Compromise (150g Combat Robot)

Compromise is my second attempt at building a UK Antweight combat robot. It fits standard UK Antweight rules, weighing only 150 grams and sized to fit within a 4-inch cube.

It is a 4-wheel-drive, lifter-spinner hybrid that takes clear inspirations from the BattleBots heavyweight Whiplash. Dual-weapon robots are rarely seen in the Antweight class due to the tight restrictions, and so it took some effort – and a lot of the robot’s namesake – to fit everything into a compact, functional package.

The build in its entirety was something of a jigsaw puzzle to put together. The motherboard fits tightly under the lifter arm, while the battery takes up the entire right side. The motor that powers the lifter arm is tucked away at the left side of the robot, and drives the left arm via printed gears. The spinning weapon is mounted directly onto a brushless drone motor at the end of the arm, and the cable for it loops behind the arm and over the lifter motor to connect to a tiny 20A speed controller. There’s absolutely no room left to breathe in there.

The robot is front-wheel-driven, with no extra motors spared. The back wheels are made of foam, spun on rubber band pulleys from the front wheels, and attached with 3mm nylon screws for axels. Together, this makes for the absolute lightest 4-wheel-drive solution. To my surprise, they held up in combat rather well to match.

As this was my second build and I was slowly becoming more comfortable with 3D-printed parts, I decided to use a hybrid of printed parts, off-the-shelf parts and hand-cut parts. It has a perforated ABS chassis, printed Nylon side-armor, and cut HDPE front-armor mounted on shock-absorbing TPU standoffs.

This approach has its pros and cons. Cut and injection-molded parts are generally stronger than 3D-printed ones, and perforated parts save a significant amount of weight. However, a fully 3D printed chassis requires fewer (weight-costly) screws and fixtures, and less manual labor overall. Everything is a balance.

The weapon flywheel was more of a cost compromise than a weight compromise. A metal cast weapon of this shape would be expensive to purchase, and so I went with a TPU print with steel impactors and brass inserts to make up for the weight. It weighs 14 grams in total, which is small by Antweight standards, but still enough to flip and damage an opposing robot.

At the time of writing, Compromise has a record of 4 and 4 in its combat outings. I’ll hope to have some build and competition videos compiled soon.






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