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Design of an Assistive Tricycle

This project aims to design a tricycle to be used by persons with lower-limb disabilities who possess full function in only one leg. To achieve this, specific criteria were established for the tricycle’s design:

  1. Enable single-leg pedaling at a speed of 12kmph.

  2. Maintain affordability and durability.

  3. Facilitate easy assembly and repair at standard bicycle repair shops.

  4. Ensure narrow dimensions for maneuverability in small streets.

  5. Withstand bumps and potholes commonly encountered on Indian roads.

Design Ming Map

Following a design flowchart analysis, it was determined that the pedaling mechanism design was of utmost importance.

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Utilizing existing Indian anthropometric data and user studies, the maximum knee force and range of motion were determined. Traditional circular sprocket designs were found to exceed the knee's range of motion (ROM), potentially causing discomfort. To mitigate this issue, an elliptical pedaling mechanism employing a four-bar mechanism was devised.

Circular Mechanism Knee Angle Range
Elliptical Mechanism Knee Angle Range

Knee ROM with a circular sprocket mechanism

Knee ROM with the proposed elliptical mechanism

Through a grid-search optimization process, link lengths for the four-bar mechanism were fine-tuned while adhering to Grashof's criterion. Ultimately, a sprocket ratio of 2 was chosen, reducing the required force to acceptable levels. Despite a slightly faster cadence compared to circular mechanisms, it remained within user study parameters.

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Moreover, it was discovered that knee range of motion depended not only on seat height but also on horizontal seat position. To accommodate a wide range of users, a dual adjustable seat was developed.

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Given the single-leg pedaling limitation, a flywheel was integrated into the pedaling mechanism to release stored energy during the latter half of the pedaling cycle.

Safety was ensured through ANSYS FEA simulations, subjecting all components to fatigue, 3g bump, and 2g torsional loading. Subsequently, all parts were assembled using Autodesk Inventor, and production and assembly drawings were prepared

FEA of the frame in 3g bump loading
FEA of the frame in static loading
FEA of the frame in 2g torsional loading

Deformation of the frame under static (left), 3g bump (center) and 2g torsional loading (right) respectively

FEA of the Rear Sprocket Adapter - Deformation
FEA of the Rear Sprocket Adapter - Stress

Deformation and stress on the rear sprocket adapter. The sprocket adapter performs three functions - it acts as a rear brake rotor, it transmits power from the rear sprocket to the driveshafts and also acts as a flywheel . 

Read the full report below:

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