Starting to CAD for FRC

For the upcoming season, my team plans to be a lot more thoughtful about our design process than we have in recent years. As such, we hope to be able to CAD at least a bit of our robot and plan ahead in regards to our robot’s design and layout.

I have experience working with OnShape and Solid works for hobby projects but never for robotics. I was wondering if anyone had any tips on getting started modelling gearboxes, large robot assemblies and the such. Thanks!

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I would suggest checking out 973 Ramp and Simbotics Solidworks tutorials. Those are two sources I used when learning to CAD that help me a ton.

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And if a full robot is daunting to you or your CAD machine: start with your dream pit cart. Working with simple 2x4 lumber in different lengths did wonders for getting our kids comfortable with CAD after years of not doing so. Don’t think you have to go replicating the latest Cheesy Poofs machine the first time out. :slight_smile:

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Knowing CAD is great. But there is a difference between knowing CAD and knowing design. A person that knows CAD can be told what to make and put it in CAD. A person who knows design has to come up with something to put in CAD (A mechanism, a type of drivetrain, ect.) So I recommend creating something to make your team think of a design for a task. There are quite a few resources on Chief and other places (even past FRC games) to design for. Design isn’t taught. It comes through experience.

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Thanks! I’ll definitely check those out.

Phew, that’s good :slightly_smiling_face: I like the idea of the pit cart, I’ll definitely check that out

Thanks for the advice! I’m going to start building that experience this summer and into the fall to be as ready as I can for 2020. I’m definitely looking into design over just plain CAD by itself

Also, while this isn’t exactly a tip for getting started with CAD, consider doing the CADathon this summer. You can find details on the last one here . We will have another one later this summer (late July/early August), will post details as soon we actually figure out the details (currently we’re all trying not to fail finals after champs).

You don’t need to be experienced in cad to participate, we have people of all skill levels participating and it’s a great experience to practice your skills and learn from others, and we can even partner you up with experienced cadder’s if you don’t have a partner of your own!

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Something which really helped me in learning how to design was going on the frc discord and talking to people there because there are some super smart people in there who have a ton of design experience. I also googled chief delphi+any question I had and there was usually a cd thread for it or a cd thread related to it and reading those gave helped me a lot.

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for robot assemblies the most important thing is organization. have a assembly and seperate folder for EACH sub assembly. There shouldnt be a single part in the full robot assembly only a bunch of assemblies. make sure to keep each part related to each subsystem in its coresponding folder and come up with a naming pattern.

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https://docs.google.com/document/d/1shW44-W7DLe-H2dGxqouhA0By1h0PQnkfFyFmKsadlI/edit Here’s a Google docs with a lot of the mentioned resources. Design would be best learned with the 971 and 1678 videos. (I should probs add those to the doc).

If I were to recommend you make anything, I would say drivetrains come first.

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HUGE tip: design your mechanisms with sketches instead of fiddling around with dimensions in parts.

A part of the core ethos of engineering is ‘iteration’, so the way I see it, the earlier you can iterate in your design the more informed you will be when committing your time and energy to CADding the full assembly. If you can create a sketch that will show you critical dimensions, and how your mechanism will interact with other aspects of the robot, it will allow you to quickly check sizing and tweak parameters on the fly. You would then use this sketch to drive dimensions in your corresponding mechanism CAD.

Here’s a sketch we used to drive our elevator and arm geometry - you can see how it’s pretty basic, but everything essential is in there. We have the scoring locations drawn in, and we are able to move the sketch around to see if our arm + elevator combo was able to reach all our desired scoring locations.

Along those same lines, don’t be afraid to use blocks as a placeholder for mechanisms. As long as you have a rough idea of how large a mechanism is going to be, put it in your assembly so that you can again check for sizing. After that, you can start gradually adding in more detail. My team’s gearboxes usually start off as just a blob of plates and gears, but after we get a better idea of how the robot is coming together, we tweak stuff and eventually make the gearbox “production-ready”.

When we do design gearboxes, we try and draw everything important in one sketch as well. Here’s the sketch for a relatively simple flipped-NEO gearbox I’ve been working on recently.

Essentially, with gearboxes like these, you’re choosing a target gear ratio, and then from there, choosing gears whose combinations allow you to get to that gear ratio. With gears, they transmit power along their pitch diameter, which is simply calculated by PD = # Teeth / Diametric Pitch. Diametric pitch (AKA DP) is simply the number of teeth per inch for a gear. In FRC we mostly use 20DP and 32DP gears (you’ll find 32DP more often in 775pro applications). With gears, we model them in sketches as circles equal to their pitch diameter, and we set them tangent to one another to determine their distance between centers, and thus where to put shafts and bearings.

I can elaborate on anything if needed! Feel free to reach out to me either here or on the FRC Discord.

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Adding onto this, set a hotkey for “show/hide dimension”. Same for sketch relations. I find it makes sketches way more palatable, letting you step back and see the “bigger picture” without tons of text.

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I talked to some CAD students at worlds, one of them gave a talk about CAD at a conference.

I was looking at how to teach Solidworks to 9th graders. Some of the things we talked about were doing projects. You can start with a drivetrain and break it up into many smaller projects. So far I have a list of about 18 projects mainly for drivetrains and I haven’t started on mechanisms.

One thing to keep in mind is you need to CAD to the ability of your team to fabricate the parts (hand drill, drill press, mill, CnC Router, Sheet metal). Realize that some dimensions on your parts are more critical than others. Don’t make non-critical dimensions too precise. If your line to line CAD data says to make a wheel shaft 3.951", see if 4" will still work. Typically every decimal point you add increases the time/cost to manufacture.

The other thing you should think about, but most don’t, is when you make assemblies in CAD is to make sure that you can put the parts together and also take them apart. What this means is that you can put in tool math to see if you have tool access to fasteners. It really sucks to find out that to remove that one bolt to change a motor you have to first remove all the scoring mechanisms from the robot.

Watch the 973 videos on sketch designing mechanisms. The great part of the video is that you can very quickly in CAD determine whether a design is possible. For example in this year’s game I came up with two sketches, of a single are at the center of the robot and another of an elevator to see if you could reach all the heights to score a game piece AND get back within the frame perimeter to start. You might find that certain designs need complex programming in order to stay within the rules.

A good CAD student should know how parts are made.
A good CAD student should know how those parts are assembled.
A good CAD student should use 2D drawings/sketches to verify that a design will work BEFORE you start modeling up parts in 3D.

And you thought you just wanted to learn how to CAD?

If you can do those three things you will be a valuable asset to the success of your team.

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Onshape is really easy to learn as there are tutorials for everyhthing. I have a document for tips to get started. Pm me if u need it

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Our team has found that cad programs that allow for easy sharing (ex. fusion 360) allow for a cad process that is more collaborative than other platforms

This is the primary reason why my team has used Fusion 360 for the last 4 years. Onshape also offers cloud sharing and has recently become popular in FRC.