Abstract

The objective of this project was to build a machine capable of climbing stairs. The machine called “Sojourner” was built to meet the requirements of “Bulk Material transporter” student design contest organized by the ASME. The structure of the machine was based on the Tri-wheel configuration patented on October 24th, 1967 by Robert W. Forsyth and John W. Forsyth, assignors to Lockheed Aircraft Corporation, California, USA. The transporter is driven by four sets of wheels - two tri-wheels in the front and two normal circular wheels at the rear.

Tri-wheels here refer to a system of three wheels sandwiched between two Y-frames. This design allows for two kinds of motion of the wheels of the tri-wheel system – first, about the axis through the centre of each of the wheels and second, the rotatory motion about the axis of the tri-wheel system itself. This flexibility empowers he transporter to climb steps easily. A well functioning prototype has been designed and manufactured in our lab. This transporter is able to passively overcome unstructured obstacles and climb steps (more specifically) up to 12 cm in height.

One of the most important constraints was to fit the entire machine within a given volume of 30 cm*25 cm*25 cm. In order to accommodate constraint, we could provide the triwheel system on the front of the transporter only. A machine with tri-wheel systems replacing all four conventional wheels of a four-wheeled car provides an ideal demonstration of this concept. The entire project was funded by Umesh Mashruwala Innovation Cell (UMIC), IIT Bombay.

The functional part of this design is the tri-wheel system replacing the conventional front wheels of a car. Each Triwheel system comprises of three wheels of diameter 10 cm and two Y-frames, each with an arm length of 12 cm. The wheels are mounted onto the frames at a distance of 6.67 cm from the centre of the Y. The frames basically function as supports sandwiching the wheels between them. A sunplanet system of gears is provided in order to drive the wheels of a tri-wheel system. The sun-planet arrangement ensures equal torque transmission to each of the wheel while also forcing them to rotate in the same direction with equal rpms.

The unique feature of the design is that the wheels can rotate independent of the motion of the entire triwheel system as such. The design also has provision for rotation of the entire tri-wheel system. The rear wheels are ordinary circular wheels with diameter of 10 cm. Their main function is to provide support to the triwheel and also an up thrust to the entire vehicle during
ascent over the stairs..

Project Done by Kaushik & Ankit Mehta

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