Design Problem

In Kenya, Mkokoteni carts are vital for transporting goods but face challenges like road blockage, strain on pushers, accidents, and animal cruelty. An innovative solution, a spring-powered design inspired by toy cars, aims to alleviate these issues. Harnessing downhill energy assists uphill movement, reducing strain on pushers and enhancing road safety. While electric models offer advanced features, the focus remains on cost-effective solutions to improve the livelihoods of cart operators.

Design Process



  • Problem: Traditional Mkokoteni carts in Kenya contribute to traffic congestion, physical strain on pushers, safety concerns, and potential animal cruelty.
  • Solution: A spring-powered Mkokoteni cart design.
  • Reason for the problem: Mkokoteni carts are slow, require manual effort, lack efficient brakes, and sometimes rely on animal traction.
  • Reason for the solution: The spring-powered design addresses these shortcomings by storing energy during downhill movement to assist uphill propulsion, improving control mechanisms, and eliminating the need for animal traction.
  • Affected by the problem: Mkokoteni cart pushers (physical strain, safety risks), other road users (traffic congestion, safety), and animals (potential cruelty).
  • Benefits from the solution: Reduced physical strain and safer operation for Mkokoteni cart pushers, improved traffic flow and safety for other road users, and elimination of animal cruelty.


  • Mkokoteni Cart: A hand-pushed cart used in Kenya to transport goods, durable but presenting challenges such as road blockage, physical strain, accidents, injuries, and safety issues for the pushers and animals.
  • Objective: To alleviate these issues through a spring-powered design, making the carts more efficient and user-friendly. This design will reduce physical strain, improve road safety, and eliminate the need for animal traction.



  • Inspiration: The design is inspired by the mechanics of a toy pull-back car, utilizing a spring to store and release energy:
  • Mechanism: Detailed exploration of toy pull-back car mechanisms and the development of a reverse gear mechanism to keep the cart moving forward.
  • Challenges: Modifying the pull-back mechanism to wind up the spring without the need to pull back, and designing a locking mechanism for practical use in a larger scale.


  • Initial Prototypes: Creation of models using Lego to replicate the reverse gear mechanism and explore the functionality of the spring and locking mechanisms.
  • Version 1
  • Version 2:
  • 3D CAD Model: Developing a compact gearbox design that includes a neutral position and a locking mechanism, to be laser cut out of acrylic for initial prototyping.



  • Materials for Prototype 1: Acrylic, 3D printing filament, wood.
  • Materials for Final Prototype: Metal fabrication.
  • Steps: Laser cut parts from the 3D model, 3D print necessary components, assemble, and test. Identify and address any issues for further refinement.


  • Prototypes: Fabricate prototypes using laser cutting and 3D printing to test the design in real-world conditions.
  • Objectives: Ensure all components work together harmoniously, identify necessary modifications, and improve the design based on test results.



  • Prototype Testing: The initial acrylic prototype faced several issues, including the fork not moving the small gear properly, excessive friction between gears, instability of the shafts, and alignment issues between the locking gear and the fork.
  • User Testing: Gather feedback on usability, performance under various conditions, reliability, and compatibility with other systems. Document any technical issues and user feedback.


Redesign: Address identified issues by:

  • Redesigning the fork for better contact with the gear.
  • Increasing the size of gear teeth to reduce friction.
  • Adding specific rings to control the shaft positions.
  • 3D printing the fork and locking mechanism as a single piece for accurate alignment.
  • Iterative Testing: Continuously test and refine the prototypes to enhance performance, functionality, and user satisfaction until the final product meets all desired specifications and expectations.

Link to Process Journal and Final Reflection Video