Designing a Bridge Building Bot
This RC-controlled machine builds miniature bridges from plastic and aluminum pieces. It was built for the Machine Engineering class at Dartmouth and competed against two other machines. My team completed the bridge in 89 seconds, the fastest time achieved by cohorts in 2021 and 2022.
Timeframe
Sep - Nov 2022
Team
5x mechanical/ mechatronics engineering students
My Role
designing the bot’s arm; manufacturing and assembling parts for the entire bot
Tools/Skills
SOLIDWORKS, laser cutting, 3D printing, rapid prototyping, mechanical failure analysis
Overview
Objective
Create an RC controlled machine that can move, grasp, transport, position, and assemble PLA pylons, aluminum plates, and/or foam blocks into a bridge, allowing for a toy-excavator to cross the arena. Additionally, the bridge building strategy of the bot had to minimize the speed to completion, the amount of materials to build a bridge, and the weight of the bot, while ensuring the safety of Lego “pedestrians”, bot, and playing field.
Machine Overview
My team’s bot incorporated a crane on a rotating base, actuated by a lazy susan system. The arm, which I designed, was a truss structure meant to hold a pulley-actuated cart carrying an electromagnetic gripper, which could pick up PLA pylons and aluminum plates. Our strategy was to minimize time, materials, and maximize precision.
My Contribution
Aside from iteratively designing and analyzing the bot’s arm in SOLIDWORKS, I also fabricated most of the plywood components in the bot, 3D printed some components for the gripper, and assembled sections of the arm, cart, and gripper.
Final Result
So, how did we get there? Keep reading!
This is a picture of my team and the final version of our bot, assembled onto the playing field post-competition. I am pictured second to the left.
Process
Analyzing the Problem > Sketching & Rapid Prototyping > 3D Modeling & Failure Analysis > Iterative Manufacturing & Assembly > Competition
Sketching & Rapid Prototyping
We were given the general objective, a list of hardware and materials to use, and a lot of freedom. Therefore, we started by brainstorming bridge building strategies and big-picture systems to maximize our score, and converged to decide on a direction by combining successful strategies.
Design Principle: Keep it simple, stupid! The simpler the design, the easier it is to build the machine well, control it repeatedly, and perform well during the competition.
The pictures below showcase some of the process I followed, from big-picture strategies to focusing on the cart & arm subsystems:
Brainstorming of wheel assembly onto cart; for stability, we chose to use 8 wheels, 4 on top of the cart and 4 on the bottom, as seen in the front view in the top right
We brainstormed a rack and pinion (left) and a pulley system (above) to actuate the cart carrying the gripper. We chose the pulley system to reduce weight, although both would have worked.
Rapid prototypes made out of foamcore and plywood, to help idea visualization in the real world and highlight modeling and manufacturing insights, e.g. rotating the base to rotate the arm might be more stable and we don’t actually need 3 pulleys for a balanced system.
SolidWorks: 3D Modeling
Below are a few iterations of the arm assembly, modeled in SolidWorks, which I modeled and analyzed as a truss structure to reduce weight. The arm includes rails for the cart to slide onto, braces to fix the structure, and was made out of 1/4 plywood to maximize security. Retrospectively, I could have made it out of 1/8 plywood to reduce weight and the structural integrity of the arm would have been fine.
Below are a few snapshots of the arm integrated within the first machinery assembly we created, placed onto the playing field. We decided to actuate the cart carrying the gripper with a 2-pulley-mechanism, which I assembled and integrated into the machine model.
Iterative Design, Manufacturing & Assembly
This pulley stand actuated the rod carrying the gripper vertically, to lift and lower the building materials according to need. I was not its original designer, but I made the subsequent modifications and fabricated it in its final version. I added different versions of braces/supports to ensure the stability of an otherwise flimsy component when 3D printed.
During the manufacturing process, I fabricated different versions of the arm and cart. The pictures below showcase the final iterations, clamped after gluing. Below these, you can find a close to final assembly of the bot, a few days before the competition.
Below, you can see the final SolidWorks model and the final physical assembly.
Competition: Performance Demo
This video shows highlights of the competition to build a stable bridge as fast as possible. Check out my team’s perform at the very beginning of the video!
Check out the official Machine Engineering gallery, with pictures of the machines built for this class throughout the years.