RM Hub Motor V3

This post covers the background, development, manufacturing, and reflection on the third generation of my 1lb commercial combat robotics hub motor. This motors marks the greatest departure and improvements from previous generations. Fully custom stators and magnet rings improve peak output power from 200W to 320W. 35% larger bearings improve durability far beyond any market competitors. Active cooling channels aid heat dissipation and enable cryogenic cooling. Lastly, an updated architecture improved reliability while reducing costs by 64%. In testing, the motor and associated robots performed exceptionally well, winning multiple competitions and placing top 6 in thge world championships. 

Combat robotics is an emerging sport in which two opposing robots attempt to disable one another. Over time, dominant competitive strategies have led to the prevalence of several distinct archetypes. Among these, robots equipped with rotary weapons have become the most consistently effective. These systems, commonly referred to as spinners, provide a comparatively simple and efficient means of storing and releasing kinetic energy for damaging an opponent.

Although the underlying principles of spinner weapons are relatively simple, the extreme forces involved require consideration. A weapon "blade" must be spun to high speeds, typically in excess of 30k rpm, and withstand the reaction forces of coming to a complete stop in an instant on impact. In addition, weapons are often used in a defensive manner, resisting off-plane impacts from opposing robots. To address these constraints, I previously designed two generations of custom hub motors for 1lb robots. The first generation effectively demonstrated the potential of the concept, winning multiple competitions and never failing in combat. Despite these successes, the design was a rapid prototype and had a number of shortcomings. It carried some excess weight and had limited servicability. 

The second generation of motor attempted to resolve these issues through a number of notable improvements. Critically, it introduced the innovative concept of swappable stators to rapidly change the configuration of the motor to suit different applications. This motor was an incredible success, selling all produced units and powering multiple robots to over 10 podium finishes. Unfortunately, this motor still had room for improvements. The manufacturing process required the stator and rotor to be cut from a pre-existing OTS drone motor. In addition, repeated impacts occasionally caused the bearing shields and bearing spacers to be ejected, resulting in the motor jamming. Lastly, the central post on which the stator was mounted was a complicated part which required multiple setups to fabricate.  The third generation RM Hub Motor attempts to solve all these issues through a complete architectural overhaul.

The following design goals were placed for the design of the motor.

Durability- Improve upon the previous generation and eliminate any potential weak points

Performance-Increase power and startup torque to aid in self-righting and weapon spinup

Cooling- Integrate cooling solutions to enable sustained maximum output for the duration of a match

Manufacturability- Minimal manual assembly required. All custom components

Weight- Lighter than all other market competitors

As compared to the previous generation, the rotor size was dramatically increased. This resulted in a larger overall footprint which required a more aggressive weight reduction to hit the target values. To compensate for the decreased cross-sectional area, the outer material was changed to be 7075 aluminum. The new design eliminates a critical weak point from previous designs; a thin lip that the bearing race sits on. This means that in the event of an extreme lateral impact, it will not shear and fail. 

Despite the larger size and increased strength of the outer shell, the weight was reduced by 12% as compared to V2. This also reduced the overall moment of inertia, further reducing spinup times. 

Convective cooling channels were milled into each base, allowing hot air to escape and improve heat dissipation. In addition, the ports reduce material and thus weight. By integrating slots into the mounting structure, liquid gas (computer duster) can be sprayed directly into the stator windings before each match. This cryogenically cools the motor down below -70C improving performance. 

Currently, five prototypes have been produced and were tested on my 1lb champion robot "Biolumuminescent". In the three competitions that it has been used in, my robot performed exceptionally well with two first places and placing 6th out of over 500 robots in the world championships. The motor currently has the best torque, power/weight ratio, and durability out of every weapon system currently availble. It was able to withstand repeated impacts from robots in higher weight classes, demonstrating its exceptional reliability. 

When the motor is combined with the weapon disks designed by my SIMP topology optimizer for combat robot weapons, it demonstrates near unparalleled destructive capability. Nearly every opponent that has been hit, has been irreparably damaged and retired. Below is a small selection of robots after fights.

Overall, this revision of the motor is a resounding success. It has exceeded all expectations set forth and has powered my robots to victory after victory. I am receiving extremely high demand for this motor and have put in an order for 100 units by the end of the first 2026 quarter.