Design of a FIRST TECH CHALLENGE robot in 5 days
By: Neo Wang
Tags: Robotics, Rendering, High School, Design, Competition

Introduction

As a high schooler participating in FIRST, I naturally like to build robots. However, robots cost money. In the offseason, it is both costly and grants us no competitive advantage to build robots. Usually, this time is spent doing 3d CAD modeling and preparing autonomous routines for the upcoming season.

As a result, I decided to ask two of my friends to compete in the Valor CAD Challenge, a competition to determine who can design the best robot in one week. Teams can be made up of up to 3 people, and the competition is based around a hypothetical FIRST game. This year, it was SuperShot, a frisbee shooting game.

Render of the SuperShot field

The rules and guidelines for the game can be found here. Reading this is strongly recommended to be more familiar with the challenge.

A .STEP file of our robot can be found here.

Tools used

Dassault Systèmes SolidWorks — CAD Modeling Fusion 360 — CAD Modeling and Photorealistic Rendering Keyshot — Photorealistic Rendering Gravit Designer — Robot graphics Slack — Team communication

Design Process

At the game release, our team’s brainstorming strategy was to brainstorm ideas for all subsystems and then divide each subsystem to a person. This proved to be effective: almost all of the ideas were unique in one way or another, and it was somewhat easy to distinguish which ones would be viable or not. For us, this made sense since, from actual team experience, multiple people working on a single subsystem often leads to repeated steps, meaning wasted time.

Drive Subassembly

Our philosophy was to keep the drive base simple. Since in other FTC games, the use of a mecanum (aka Swedish Wheel) chassis would provide finer control, stability, and maneuverability without sacrificing the speed of a tank (otherwise known as a 6 wheel drive) drive, we decided to design one for this game. Our time was limited (5 days), so we wanted to finish this assembly as quickly as possible as to mount the other sub-assemblies on top. Naturally, we gravitated towards the use of aluminum box tube extrusion, as it is both lightweight, durable, and relatively easy to work within 3d CAD software (for this competition we used a combination of both SolidWorks and Fusion 360). We assembled the frame in an H-Shape, as shown below:

Our drive assembly for the VCC with several mounts attached

Another core design feature of our drive was the 3 odometer wheels located as shown below:

The two mini wheels are 2/3 of our odometry pods

These wheels allow the robot to triangulate its position by measuring the delta in encoder ticks for each of the wheels and accumulating them over time. A more detailed paper on this system can be found here.

Frisbee Shooter Subassembly

For example, we brainstormed the following ideas for our frisbee shooting subassembly:

Vertically-oriented shooter Horizontal-oriented shooter Diagonal-oriented shooter Linear extension

Our frisbee shooter

As we took a closer look at the proposed linear extension implementation, we determined that the extension would be far too slow as our robot would have to travel the distance of the field to score. It was at this point that we decided a frisbee shooter was needed. Since our proposed frisbee-intake takes in the frisbees horizontally, it would make sense that we would choose a horizontally-oriented shooter, as the transfer mechanism from the frisbee-intake to the shooter would be simpler.

Also since seperating the shooter’s rotary (actual rotation of the turret vs the flywheel) motors would be relatively easy, and we had a bit of spare time, we decided to powershare the motors using a differential.

Frisbee Intake Subassembly

The shape of the frisbee proved to both be a challenge and an ally.

The 6" diameter disks used for the CADathon

The challenging part was that the disk was relatively hard to pick off the ground, as there is a hollow cavity separating the middle portions of the disk and the ground. However, the circular shape meant that it would be aligned no matter which angle it was grabbed from. Since the disk was low to the ground, it was clear that a low-but-wide vacuum cleaner type sucker would be the best fit for the task.

Render of our intake

Our design consisted of a belt-driven intake because it allowed us to contain the motor within the area of the intake. Also, directly driven motors tend to break much more easily because all the load is placed on the shaft.

Our motor belt transferred power to the conveyer belt system which would then transmit power through the the outer blue roller of the intake (we ran a hex axle through the conveyer belt which connected by another pulley to the blue roller).

Climb Subassembly

Extended render of the climb

We noticed that the area that we need to climb was located relatively high off the ground (23") and because of the 18" x 18" x 18" size restriction placed on our robot, a compact but robust extension system would be ideal. As a result, we implemented a straight winch-driven linkage to climb. The subsystem would extend upwards quickly (<1 second in simulations) and the robot would be off the ground in ~1.5 seconds.

A topology study was used to optimize the selective pocketing to lighten the climb.

Retracted render of the climb

Integrating Subassemblies

Since the workload of all the subassemblies was distributed among me and my other two teammates, we would need to figure a way to combine these subassemblies without fighting for space. To accomplish this goal, we created an approximate 3d layout sketch of the robot. Each subsystem would be placed in its associated region, to solve the conflicts.

There are several challenges we encountered while integrating the systems.