piece and constraining it to flex like a hinge?

--
Hardie "Crashj" Johnson
SW 2005 SP 4.0 (reluctant to change)
Nvidia Quadro FX 1000
AMD Athalon 1.8 GHz 2 Gig RAM

 

[charliedurrant]

SnowCrash,

Thanks for the comment.

It is constrained like a hinge, well atleast its mated so and seems to move like I expect - note I am new to cad drawing in all aspects.

Movement in that direction is ok, its roation about the joint of the leg to that tab that is the issue. It would ofcourse only be possible to know that if you downloaded the assembly and not just the e-drawings file.

Charles

 

[charliedurrant]

SnowCrash,

Or maybe I misunderstand you. Do you meen the flattened part of the tube. It is a seperate part, but how do you mean to constrain it lige a hinge?

Charles

 

[charliedurrant]

Also, as an aside what is the standard way to hang something from something else. Are planes the best way?

A real life example would be: How would you model a ring hanging from a hook?

Charles

 

[smcadman]

A few suggestions:
First suggestion:
I try to create a sub-assembly the way it would be created in "real life". Your assembly "Assembly Folding Brace" has 10 components, 4 of them should be 1 sub-assembly:
Folding Brace Part B
Folding Brace Stop
Bead9
Bead10
This would result in less mates required at the assembly level (cleaner, easier to troubleshoot).
To create a sub-assembly, pick the 2 parts only (beads won't work), right-click menu, down arrows, then pick "Form Sub-assembly here".
See screenshot:

http://img119.imageshack.us/my.php?image=formnewsubassemblysb4.jpg

Name the sub-assembly and add the weld beads in the new sub-assembly. Delete the unnecessary weld beads in the other sub-assembly.

Next suggestion:
I usually mate 2 parts to each other first without hardware. The screws are then added later. This way you can pick 2 parts/assemblies in the tree and easily find out how they are mated. For example, in the top-level assembly you posted, CTRL+pick Assembly Apex and Assembly Leg, then pick the middle-tab in the task pane. This is the "Property Manager". The mates of the selected models will be highlighted. In this particular case, there are no highlighted mates. So you will have to go through all mates to see why your legs won't swing.

As for your "real world", I would make another configuration, one that is static and locked for your drawing, another that isn't locked to test motion. Actually it is a cheap kinematics, and you may need it to fold completely for packaging (what size box do I need). On the top level assembly, under advanced mates pick the angle option. This will keep your folding brace from folding/unfolding too much.
Finally, for the gap, you would only need it for illustration purposes only, so make a configuration of Folding Brace Part A and put a slight offset too close the gap. For shop drawings, show the flat part.

Flores
SW06 SP4.1

 

[charliedurrant]

scmadman,

Good points - I have done what you said re the sub assembly and an excellent point re the angle mate. It now doesn't fold back on itself - I managed not to notice the advanced mates.

For the 5mm gap simply model it as it theoretically should be and be done with it. Agreed. I guess slop doesn't exist in computers! I have updated the 'Assembly - Side.SLDASM' at

http://www.wilverley.com/Assembly.zip

So all this now leaves is the rotation of the legs where they are fixed to the apex joint. They moved before the brace is added but not when it is in place which... just isn't right ....or are you saying that I need a static configuration and it can't be done.

Charles

 

[CorBlimeyLimey]

The mates causing the "problem" are "Concentric31" and "Concentric34". These are constraining the legs to the Folding Brace such that the legs cannot be moved sideways.

If you could dimple or csk the holes in the leg & use a spherical faced washer, you could then use tangent mates between the sphere & the csk which should allow the sideways movement you need ... for the model. As you mentioned though, in real life, the retaining screw would not allow the rotation to occur without flexing of the brace.


Helpful SW websites FAQ559-520
How to get answers to your SW questions FAQ559-1091

 

[CorBlimeyLimey]

By the way, when I posted earlier that the model worked OK for me, I did not realise you were trying to move the legs sidways.

One other suggestion, instead of making the leg an assy, it could have been created as a part. See compress a tube in solidworks thread559-148035


Helpful SW websites FAQ559-520
How to get answers to your SW questions FAQ559-1091

 

[charliedurrant]

So, in effect make the attachment between the leg and a brace a ball joint ( as per bvanhiel, just in a different way ).

Now I may be over discussing the point here and I understand that the concentric mates are preventing one leg from moving away from the other but I should be able to move both legs at the same time as I can on the live frame since this will retain the alignment of the concentric mates?

Either way I'll try the ball joint idea.

Charles

 

[charliedurrant]

Grrrr, I can't get a ball joint to work....I'm having a bad week. I decided to try a reference point mating to a spherical surface as a test but the mate is not allowed. SW goes on about the distance being Xmm away.

I'll battle on. I tried to search for ball joints on this forum but the link to the example is dead....Grrr again.

Charles

 

[CorBlimeyLimey]

You should be able to move the legs sideways in SW only if the legs are parallel, otherwise the sideways movement would be through a compound angle. You should be able to do that with configurations using angle mates, but not with a flexible assy where the parts are manually moved.

FYI, in the ball joint (joystick) example, the centres of the Ball & Socket were placed at the models origins and the origins were then used in a coincident mate. A plane perpendicular to the joystick handle was then used in a limit mate with a matching plane in the socket, to limit the amount of joystick "tilt".


Helpful SW websites FAQ559-520
How to get answers to your SW questions FAQ559-1091