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- The Goal -
To improve on the failed design of my previous BattleBot, Sweet Revenge, that competed on the 1st season reboot of BattleBots in 2015. In the re-design, all loaded parts should have an FOS higher than 3 and designed for manufacture.
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Executive Summary
In 2015, I had the incredibly opportunity to lead and compete on a team on ABC’s Battlebots. Having no CAD experience, no analysis skills and no developed engineering skills, it was definitely a challenge. As team captain for an all-girl high school team, I was proud to represent girls in STEM and my school. But things don’t always go as planned—especially when you don’t have a CAD or any FEA or FOS to predict possible failures. Ultimately, our robot Sweet Revenge, lost in the battle due to weapon malfunction. And now the time has come to re-enter my ~imaginary~ arena and avenge our loss. For my final mechanical design project, I decided to re-design my battlebot and create Sweet Revenge 2.0- a robot with all the same vicious and sleek design but with none of the failures of the original. The goal of the project was to design a semi-complex CAD (25-50 parts) with 3 transmission systems, run full FEA and FOS on all loaded parts, and optimize any parts with an FOS less than 3.
The battlebot consisted of 3 separate transmission systems. For the tire drive, I used one single brushed motor from McMaster, attached to two separate chain drives for each tire using Sprocket and Chain assembly. The chain drive and shafts rest on a central panel attached to the bottom plate of the battlebot. A tensioning system in added in case there is slack in the chain in the future. The robot was designed symmetrically so that the same tire chain drive design can be used for both sides. Both motors rest on individual motor mounts and are centralized in the robot in order to preserve center of gravity.
Lastly, the weapon drive was designed also using a sprocket and chain assembly, but with a 1.5:1 ratio. The chain is attached to a brushed motor and to the weapon shaft that goes through the weapon. The motor is mounted to the bottom plate with a motor mount and has slots for tensioning the chain. The weapon is made from AISI 304 machined steel and is held to the shaft using a bolt. CAD Models and Summary
FEA and FOS Analysis & Optimization
After developing the CAD model, I did preliminary free body diagrams on all the loaded parts of the design. Using the same forces, I ran FEA on the 10 most loaded parts and then optimized all parts with a safety of factor less than 3. Below are just 2 of the optimized pieces I re-designed.
Before optimizing, the FOS for the motor gear spring pin was at 1.7. After changing the material from aluminum to AISI 304 Steel and making the pin solid, the factor of safety became 7.9
Before optimizing, the FOS for the Weapon Chain sprocket was at 0.34. After adding significant width to the teeth and changing the material to Steel, the FOS bumped up to 7.6
Final Design and Rendering
Assembly and Part Drawings Below are some of the assembly and part technical drawings I produced for this project. In total I created 1 full assembly drawing, 4 sub-assembly drawings, and 20 unique part drawings. |
