Introduction: How to Design a FTC Chassis in Fusion 360 - Make It Spin Challenge

In the FIRST Tech Challenge, student teams build robots and compete in yearly games. While many teams don't use CAD software, the best robots are consistently designed digitally and built only after fully 3D modeled.


This year, my team 20381 Killer Instinct has striven to fully design our robot in Fusion 360, developing our most advanced robot yet. This guide is meant for teams in similar circumstances to us who are looking for resources on how to use CAD to build their robots.

Supplies

Required:

  1. Fusion 360 (or similar CAD program)
  2. Computer

Recommended

  1. Some form of CAD mouse (aka SpaceMouse by 3Dconnexxion)

Step 1: Know Your Game

Whether you are in a FTC, FRC, or VEX team, you need to first understand the ins and outs of your game. Before you begin designing, you need to have a clear idea of what you want your robot to do. It is difficult to go back and change features within a large CAD design, so I suggest to spend time on what you want your design to be.

Step 2: Have a Strong, Versatile Core

When it comes to designing your robot, you need to start with a strong, versatile core for the heart of your design. For this season, we went with a U-channel core, which housed our drive motors and provided a great base for the rest of our robot.


I suggest that you avoid custom designed pieces when it comes to this, as it will be easier to build off of when you are just getting started. Our Chassis Core includes our drive motors, motor clamps, mounts, as well as our Pinpoint Odometry system and sensor fusion computer.


This is also a great opportunity to accustom yourself with fasteners in Fusion 360. A good CAD model incorporates everything, including nuts and bolts, so while they are extra effort, they make your model stand out. There are 2 ways to do this in Fusion, either use the Fusion Fastener tool (which automatically aligns nuts and bolts as well as applies joints) or use the built-in McMaster-Carr library (which has better libraries of components.)


However you do your chassis core, ensure that is it strong and applicable for your robot. Our chassis core was designed for a completely different robot, but so versatile that we used it for our current season, Decode.

Step 3: Start Your Drive Chain

Before you ever start on an intake, out-take, or any other components in your design, you need to start thinking about how your Drive Chain will stay together. The popular choice of many teams is to use flat panel or sheets of different materials, such as aluminum, acrylic, or polycarbonate. I suggest using flat sheets since they are easy to machine (CNC, laser cut, band saw, etc).


I started by attaching a large square plate to the side of the Chassis Core. By starting with a large, basic shape, you can easily add components, then reshape at the end. Start making your wheel assembly with your Chassis Core, beginning by mounting your motors. Also main sure to keep up with your fasteners throughout your design.


You should decide how you want your motors to move your wheels, whether you want to use direct drive, timing belts, gears, or chains. As you see in our design, our back wheels are direct driven, and our front wheels are belted.


NOTE: The most important part about such an in-depth design is to have good external components. Your Chassis should really only include custom parts that you will machine or 3D print, do not model your motors or have assets within your design that aren't saved in their own version.


What I mean by this is have almost all of your parts saved as their own version, we personally keep a folder of every STEP file that we use. That makes it easy to import them into the design. It also allows us to integrate joints really easily. For example, our Yellow Jacket motors from GoBilda have their axel on a revolute joint in their own design, and we simply import the linked design into the Chassis file.


Keeping good organization is key. I like to organize all components by side or assembly (aka Left Side Assembly, Intake Assembly, etc). You can also apply motion joints to make things move, which is great for previewing motion limits (Things that spin!)

Step 4: Begin Your Mechanical Subsystems!

Now is the fun part, you get to design the different subsystems of your robot, intake, transfer, out-take, claws, arms, extensions, anything you want! While doing this be sure to remember your fasteners, and keep good care to keep all of your sketches constrained, because you will have to go back and change things if your design doesn't work out.


I would also suggest making your subsystems as simple as possible within Fusion. This includes keeping all of your system's components saved somewhere else (we have our intake Rubber Band Spool modelled in its own design). This limits possible Parametric errors that can result when Fusion computes your design (when your design is months old and has saved variations in the triple-digits, this can happen a lot.)


For example, for our out-take shooter, we aligned all components where we wanted them, and extruded plates on both sides for mounting. With your parts in place, making mounting is easy by using the Project tool in the Sketch mode and the Extrude tool in the Build mode. You can also use the Automated Modellingtool to connect different types of mounts. For example, you can see our LimeLight camera, which is mounted with the help of automated modelling to connect the mount to the side plates.


I suggest also importing your game's field elements as STEP files. Companies like Andymark and GoBilda give all of their STEP files for free, so take full advantage of those files. Your design should really be 75% importing STEP files from online, and 25% designing custom parts for your bot.

Step 5: The Little Things

Now that you have your main components modelled, its time to polish off your design. This includes putting the different, smaller, components into your design. This includes parts like:

  1. Battery Mount
  2. On/Off Switch
  3. Control Hubs and Expansion Hubs
  4. Electrical Componentry (if you have anything extra)
  5. Belts (good for renders/pictures of the design)
  6. GoPro or other equipment


These parts really make your model great, since they take your design from being purely functional for your bot, to being art ready to be shown off. This is also really good for your portfolio, since you can get images from Fusion of any part of your robot, which are superior compared to photos.


This is also about the time that you want to optimize your design. This most includes pocketing your plates or parts to remove non-critical material and shave weight. I highly suggest waiting on doing this till a later time, since it becomes increasingly difficult to add onto a design that is pre-pocketed.


Here you can also start to familiarize yourself with the render environment for getting stunning renderings of your robot for portfolios, posters, sponsors, etc. Fusion has a really great library of materials, so make your design stand out by giving it color!

Step 6: Make It Spin!

Now that you have your design fully made, build it! Export the parts that you need to manufacture to their respective applications and make them. Assembling the robot will be very easy with CAD to walk you through it, and we have seen increased build productivity following a CAD model.


You will likely have to go back and change things, which is why it is important to keep your design clean and free of parametric errors. If you are new to Fusion, this will take time to learn, but once you become adapted to the habit of constraining sketches and keeping your components clean, this will be easy.


As your build, make sure to test out your assemblies, and Make it Spin!


Our robot this year has many spinning parts. All of our wheels turn (duh), but there are many other parts that turn as well. Our intake rollers spin at over 1000 rpm to intake Artifacts (this year's FTC game element). Our shooter, known as Shock Shooter, has many different spinning parts. From a flywheel roller that spins at 2000+ rpm, to a turret that spins the entire upper assembly at over 5 revolutions per second, its safe to say that we have experience with Making It Spin.




We have a come a long way from a couple of years ago. None of our new chassis design and robot this year would be remotely possible without Autodesk's free access to Fusion 360 and its online features. Fusion 360 is Killer Instinct's premier 3D modeling program, and has helped us to achieve what we have so far.