The Shop 'n Cart

To a much more dramatic, complete account of how Shop 'n Cart preformed at the contest (worth reading, I hope you think so too)

The Shop 'n Cart project was built with my high school engineering team my junior year of high school (1993). It was for the National Engineering Design Challenge (NEDC).

The problem we had to solve was the following: A person who handicapped has to remove 120 lbs. of groceries from their car and get them in to there house. The four bags of groceries have to be removed from a simulated car truck carried across a pile of wood chips, up a ramp, down 3 stairs, back up the three stairs, and back down the ramp. The operator could exert NO MORE THEN 7 lbs. of force on the machine.

We built a giant motorized cart. The cart (called Shop 'n Cart) had two main parts. The lower (more complicated part) had the drive train, control circuits, and power supply. The upper half removed the groceries from the car and held them in place while the cart was in motion.

Research

We went and visited the Prince George's County Maryland Fire Department's Bomb Disposal Robot to get ideas for the different ways we could build our machine.

The Lower Half

The only power tools use to build the lower half was a drill and a soldiering iron. The structural elements were make of zinc angle iron with lots of predrilled hole in it (usually used for shelving). The power supply was a wheel chair battery. The four drive motors were from power wheel kiddy cars. The gears and drive chains were from roll up fire doors. The wheel were 20 inch BMX bicycle wheels.

Below is a drawing of the final drive train assemble. There were Two previous versions before we built this one. The chair drive provides a 7:1 mechanical advantage, from the motors to the wheels.

Below are copies of some of the early conceptual sketches various members of the Team came up with early in the design process.