The Evolution of DarkHorse - From Terrible to Terrifying

This is the design story of DarkHorse — a wide vertical spinner built for the RPI Combat Robotics Tournament. It began life as a concept called The Moderator, and has now reached its third major iteration. The path from the first CAD model to the current V3 architecture is a story of constraint-driven redesign, mass management, and learning what actually survives in the antweight arena.

1. The Original Concept: The Moderator

In early 2026, the first complete concept took shape: a wide, low, red-framed vertical spinner with a distinctive curved blade and prominent front forks. The robot was named The Moderator, a tongue-in-cheek reference to the idea of “moderating” the competition by removing opponents from the arena. The CAD model and four-view schematic were locked on 7 April 2026.

Figure 1 — Early render of The Moderator (red chassis, gray curved blade)

The architecture already contained many of the ideas that would survive into DarkHorse: a wide stance for stability, a vertical spinner for high kinetic energy, and aggressive front geometry intended to control engagement. The blade itself (internaly called “spinny boi”) was a single-piece curved design whose mass properties were measured at 0.139 lb (~63 g) in CAD.

Figure 2 — Official four-view schematic of The Moderator, 7 April 2026 (THATCONORGUY)

2. Reality Check: Mass, Materials, and the 1 lb Limit

The first complete mass budget for The Moderator came in overweight. Early estimates put the robot well over the 453.6 g (1 lb) hard limit that defines the antweight class at RPI. The polycarbonate armor, multi-piece chassis, N20-class drive motors, and heavier battery solutions that felt “safe” on paper simply did not leave enough margin for a competitive weapon system.

This forced the first major redesign. The curved “spinny boi” blade was replaced by a simpler, thicker AR-500 disc geometry that could be cut more reliably and still deliver high tip speed. The chassis philosophy shifted from a rigid multi-piece structure toward a single flexible TPU body that could absorb impacts while remaining printable in one piece. Drive motors were upgraded from N20s to the more powerful Repeat Robotics 16 mm brushed planetary units. These changes marked the transition from “The Moderator” as a concept into DarkHorse as a buildable robot.

Figure 3 — Mass properties of the original “spinny boi” blade (0.139 lb / ~63 g)

3. Becoming DarkHorse — The Second Iteration

The name change was deliberate. “The Moderator” had been a playful working title; DarkHorse better captured the intent of an understated, high-performance vertical spinner that could surprise more established designs. Visually the robot moved from the bright red of the original renders to a blue/black TPU aesthetic with “DARK HORSE” lettering integrated into the frame. (Fun Fact: The "DarkHorse" name and color way was partally inspired by the Ford Mustang Dark Horse!)

Key architectural decisions solidified in this phase:

• Weapon: Direct-drive hub motor (Just Cuz RDY-MINI-5022-V2 1700 KV) mounted to a 1/8" AR-500 blade (eventually finalized at 127 mm OD).

• Chassis: Unibody 95A TPU frame with integrated front forks/armor zones. The flexible material was chosen specifically for energy absorption and rapid, low-cost replacement after a fight.

• Drive: 2WD using Repeat Robotics 16 mm brushed planetary motors and custom-cast silicone wheels.

• Power: Migration toward a single 4S 450 mAh pack for better power-to-weight than earlier dual-2S or higher-capacity solutions.

By the end of the second iteration the robot was recognizably DarkHorse, but mass was still a constant negotiation. Several early BOM revisions still showed the robot slightly overweight or with almost no remaining margin.

4. The Third Iteration (V3) — Closing the Gaps

V3 is the current, competition-intent design. The focus shifted from “does the concept work?” to “does every gram earn its place, and can the robot be repaired between fights?”

Major V3 refinements:

Chassis & Armor — Fully committed to the unibody 95A TPU frame (~98 g). The multi-piece + polycarbonate approach was abandoned. A printed PETG-GF top plate (~19 g) replaced sheet polycarbonate, saving weight and simplifying assembly.

Weapon — 1/8" 127 mm AR-500 blade (~88–91 g) driven by the Just Cuz RDY-MINI hub motor (72.5 g). Theoretical no-load tip speed exceeds 370 mph; realistic combat tip speed is estimated around 300 mph with stored energy in the high hundreds of joules — extremely high for a 1 lb robot.

Drive — Repeat Robotics 16 mm brushed planetary motors retained. Drive ESC finalized as the Weka dual brushed ESC (20 A per channel) after evaluating the Dominion unit. Custom silicone wheels for traction and shock isolation.

Power — Single OVONIC 4S 450 mAh pack (~51 g). The dual-2S series arrangement and heavier packs were dropped to reclaim critical mass.

Electronics — RadioMaster eLRS receiver, 45 A BLHeli weapon ESC, Just Cuz power switch. Total electronics + wiring kept deliberately light.

The net result is a robot that sits under the 1 lb limit with a small but usable remaining margin (on the order of a few grams depending on final hardware choices). The design is now locked on the major subsystems; remaining work is final feed-fork geometry, physical CG confirmation, and fight-specific configuration options.

Figure 4 — DarkHorse V3.0 hero shot (current competition design)

5. Design Philosophy That Survived Every Revision

Across three iterations a consistent set of priorities emerged:

Energy absorption over pure rigidity. The TPU unibody is intended to deform in a controlled way, protecting the hub motor, ESCs, and battery.

Rapid repair between fights. A single printable chassis and modular forks mean the robot can return to the arena after a destructive match without waiting for complex fabrication.

Concentrate mass in the weapon. Every gram saved in the chassis, top plate, and drive system is a gram that can live in the AR-500 blade or the hub motor.

Direct-drive simplicity. No belts, no gears in the weapon path. The hub motor is the weapon mount.

6. Looking Ahead

DarkHorse V3 is the first version that feels ready for the RPI Combat Robotics Tournament at the end of the semester. The major subsystems are selected, the mass budget is under control, and the design language (blue/black TPU, wide vertical spinner, front forks) is settled.

What remains is the work that only physical testing can answer: final CG location, fork geometry under real impact loads, and the inevitable last-gram optimizations that appear once the robot is fully assembled and weighed on a scale. The design story is not finished — it simply has a clear next chapter.

From a red-framed concept called The Moderator to a blue unibody vertical spinner called DarkHorse, the robot has been continuously rewritten by the same constraint that defines the class: one pound. Everything else, the blade, the motors, the frame material, even the name, adapted around that number.

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