ARCC 2026 Infantry Robot

Project Overview

Competition rules limited the Infantry robot to 300 Wh of total power capacity, a maximum supply voltage of 30 V, a maximum mass of 25 kg, a 600 × 600 × 600 mm storage envelope, and an 800 × 800 × 800 mm maximum transformation envelope. A supercapacitor system was permitted with up to 2000 J nominal and 2200 J measured energy storage. The Infantry also had to carry a single 17 mm launching mechanism and approximately 3.25 kg of referee-system hardware, including four armor modules, a projectile-speed monitor, video transmitter, field-interaction and positioning modules, and power and control electronics, several of which imposed defined mounting and keep-out requirements.

The chassis frame was built from straight and bent 1 × 1 in aluminum extrusions joined through laser-cut aluminum brackets. Above the aluminum frame, an additional interlocking carbon-fiber structure housed all four swerve-suspension modules. Machined aluminum strips with mutually perpendicular M4 tapped holes joined the carbon- fiber plates, while a main plate approximately 450 × 450 mm supported the gimbal bearing and tied the turret directly into the chassis structure. Components with more complex geometry—including swerve bearing couplers, steering-torque transmitters, ammunition channels, the feed tube, and protective shields—were 3D printed in PLA, PA6-CF, or TPU depending on their mechanical requirements.

My Contribution

Planned referee-system component placement and designed mounting and protection hardware for electronics.
Sourced new reduction gearboxes and traction wheels with larger bores to simplify the drivetrain design and raise the chassis' maximum speed.
Completed the full two-iteration mechanical design process for the suspension swerve chassis.
Developed MATLAB models and simulated suspension response to multiple terrain inputs.
Designed TPU shields around the swerve and suspension systems using multi-profile, guide-curve lofts to protect the modules from projectile impacts.

Interactive CAD Model

Explore the complete mechanical assembly and its major chassis, suspension, gimbal, and turret subsystems.

View ARCC 2026 Infantry on Onshape →

Interactive model of the ARCC 2026 Infantry Robot. Drag to rotate, scroll to zoom, and right-click or two-finger drag to pan.

Chassis Development

After RMNA 2025, the team recognized that suspension was important for maintaining traction during aggressive maneuvers and reducing vibration when the robot crossed uneven field surfaces or ammunition scattered on the ground. Although X-drive offered substantially greater mechanical simplicity, we still valued the traction and translational performance of swerve drive. In one match, our previous swerve robot pushed a disabled opponent X-drive robot out of a capture point with little difficulty. The reverse situation also mattered: a disabled swerve robot is difficult for the predominantly X-drive field to push. We therefore decided to preserve this push-and-resist capability for unexpected match situations while adding suspension.

Among open-source suspension-swerve designs in the ARCC/RoboMaster community, two common suspension-travel mechanisms were four-bar linkages and vertical linear guides that move the entire swerve module—including both steering and drive motors. The latter is often referred to by the community as an "over-the-ring" suspension because the steering motor is commonly a DJI GM6020 with a central through-bore that allows a slip ring to pass through.

Suspension swerve concept placeholder image 1 — "Over-the-ring" suspension for swerve with external linear guide rails.

Suspension swerve concept placeholder image 2 — "Over-the-ring" suspension for swerve with four-bar linkage.

Suspension swerve concept placeholder image 3 — Sliprings donated by JINPAT Electronics.

Because a faster-spinning chassis reduces the time each armor plate remains exposed to incoming fire, the swerve modules should be packaged as close to the robot center as practical to reduce rotational inertia and enable higher angular acceleration and speed. The conventional suspension layouts were not as compact as an "under-the-ring" arrangement envisioned by our team, in which only the wheel and drive motor travel vertically while the steering motor remains rigidly connected to the chassis.

Under-the-ring swerve placeholder image 1 — Prototype swerve module in Nov 2025.

Under-the-ring swerve placeholder image 2 — Fully built prototype swerve chassis.

Under-the-ring swerve placeholder image 3 — Prototype full infantry with turret in Dec 2025.

With most of the team's budget allocated to computing and vision hardware, new motors and wheels, and other custom parts with more direct performance impact, the suspension system and new motor-gearbox-wheel assembly had to fit inside four existing cross-roller bearings with 120 mm inner diameters. These bearings were too small to surround the wheel at its axle as in our previous swerve designs. I therefore designed a PA6-CF bearing coupler that fit inside each bearing and supported the vertical guide and suspension strut. A central opening allowed a box made from carbon-fiber plates—containing the drive motor, wheel, and wheel bearing—to travel vertically while retaining adequate wall thickness around the coupler. I also accounted for dimensional change and resulting clearance shifts after annealing. Above this assembly, a bridge-like torque transmitter connected the fixed steering motor to the traveling submodule while leaving sufficient room for suspension motion below it.

Simulation of the Suspension Swerve Chassis

I was taking ME 3017—System Dynamics—while designing the chassis. The main course project was to analyze an interesting and sufficiently complicated real-life dynamical system, and this chassis, modeled as a four-corner spring-mass-damper system, was a natural fit. I teamed up with two classmates to develop a 7-degree-of-freedom vehicle model consisting of chassis heave, roll, and pitch plus the vertical motion of the four individual swerve modules. Each corner was modeled with suspension stiffness and damping between the chassis and wheel assembly, while the tires provided an additional stiffness-and-damping interface between the wheels and terrain.

We first developed a linear state-space model using a rigid chassis, small-angle roll and pitch assumptions, identical suspension corners, and purely vertical wheel motion. We then expanded it into a nonlinear model that retained the exact trigonometric relationships between chassis roll, pitch, and corner height and allowed nonlinear tire stiffness to be represented with a cubic stiffness term. The resulting system contained seven coupled second-order differential equations, or 14 first-order states when positions and velocities were represented separately.

We implemented both models in MATLAB and simulated the chassis against several terrain inputs: a 30 mm single-wheel bump, opposing sinusoidal inputs to excite chassis roll, and randomized rough terrain with rear-wheel inputs delayed according to wheelbase and vehicle speed. The simulations tracked chassis heave, roll, and pitch, individual wheel displacement, suspension travel, and normal wheel loads, allowing the linearized and nonlinear models to be compared under the same categories of disturbance. The linear model was useful for describing the fundamental suspension response, while the nonlinear model better represented larger disturbances where geometric effects and changing tire stiffness became more significant.

Swerve suspension simulation placeholder image 1 — Generalized chassis response to 3 different types of terrain input.

Swerve suspension simulation placeholder image 2 — Generalized and individual module responses to a step input.

Swerve suspension simulation placeholder image 3 — Responses to random input (note the magnitudes).

The first iteration of the swerve module used linear guide rails and carriages as the suspension-travel mechanism. During a design review with the team's founder, however, I was convinced that the rails and their recirculating-ball carriages could be vulnerable to impact, contamination, or small deformations. A linear-bearing-and-guide-rod arrangement offered a simpler and more robust substitute, so I incorporated it into the second iteration by modifying the bearing coupler.

Swerve module first iteration placeholder image 1 — Infantry in Apr 2026 (note the linear guide rails had been replaced).

Swerve module first iteration placeholder image 2 — Infantry during tech assessment Apr 2026 (from another angle)

Swerve module second iteration placeholder image — Behind the swerve module shield (had to keep #nodes the same so the geometry wouldn't twist).

Each swerve module was housed within two side plates set at 90 degrees and a top plate carrying the steering motor. Initially, each cross-roller bearing was to be supported by an individual gusset plate between the side plates. I then noticed that the turret's cross-roller bearing sat at a similar height and merged the four separate bearing plates with the octagonal gimbal-bearing plate. The result was a single major carbon-fiber structural plate approximately 450 × 450 mm. Aluminum strip connectors were added wherever major plates intersected, joining them with bolts and creating an exceptionally rigid chassis-gimbal framework by competition-robot standards. All carbon fiber plates on this robot (including the big one) cost only 2000 CNY ($300) and took 3 days from quoted to shipped.

Infantry chassis structure placeholder image 1 — The main carbon fiber plate isolated in context of the chassis frame.

Infantry chassis structure placeholder image 2 — A closer look at a housed prototype swerve module and its connections.

Infantry chassis structure placeholder image 3 — Threaded aluminum strips used to build the chassis, ￥4.9 ($0.7) each.

Turret Development

This robot shared the same general turret architecture as the ARCC 2026 Sentry Robot → . The Infantry used a different computing unit, however, so its ammunition storage was reshaped around the available electronics package, and it did not require the spatial- memory module mounted on the Sentry.

Infantry turret placeholder image 1 — Infantry turret assembly screenshot (with latest protection).

Infantry turret placeholder image 2 — Infantry test fire target setup (its own armor plate, 10cm x 10cm) and dispersion.

Infantry turret placeholder image 3 — Trying to figure out how much torque was needed to pitch the gun.

Development Video

Development footage showing suspension travel, swerve steering, chassis motion, and subsystem testing before competition.

Infantry chassis development and testing footage.

Competition Video

Match footage of the Infantry robot competing in 1v1 and 3v3 at ARCC 2026.

ARCC 2026 Infantry competition footage.

Lessons Learned

The main problem with this chassis was weight. A swerve drivetrain inherently required four additional steering motors—roughly 600 g each with the DJI GM6020—but there was still substantial room for structural weight reduction. Several carbon-fiber components were thicker than necessary; for example, some 5 mm swerve top plates retained nearly their full profile because we were concerned about projectile impacts. The TPU shields were extremely tough and effectively indestructible under 42 mm hits, but four sets of shields still added roughly 800 g even with only two wall loops and 10% infill. The improvised steel mesh used during competition worked, but a future version needs a purpose-designed lightweight protection system.

Evaluation of the suspension was mostly qualitative. If the pilot reported that traction remained consistent and the vision system stayed clear, we considered the system successful. Adding a chassis IMU and position sensors to each suspension would produce better data, but it would also add electrical and software integration work with limited competitive benchmarking value. From observation and pilot feedback, the final setup still appeared somewhat stiff, so the team planned to test softer springs in future iterations.

The turret carried many of the same limitations discussed on the ARCC 2026 Sentry Robot → page. Implementing a bottom-feed ammunition architecture would require even more careful packaging on the Infantry, because the swerve modules occupy substantially more chassis volume than the Sentry's X-drive modules.