COWBOT
/ NDSU COMBAT ROBOTICS /
CONTEXT
Cowbot is a combat robot I led the development of during my sophomore year (2024-2025) at NDSU.
We competed in
Robobrawl's UIUC X,
a bracket-style competition where robots are
designed to disable or destroy opponents. Since no one on our team had prior robotics
experience, the project became a full ground-up effort in learning how to design for
impact, reliability, and performance under strict weight constraints. I lead
the team through the development of the drivetrain, weapon system, and overall mechanical
packaging, turning an unfamiliar challenge into a functional competitive robot.
After being exposed to Robobrawl the year prior, I became interested in the creativity and engineering behind combat robotics, which ultimately led to this project. My previous exposure to Robobrawl and experience in creating CAD models for our old robots gave me the necessary proficiencies on how to go about designing a battlebot. In the fall of 2024, I organized a group of 5 student engineers to take on this project. As the group lead, I organized design reviews, managed our BOM, and provided much needed mentorship to new members.
We registered for the 30 lb division and went forward through an 8 month development cycle, which culminated in March 2025. Oh and if you're wondering, its namesake was inherited from an elaborate inside joke.
After being exposed to Robobrawl the year prior, I became interested in the creativity and engineering behind combat robotics, which ultimately led to this project. My previous exposure to Robobrawl and experience in creating CAD models for our old robots gave me the necessary proficiencies on how to go about designing a battlebot. In the fall of 2024, I organized a group of 5 student engineers to take on this project. As the group lead, I organized design reviews, managed our BOM, and provided much needed mentorship to new members.
We registered for the 30 lb division and went forward through an 8 month development cycle, which culminated in March 2025. Oh and if you're wondering, its namesake was inherited from an elaborate inside joke.
DEVELOPMENT
Before we started our design, we had to consider a few basic considerations in mind:
The initial basic idea we wanted for Cowbot was similar to sloped armor that Soviet tanks from the second world war heavily employed. The idea is that an angled surface will have greater effective thickness in the normal direction, perpendicular to the vehicle base. Additionally, we theorized that loading multiple bends on one cut would be more efficient for manufacturing, and would also eliminate the need for much fasteners. With this first draft, we were prioritizing the structural frame of the robot before other critical aspects. Once we considered the spatial demands for a drivetrain, it was quickly realized that the concept would be rather difficult to pull off effectively. Additionally, accounting for tolerances on an assembly with that amount of bends, coupled with an inexperienced team, was probably not a good idea.
We settled on a "tab and slot" method for the chassis, which most other teams employed. For the drivetrain, we elected to use the NEO brushless motor and planetary gearbox sets for their ease of use. Chain drive was selected to circumvent frictional losses from a belt drive approach. For the weapon, a timing belt system was used to allow for efficient mechanical transfer while allowing for slippage upon weapon impact. 3/8" aluminum was chosen for the chassis as that was the available thickness that the club had in stock. HDPE was selected for the side skirts because it can plastically deform under impact rather than behave as a rigid member, helping absorb and dissipate kinetic energy. A large cover consisting of aluminum and plastic sheets protect the top portion to defend from overhead attacks, largely from axe or hammer bots. We prototyped our chassis by using laser cut wood of appropriate thicknesses to do test fits on our internal components.
The internal volume was made to be as compact as possible. As a result, our drive motors were in a staggered configuration. Our ground clearance was made to be as small as possible to prevent opposing vertical spinners from catching the undersdide of the robot. One minor deviation we made from the rest of the club was that we switched from DSMX to ELRS for radio protocol, which decreased our latency and increased our operational distance subtantially. While the impact on the overall project was relatively small, the decision reflected a broader mindset that shaped the build - we were willing to evaluate assumptions, compare alternatives, and adopt a different solution when it offered a clear technical advantage.
We built our development workspace in Onshape, which allows multiple team members to simultaneously model on the same project files, as all information is stored online in the cloud. Additionally, Onshape enables modeling through web browsers, opening up the ability for our team to work on almost any platform, regardless of their hardware specifications. Onshape also provides publicly available scripting tools for tasks such as weight reduction.
- The robot must comply with the 30 lb weight limit.
- The chassis should be rigid enough to withstand high impacts and carry loads from the spinning weapon.
- Materials must be relatively cheap and easily sourced (can't do titanium!).
- Electronics in the interior of the robot should be securedly fastened.
The initial basic idea we wanted for Cowbot was similar to sloped armor that Soviet tanks from the second world war heavily employed. The idea is that an angled surface will have greater effective thickness in the normal direction, perpendicular to the vehicle base. Additionally, we theorized that loading multiple bends on one cut would be more efficient for manufacturing, and would also eliminate the need for much fasteners. With this first draft, we were prioritizing the structural frame of the robot before other critical aspects. Once we considered the spatial demands for a drivetrain, it was quickly realized that the concept would be rather difficult to pull off effectively. Additionally, accounting for tolerances on an assembly with that amount of bends, coupled with an inexperienced team, was probably not a good idea.
We settled on a "tab and slot" method for the chassis, which most other teams employed. For the drivetrain, we elected to use the NEO brushless motor and planetary gearbox sets for their ease of use. Chain drive was selected to circumvent frictional losses from a belt drive approach. For the weapon, a timing belt system was used to allow for efficient mechanical transfer while allowing for slippage upon weapon impact. 3/8" aluminum was chosen for the chassis as that was the available thickness that the club had in stock. HDPE was selected for the side skirts because it can plastically deform under impact rather than behave as a rigid member, helping absorb and dissipate kinetic energy. A large cover consisting of aluminum and plastic sheets protect the top portion to defend from overhead attacks, largely from axe or hammer bots. We prototyped our chassis by using laser cut wood of appropriate thicknesses to do test fits on our internal components.
The internal volume was made to be as compact as possible. As a result, our drive motors were in a staggered configuration. Our ground clearance was made to be as small as possible to prevent opposing vertical spinners from catching the undersdide of the robot. One minor deviation we made from the rest of the club was that we switched from DSMX to ELRS for radio protocol, which decreased our latency and increased our operational distance subtantially. While the impact on the overall project was relatively small, the decision reflected a broader mindset that shaped the build - we were willing to evaluate assumptions, compare alternatives, and adopt a different solution when it offered a clear technical advantage.
We built our development workspace in Onshape, which allows multiple team members to simultaneously model on the same project files, as all information is stored online in the cloud. Additionally, Onshape enables modeling through web browsers, opening up the ability for our team to work on almost any platform, regardless of their hardware specifications. Onshape also provides publicly available scripting tools for tasks such as weight reduction.
SPECIFICATIONS
- Robot weight: 28.7 lbs
- Weapon type: Vertical modified drum spinner
- Weapon weight: 5 lbs
- Weapon motor: Castle 1512
- Weapon max RPM (theoretical):
- Weapon weight: 5 lbs
- Weapon kinetic energy (theoretical):
- Weapon power delivery: Mamba Monster X 8S
- Drivetrain: 2x NEO brushless V1.1 & 2x SPARK MAX ESC, Chain drive
- Battery: 5S 3600 mAh 18.5V 60C
- Armor: 3/8" Aluminum 6061, HDPE
- Dimensions:
CONCLUSIONS
The robot participated in two elimination matches:
Despite the losses, the more valuable outcomes of this project was the set of lessons we gained throughout the design and build process:
- Match 1 (Loss): The power bus at the rear of the robot came loose during impact, leading to momentary power loss through a short. The blackout was long enough to warrant a KO.
- Match 2 (Loss): The weapon was spinning in the wrong direction on impact, leading to the robot turning upside down and left unable to right itself.
Despite the losses, the more valuable outcomes of this project was the set of lessons we gained throughout the design and build process:
- Tolerances and manufacturing operations (drilling, tapping, milling, bending, waterjet, EDM, etc.)
- CAD modeling and engineering drawings through Onshape.
- Design for manufacturing (DFM) and design for assembly (DFA) principles, as well as designing for ease of maintenance.
- Material selection, resource management, and accounting for possible failure modes.
ACKNOWLEDGEMENTS
GALLERY
© 2026 Terrence Andre San Gabriel