Why should teams use CAD?
Why? Well for one it is a great way to visualize and present your ideas, especially if sketching isn’t your strongest skill. It also provides a sort of guide for when you actually start building. If you just build it with no model, sometimes you discover things you had overlooked, and so you have to take it all apart and try something else. But if you CAD your robots first, you discover such things before you’ve started building, and don’t need to take anything apart. You can also use CAD software to almost create a set of instructions for yourself. you can build everything exactly as the CAD model shows and you know it will work. Plus I find it enjoyable. Its like building a robot, but without actually building a robot! Its also great for engineering notebooks, judges love those CAD blueprints.
Examples of what you can do with CAD
I want to make a drivetrain, but it seems like every time I do I overlook something with the wheel spacing or motor placement and it messes up my entire plan. So I’ll CAD one in advance!
Now I have an exact model of my drive! I did it all with free software and no physical parts, and now I know I’ll be able to assemble it all according to plan once I start building.
(this isn’t actually my drive, I made this a while ago.)
And lots of highly competitive teams use CAD as part of their design process.
Take 240P for example
I highly recommend all teams that have access and time to CAD do, it ends up saving time and energy later on, and is a marvelous tool we have easy access to.
I use Autodesk Inventor, which is free for all students and competitors, and has a ton of updated part libraries for easy assembly. But there are other options as well, Solidworks, and Fusion are other common CAD programs.
Why use CAD? Here are some thought based on 30+ years of engineering experience (long post).
“D” is for design. Without doing any design, you are just tinkering. Granted, VEX lends itself to building tinkerbots with all the convenient hole-spacing and pre-engineered gear systems, but a little design goes a long way, whether it be on paper or by a CAD system. I’m older than dirt, and when I worked for La-Z-Boy for a few years, we built cardboard models of mechanisms pined with thumbtacks to make sure they operated correctly. It’s a lot easier and faster with the “CA” for computer aided, but it’s not essential, design on the board works, it’s just slower.
CAD modeling speeds up the design process, once you become proficient. This is probably the largest hurdle to overcome. Anyone who uses CAD on the job can just about model a drive base before you can even get your tools out and open a box of c-channel. The learning curve is what holds most people back, and until you do become proficient, it seems like a slow process. Now is a good time to start learning. If you want to use and AutoCAD product, just download it. For SolidWorks, your team’s mentor will need to apply for a grant to get the licenses. Start by learning the basics of assembly and doing “Computer Aided Documentation” by modeling your existing robot, and then begin looking at new designs.
Of course, if you have any 3D printed stuff (allowed in VEX-U), you must have CAD models.
A word of advice when using parametric CAD (3d models): set up a folder where you save your assembly, load your part models or libraries, then DON’T MOVE THE LOCATIONS OF THESE FOLDERS! Your model will completely blow up in your face if you move a folder location improperly. The cad packages have a feature called “pack and go” which is the ONLY way to safely move a parametric CAD model.
One last on-the-job example: I had to install inspection cameras and laser profiliometers on a robotic laser welding line. My physical access to the line was only 6 hours per week, as the line ran 24/7 except for a small window for p/m. The only way to get the job done was to model the important parts of the line from the old paper drawings and cell-phone photos from a distance, then verify the critical dimensions during one of the p/m periods (since nothing is ever exactly to print). Once I had the model, I could build all the mounting brackets I needed, create drawings for fabrication and send them out, and make installation drawings. The next week during the 6-hour period, the maintenance crew drilled and tapped all the mounting holes for the new equipment according to the CAD, and the third week, the equipment was all bolted into place. The great thing about CAD over tinkering is that I could “float” the models of the profilometers in exactly the right position in the model, then “build” the mounts to connect the devices to the machines.
Here’s my reference paper with links to CAD software and libraries: CAD for VEX Robotics.pdf (81.6 KB)