Some mechanisms and linkages seem impossible to design. You know exactly where each part should be when the mechanism moves, but working out the length of each link and each pivot location can be a daunting task. There’s just too many variables and unknowns. I’m not sure which is easier: trial and error or solving simultaneous equations?
You could buy mechanism synthesis software, but that can be expensive – especially if it’s not something that you do every day. Alternatively, you could use the new Managed In-Context Editing tools in Onshape to help solve your linkage design problems.
With Managed In-Context Editing, you can design your parts in the context of a higher level assembly. This ensures that everything fits together nicely. However, as in the case of mechanism design, you can also use these unique tools to design parts in multiple positions. The example in the image below is the in-context design of a tablet stand that has an adjustable viewing angle. Rather than having to approximate the position and angle of each notch that needs to be cut out of the back leg, you can move the components in the assembly, create a new Context, and edit your design so that it fits perfectly.
The beauty of Onshape’s in-context design tools is that the parts DO NOT update every time you move the components in the assembly to test motion. When and only when you need to propagate changes down into your parts, you can. That’s why we call it Managed In-Context Editing.
So, that got me thinking. If you can design an assembly in multiple positions, then you can design a mechanism. With just a few clicks, I created a viable design in a matter of minutes. You can see how I did it in the video above. It’s pretty cool, don’t you think?
The folding step stool is a relatively simple example, mainly because it’s a planar linkage. However, next time I have a mechanism to solve, I’m going to try this method. If anybody has solved something more complex, it would be great to hear from you! Please post your results in the Onshape forums.