The black part moves like this, but the blue part moves like that.
May 7, 2010 4:48 PM   Subscribe

Is there CAD software that will allow me to build a mechanical linkage, and then manipulate it?

I want a piece of CAD software that will allow me to build a complex mechanical linkage, and then move it around with the constraints of the system simulated. It also needs to output a standard format that I could then send to a machine shop.

Preferably, it would have options for high-speed (automatic) rotation of the parts in question. Maybe gears meshing, timing belts, etc. Ideally, it would give me estimated forces on various parts of the apparatus. Even more ideally, it would allow me to specify materials for different parts of the linkage and tell me if they would break. It might also be nice if the software itself were no more difficult to use than, say, Lightwave 3D or Maya.

Let's pretend price is no object, as I want the answer even if it's a $40,000 piece of software running on an obsolete Cray. But, I'd especially like answers that will run on linux.
posted by Netzapper to Computers & Internet (10 answers total) 7 users marked this as a favorite
You can definitely do this with Pro-Engineer, but you may need to buy one of their add-ons (I think it's called motion-something-or-other). Solidworks should also allow you to do this.

In general, I've found CAD packages to be lacking in the rotation department, because most of them rely on dependencies in the form of "this surface connects to that surface". When you're rotating, you're constantly swapping surfaces that are interacting, which tends to confuse the software. That being said, I have gotten Pro-E to approximate gear rotation, but it was a huge pain in the ass.

If you want forces and deformations, you can import many different CAD files (including Solidworks and Pro-E) into Ansys, which will do a finite element model for you. Ansys is stupidly easy to use; it's one of my most favorite mechanical packages around.
posted by backseatpilot at 4:54 PM on May 7, 2010

Response by poster: To be more specific, a mechanical linkage similar to this rc helicopter swashplate.
posted by Netzapper at 5:01 PM on May 7, 2010

Preface: I am a former engineer with no contact with the last 6 years of magic software.

Packages like Pro-E and Solidworks are what you'd want to use, but it's not really something you just pick up and run with. Cutting to the chase, your lack of engineer-y jargon makes me think you might be embarking on a project that you'll need help with. :)

There's not really any software that'll be easy to use without at least a basic knowledge of mechanical engineering or material properties, I don't think. You're interested in finite element analysis, statics and dynamics, yield strength, elasticity, strain, fatigue, moments of inertia, etc. Stuff that engineers spend a *lot* of time learning.

It's complicated but not rocket science. The math isn't much beyond what lots of kids do in high school. Find a real enginer and talk to them about what it is you want to do or learn. Otherwise, go find a vector mechanics book and start reading.
posted by pjaust at 5:22 PM on May 7, 2010

FWIW, I totally don't mean to sound snotty about this. It's just that this is the engineering equivalent of someone asking about what the best way to start an IV and sedate a patient is. Most of it is stuff I don't understand at all, but I've spent enough time around mechanical designers to know that if I tried to design a swashplate I'd be asking to have a helicopter blade fly through my neck.
posted by pjaust at 5:29 PM on May 7, 2010

Response by poster: Okay, so I'll bite on the you're-not-qualified hook.

I'm a computer programmer. I've written finite element analysis software. The math isn't an issue. And I'm pretty highly autodidactic, so neither is the learning part. And my best friend is a mechanical engineer.

I just want a tool to help me visualize a design I have in my head. I'll do it in static CAD and have it machined, but I'm hoping there exists something like what I want. And this is a one-off project, not a product design. I'm risking nobody's neck but my own.
posted by Netzapper at 5:48 PM on May 7, 2010

I used Autodesk Inventor (a competitor to Pro-E) to create 3D models of parts and interactions in high school. It wasn't that hard. There's a 30-day trial, ~$4,000 to buy. Windows only, unfortunately.

Looks like Algor Express can import files and run stress analyses for free.
posted by djb at 6:20 PM on May 7, 2010

Alibre should be able to do it for you. There's an express version that's free, however it limited to no more than 6 parts in an assembly. Still, you can play with the free version and decide if you want to spring for the unlimited version (I paid $199 for it, but I think that was a special offer).

Within an assembly you can define constraints, such as an axle being constrained within a bearing. The only issue I had (and it might be my lack rather than the software's) was that I couldn't model a mechanical stop, for example a piece free to move along a rail is happily constrained to the rail, but I couldn't find any way to make it stop when it hit a end block at the end of the rail.
posted by Long Way To Go at 8:05 PM on May 7, 2010

Disclaimer, as a recent mechanical engineering graduate, I'm more familiar with the software itself than who's using what in which industries.

Having used most of the major CAD software (Unigraphics, ProE, Catia), IMO Solidworks has the quickest learning curve of any CAD software. It will let you generate things like gears. The mating of individual components in assembly mode is particularly intuitive, so you can constrain the relationships between parts and then move them around. Solidworks also includes some basic finite element modeling capabilities. While not as advanced as something like ANSYS, that might suit your needs just fine.

Now, if you actually want to animate your model, giving it set rotational speeds, try something like ADAMS. You can import models from Solidworks and establish mating joints with physical resistances, do kinematic analysis and get some cool (and useful) graphs.

Regarding the "standard format" for your machining, in my experience with a couple shops in the U.S. and Asia, sending a 3D model won't be sufficient. Unless you find a machinist that will figure it out for you, he/she is going to want relatively standardized engineering drawings. Luckily Solidworks, like all major CAD programs, has the tools to generate those drawings... just don't rely on auto-dimensioning.
posted by ista at 8:56 PM on May 7, 2010

I wanted to second ista above that SolidWorks is by far the fastest to learn and easiest to "pick up and run with" of the various CAD I've used. Additionally, I found it easy to create the files needed for machining (either to send directly to the machine, or to a human machinist), and had relatively little trouble with animation of assemblies up to about 20 parts, maybe 6-8 of them moving.

The one thing I found really useless in Solidworks was its help files, but that's what the internet is for. The tutorials for beginning to learn, though, were fantastic.
posted by whatzit at 11:32 PM on May 7, 2010

I've used ProE and Ansys for mechanism design and FEA, and I've heard good things about Solidworks.

If you want free software and don't mind putting up with lack of features (definitely no FEA, dimensioning is difficult), you might check out Google Sketchup with the SketchyPhysics plugin.
posted by sninctown at 8:17 AM on May 8, 2010

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