Constraints with the square holes in VEX parts?

Next year I want to get my kids to design their robots in Inventor (very nice software, thanks AutoDesk!). So I’m doing some experiments and tutorials with it myself to become familiar with it.

Does anyone know of a good way to easily constrain things to the square holes in the vex parts? When you have circular holes, its very easy to constrain a screw to the hole for example but I haven’t found a good way to line things up to the square holes.

There are lots of cases that come up. One case is aligning a screw (round) with the center of a square hole. Another case is aligning the circular hole in a bearing with the square hole in a plate. Another is when I want to line the square holes in two plates (this can be done by aligning the two surfaces of the holes if its a multiple of 90degrees but what if you want a brace at an angle?)


Create a circle sketch on the surface of the part. I’ll try to post an example in a little bit…


I hadn’t thought of that. Do you edit the part to put that sketch on it or is this something you can do while creating the assembly?


Either. To do so in an assembly, double-click on a part, and then you can edit it just as if you’ve opened the part in another window/tab.

Someone just posted this in another thread:

“My solution for constraining bearing blocks (or anything in a square hole) is to use a WorkAxis (or two). Create the axis using the intersection of the two planes inside the structure hole and then offset by 0.091 (half the square hole dimension) from both.”

That sounds like it would work pretty well too. I’ll try both next time I’m experimenting.

This was one of my posts. I arrived at this technique as I did not want to be sketching on the original part files, I had converted most of the VEX step files to inventor part format, assigned properties etc. and saw this as a read only library to be used in assembly. I have tried creating sketches in the assembly on the surface of parts but this does not seem to allow axis constraints. The quickest way of off-setting the workaxis is to first create it, expand in the browser to show the two plane constraints, select each constraint in turn and enter the offset in the edit field at the bottom of the browser window. One annoying feature of workaxis in the browser is that they do not drag reorder in a similar way to parts do so it’s takes some discipline to keep everything organized. Once the workaxis have been used the visibility can be turned off.

A method that I just discovered, which suits my needs fine, is as follows:

1: Use a flat mate constraint to mate the bottom surface of the delrin to the upper surface of the (eg) c channel.
2: Use a tangent mate to mate the cylindrical hole in the bearing to the flat inside surface of the hole in the c channel, with an offset of 0.0075". This lines it roughly up so that the holes are centered.
3: Repeat step 2 once or twice more on the bearing so that it lines up with the holes in both dimensions.

This method constrains the pieces so they won’t go haywire later down the road, and uses simple constraints so it’s a no fuss method for using the pieces sans modification.

What I do is create the circular surface in a corner hole. Pattern it, and then apply imates to all of the surface axels. After that I hide all of the surfaces in the pattern. It works very well and I have started a repository so that other poeple can use it.
Click here to get them. You can just click each part to download it, as I have not taken the time to create an index file in php, that lists all of them with src links.