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VEX Robotics
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Overview
For two years, I built robots to compete in the annual VEX Robotics Competition, where robots played a 2v2 game and scored points in order to win. This article is on the robot I built in Fall 2018.
Role
- Team Member
- Designer
- Builder
Team
3 Students
Course
Extracurricular Competition
Date
Fall 2017 - Fall 2018
Problem
We had to build a remote control robot that was able to maneuver around the playing field and manipulate game elements in order to score points. The robot was also to be designed based on the game strategy that the team decided on.
Constraints
Design and build a robot with the following constraints:
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No larger than 18" x 18" x 18"
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Must have a 30 second autonomous program
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Must also be able to park at the top of the central platform to gain extra points
Prototyping
We decided that we wanted a small, agile robot that could sneak around the field while our teammate fended off the opposing team. While our opponents were preoccupied, our robot would flip "caps" (pictured below) in order to take points away from the other team and gain them for our own.
Credits: VEX Robotics
For the drivetrain, we went through several prototypes. In order to climb up the platforms, we decided to incorporate wheel legs (pictured below). The first iteration lacked traction, so we utilized gear ratios to increase the torque produced by the motors. We then replaced the front wheels with omni-wheels to increase the turn speed of the robot.
Credits: VEX Robotics
For flipping the caps, we decided to go with a forklift-like design. Chains and sprockets on each side moved the fork up and down. When the robot drove forward and lifted the fork, the caps were successfully flipped.
We were quite happy with the strategy and design we managed to come up with, and were eager to take it to our first round of competition. Making it to the quarter-finals, our robot was matched up against a strong opponent in an entirely different weight class, and we carried our robot back to the lab in several pieces.
A Better Bot
The competition taught us a lot. For our second iteration, we were faced with the problems below:
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The chains and sprockets on either side of the lifting mechanism weren't in sync, causing the fork to be tilted and straining the chains, increasing the risk of the links snapping. This was likely due to inconsistencies within the motors.​
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The fork itself was prone to disconnecting from the chain and sprocket, likely due to a weak connection. This was especially problematic when the robot experienced large forces.
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The motors for the drivetrain had similar inconsistencies. When rammed by a larger robot, sometimes the wiring connections would be broken and a wheel would stop working. This would cause the robot to turn unexpectedly or slow down.
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The robot was unnecessarily large. The internal supports were comprised of hollow aluminum standoffs, so the larger size meant less structural integrity. This was our primary weakness when we got rammed by a larger robot.
In order to address these issues, we made the following adjustments to the robot:
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Added rigid supports between the chains to ensure that the two sides were in sync.
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Reinforced the connection between the fork and the chains
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Connected the front and rear wheels on each side with chains and sprockets. This ensured that the wheels worked in sync and the robot would still be able to carry on even if one wheel was incapacitated.
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The entire drivetrain was compacted.
Final Product
The final design was taken to a second round of competition, in which we faced more opponents and managed to reach the semi-finals, successfully flipping a robot thrice our size and weight off the central platform but sacrificing our points in doing so.
What I Learned
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Iterative Design Process
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Teamwork
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Component Design
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Top-level Assembly
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