Edem Adzo Diaba

Frank Anamuah-Koufie



The objective of the task was design a system of machines capable of moving a small ball (6cm diameter) across a distance of one metre into a goal area. The goal area has dimensions 25cm X 25cm X 10cm. the mechanism is designed to be touched once and be “automated” for the rest of its course.


The following constraints affected the design of the machine:

  1. The machine must be composed of locally acquired materials only.
  2. Materials purchased in building the machine should not cost more than GHC20.00.
  3. The machine must be composed of a minimum of four simple machines.
  4. The machine may only be touched once, the purpose of which is to get it started.

The constraints listed above naturally limited the options we had in designing a solution. However, it also paved way for creativity and new thoughts about possible uses of some materials that were considered to be waste materials or would have never been considered in the building of mechanical systems.


We pictured the machine in terms of the stages involved in accomplishing the task. These were:

  1. Picking up the ball
  2. Moving the ball across the distance
  3. Dropping the ball in the goal area

In picking up the ball, we considered several options that included having an arm attach a metallic tape to the ball and picking the ball up with an attached magnet. We also came up with a “dustpan and broom” mechanism that would “sweep” the ball from the floor unto a “launch pad”.

 We considered three possibilities for moving the ball across the distance. The first option was to “fly” the ball using a catapult or lever mechanism from the machine directly into the box. The second consideration involved rolling the ball on the ground from an inclined plane straight into the box. But this was based on a misconceived idea that the goal area would have a front-facing opening rather than the upward-facing opening it had. Our final consideration was to have the ball drop from a height and then bounce into the box in a calculated number steps.

One option for dropping the ball required actively dropping the ball into the goal area by turning of an electromagnet that would be mounted on an arm carrying the ball across. The other options were simply passive results of the “moving process” and as such would not require a deliberate attempt to drop the ball.

Each of the three steps were tested independently to ascertain their efficacy before being tested together to see how the whole system may work.


We chose to use an iterative process in building the machine. The steps involved were designing, building and testing in that cycle respectively. We began with 2 days of brainstorming and sketching our initial ideas on paper. At this stage, we considered no physical limitations and allowed all sorts of ideas to flow.

The next step, which involved building models, was more realistic. At this stage, we focused more on the physical challenges that the machine may face. We considered weight limitations, material limitations and the role certain forces such as gravity and friction would play on the functioning of our machine.

Our first model involved 3 simple machines; a pulley to release a calculated weight onto an inclined plane. The weight would then slide down the plane and gather momentum enough to catapult the ball from one end of a simple lever into the goal area.

Our tests revealed a number of challenges and provided some new insights into building the machine. We realized that using a stone as our weight was difficult because we could not control the weight and it was also difficult to get the ball rolling on the inclined plane. Another challenge we encountered was getting the pulley to support two heavy stones. Theoretically, we thought the two would balance themselves but in reality, they put a lot of strain on the pulley and almost split the wooden support.

After several iterations, we finally came up with a design that was composed of three simple machines, not meeting all the basic requirements of the challenge. The final machine instead of having one human intervention point had two. The final design was composed of two inclined planes and a lever. The lever and inclined plane we put together using pieces of wood. We used a sock filled with sand as the weight in place of a stone because it was easier to adjust the weight. The mechanism employs four energy transfers:

  1. At one end of the machine, a rubber band holds the weight in place and a wedge holds the ball at another end.
  2. The rubber band is released and at that instant, the wedge is turned.
  3. The ball and weight move down the two planes with the ball arriving on the “launchpad” first. This is because the ball is lighter and moves on a shorter inclined plane.
  4. The weight, which is a sock loaded with sand is much heavier and on a longer plane so arrives later at the other end of the lever.
  5. The weight lands on one end of the lever and shoots the ball into the box.

Materials Used

  1. Plywood – for inclined planes and lever
  2. Sand – Weight
  3. Sock – Container for weight
  4. Rubber band – Trigger
  5. Nails and kebab sticks – for nailing components together.


This task has opened our minds to new ways of thinking about some of the local materials scattered around us. It has also shown us how some ideas may look very simple on paper but can be gruesomely difficult to build in the real world. It is indeed a perfect introductory work to a class in robotics as it has made us appreciate the importance of robots in our activities.




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