Surly Big Dummy "Mr.Dummy" with V3 Rear All Axle

The Mr. Dummy Build was designed around the goal of creating a powerful, reliable, and serviceable electric cargo bike capable of hauling heavy loads while maintaining the ride characteristics of a traditional long-tail bicycle.

The foundation of the build is a Surly Big Dummy cargo bike equipped with a Grin Technologies Rear All-Axle Hub Motor integrated into a custom-built rear wheel. The All-Axle system was selected because of its exceptional torque handling, regenerative braking capability, and compatibility with modern cargo-bike applications.

The system uses a 48V battery platform paired with a Cycle Analyst V3 (CA3) for advanced programming and ride customization. The CA3 allows precise adjustment of power output, regenerative braking, speed limits, and pedal-assist behavior.

Unlike many aftermarket conversion systems that rely on cadence sensors, this build incorporates integrated torque sensing, allowing the motor to respond proportionally to rider input. This creates a more natural riding experience while improving efficiency and battery management.

One of the most important features of the Mr. Dummy Build is regenerative braking, which returns energy to the battery during deceleration while simultaneously reducing mechanical brake wear. This feature is particularly beneficial on a cargo bike carrying heavy loads.

Key features include:

Surly Big Dummy long-tail cargo bicycle

Grin Technologies Rear All-Axle Hub Motor

Custom-built rear wheel

48V battery system

Cycle Analyst V3 programmable display

Integrated torque-sensing pedal assist

Regenerative braking

Fully programmable power and speed settings

Designed for heavy-duty cargo and utility applications

The completed system provides significantly more hauling capability than a conventional bicycle while preserving the flexibility, serviceability, and customization advantages of an open-source electric drive system.