1/16/2026 Taylor Parks
Written by Taylor Parks
While it isn’t false to say that mechanical engineering seniors Vaatsalya Aiyer, Aidan Dempsey, Matthew Martin, Matthew Springer, and James Weiland’s capstone design project involved playing with toys, the true extent of their efforts goes much further.
The team focused on designing a bristle bot that can outperform its commercially available rivals while costing significantly less to manufacture—which can enable more effective active matter experiments.
In robotics, the term “bristle bot” refers to a class of small (i.e., the head of a toothbrush) walking robots that use bristles as legs. These bots each contain an eccentric rotating mass vibration motor, which rotates a shaft affixed with an uneven weight to produce vibration. Bristle bots can be designed with uneven center of mass and soft legs so that the vibration produced by the motor results in net forward movement.
“We use these robots to study how collections of active, self-propelled bots interact with soft, deformable boundaries, and how such interactions can lead to guided locomotion of the entire confined system,” said Assistant Professor and project sponsor Varda Hagh.
The coupling of an active particle with a soft boundary can be demonstrated by placing a single bristle bot within a circular, closed paper fence on a flat table. Once activated, the bristle bot will move forward until it contacts the paper enclosure. It will then move along the paper like a train on a track. Because the paper is not attached to the table, it will experience motion in reaction to the forces applied by the bristle bot, resulting in a coupled bot-and-paper system whose net motion is influenced by the characteristics of the paper and velocity of the bristle bot. Add more bristle bots to the enclosure, and the resulting movement of the boundary will increase.
“If you allow [active particles] to move on their own, they will randomly diffuse,” Hagh said. “By confining them within a boundary, you can harness their movement to solve complex problems and have the system navigate a landscape without getting diffused or lost.”
Bristle bots are more widely recognized as educational toys, with the HEXBUG brand a common name in the market. However, these options are not well-suited for active matter experimentation, as they are relatively expensive to buy in bulk and cannot be exposed to wet or harsh environments due to their lack of sealed electronics.
“There are a number of issues with current bristle bots, like the HEXBUG,” Weiland said. “Most notably, you can’t take the battery out to maintain it easily, it takes time to ship when ordered online, and the motion is inconsistent. Our design addresses those limitations.”
The team developed a comparably sized bristle bot with two batteries and one motor contained within a 3D-printed chassis. The chassis can be fitted with modular polylactic acid (PLA) filament legs to allow for easy customization of leg number and geometry.
“This allows us to systematically study how these features affect locomotion,” Hagh said.
The team’s prototype costs approximately $2.80 to print, or less than half of the commercial cost of one HEXBUG toy.
“Once we did our initial analysis of [existing bristle bot design], we prioritized rapid prototyping to see what worked and what didn’t,” Weiland said. “We’re in the triple digits for the sets of legs we’ve printed.”
“We did a lot of materials testing for the legs as well,” said Dempsey, noting that the team had experimented with thermoplastic polyurethane (TPU) filament as well as multiple thicknesses of laser-cut rubber before proceeding with PLA. They also made modifications to the chassis for easier manual assembly.
“If you look at the internals of the commercially available bots, everything is super tight together, and that level of assembly would be really hard to achieve by hand,” Martin said.
“We actually put in a little extra space near the motor and switch so that you could fit everything in using your hands,” Springer said.
For these seniors, all of whom will graduate in May 2026, the bristle bot’s manufacturability, scale, and motion were all welcome opportunities to apply their engineering skills in new ways.
“We did a lot of hands-on work with iteration and prototyping, and we were able to see what works and what doesn’t really quickly,” said Springer, who intends to take an industry position focused on finite element analysis after graduation.
“It’s not a major investment to make one of these, so it was really awesome to be able to get such quick feedback on any hypothesis you have,” added Weiland, who plans to do data analysis for McKinsey & Company.
“In all the design courses in mechanical engineering, you’re working with larger robots or larger cars, and this is much smaller,” said Dempsey, who plans to work for Constellation Energy. “We could only print [chassis] walls as thin as the [printer’s] nozzle diameter, and you’d never consider that in your other projects.”
“I think the mechanism of motion with the vibration was very different than anything we’ve learned in our classes, and that was really cool to explore,” said Martin, who will also be going into nuclear power with Enercon.
“Troubleshooting was also really interesting because there was bias present in the motion throughout the semester and reducing that bias was part of solving the problem,” added Aiyer, who will be performing simulations and conducting crash tests for Ford Motor Company.
“A group of undergraduate students in our lab are working on this project and will further develop the design based on the ME 470 group project,” Hagh said of next steps. “A graduate student will use the resulting bots in his scientific experiments.”