3 lb beetleweight

A 3 lb fighting robot, built from scratch.

We're Bots of Prey, two high school students. Reduction is our beetleweight: a green TPU frame, carbon fiber decks, belt-driven four-wheel drive, and a hooked steel blade on a hub motor. We designed it in Autodesk Inventor, built it, and fought it at GSCRL. If you have questions about any of it, get in touch.

See the build Download CAD

CAD render of the robot: a wide green frame with carbon fiber top deck, tan treads at each corner, three steel tines in front and a dark hooked blade between two green uprights.

GSCRL Mechanical Mayhem, Season 5 opener.

We finished 5th in the 3 lb beetleweight class. Every match showed us something about the robot that we hadn't caught in CAD.

We were knocked out in the winners bracket, so our final ranking could be anywhere from 5th to 9th.

The finished robot on a wooden floor, low front view showing the steel tines and green uprights. — The real robot, after the event.

In the arena

Stills from our match videos at GSCRL. They're low resolution, but you can see the robot driving and taking hits.

The robot tilted mid-hit, showing the chevron-marked weapon shield and red LED. — Mid-match, tilted by a hit.

Overhead view of the robot from one end, wheels inside the green bumper.

Oblique overhead view of the robot on a debris-covered arena floor.

The robot driving across the arena, rear three-quarter view.

Top-down view of the full robot in the arena.

How the design changed

We modeled the robot in Autodesk Inventor from photos of the real thing. The early versions got things wrong that took a while to spot. Here's how it changed.

Early CAD: bare green chassis with a carbon deck and a notch for the weapon. — Rev 1
Chassis
Frame, bumpers and top deck, sized around the 51 mm wheels.

Second CAD revision with a belt-driven drum weapon and four tines. — Rev 2
Drum weapon
From the photos we first guessed a belt-driven drum with four tines. We'd read the pictures wrong.

Current CAD revision with a single hooked blade and three tines. — Rev 5
Hooked blade
A single hooked blade, three tines mounted in channels, flush screw seats, and a steel shield facing backward over the middle of the robot.

This isn't our latest CAD. We keep improving the robot faster than we can update this site, so the model and renders here are behind the real thing.

What we're building next

GSCRL showed us where Reduction is weak. Hammers and overhead weapons landed on the flat top, the rear wheels took direct hits, and repairs between matches took too long. This is what we're changing.

Armor

Rear-wheel guards. Protective guards around the back wheels to cut down on direct hits, while keeping enough clearance for the wheels to spin freely.
Fully angled top armor. Sloped panels instead of a flat top, so hammer and overhead hits glance off.
Reinforced armor supports. More structure under the top panels so they don't cave in.
Better side protection. Cover exposed components and thicken the edges and corners that get hit most.
Stronger front wedge. A better wedge angle and stronger mounting points for head-on hits.
Replaceable armor panels. So we can swap a damaged section between matches instead of rebuilding.

Inside the robot

Protected internals. Better mounts and padding for the battery, electronics and wiring so hits don't shake things loose.
Easier maintenance access. Access panels that make battery swaps and repairs faster in the pits.

Driving

Traction and balance. Different tires and better weight placement for more pushing power.
Self-righting. Either a way to flip back over, or a layout that drives fine upside down.

Some of this is already in progress in CAD, starting with a stress study on the weapon carrier. It's on the build page.

The numbers

The main specs.

1,127 gEstimated weight. The 3 lb limit is 1,361 g

290 × 215Footprint in mm, tines included

4WDTwo brushed gearmotors, each belt-driving two wheels, on one dual controller

~$490Parts and fabrication

The full parts list

Every part with its weight, dimensions and price. You can turn parts on and off to see how the total changes. If you want the CAD, email us and we'll send it.

See the build