Mentor Notes.

Challenge 22 – Around the Moon


Students teach their Robots to proceed in a curved path.


Students have already achieved he task of making their Robots go a known amount forwards and backwards in a straight line. The purpose of this Challenge is to add to their skills the concept and practice of teaching their Robot how to proceed in a gentle curve.

The Challenge:

The Challenge is to leave the "Earth" (the blue circle on the right below), circle the "Moon" (the nice heavy bottle of my favourite lime cordial on the left below – but feel free to choose your own flavour!) Instead of being "lost in space", the Robot should then end up back on "Earth" (inside the blue circle).

Around The Moon Arena 

A video of this can be seen by clicking here (broadband) or by clicking here (dialup).

Constructing an Arena.

Theoretically, it is not necessary to use a pre-constructed arena; a couple of marks on the floor would suffice. However if the "Earth" and the "Moon" move when they are hit by errant Robots, this can cause the following students much frustration because the Earth-to-Moon distance will almost certainly change, and their carefully crafted programs will not work the second time they run them! After experimentation at several schools, I found an arena just about necessary in practice!

My arena was constructed from a sheet of black cardboard (I used black because astronauts comment that space appears black) measuring 84 cms. by 15 cms (approx. 33 inches by 6 inches). The blue circle shown on the right side of the diagram below was cut from blue cardboard by tracing round a CD (approx. 12 cms or 4 ¾ inches diameter) – blue because the Earth is called "the Blue planet" because of the amount of its surface covered by water. The "Moon" was cut from green/yellow cardboard by tracing around a jam-jar lid (approximately 765 mm or 3 inches diameter) – green because the moon is made from green cheese(???) The bottle is a full 750 ml. glass bottle of (lime) cordial. I used glass because it is heavy (less likely to move when bashed by errant Robots) and the classrooms had carpeted floors with little chance of the bottle breaking. If you are working on a concrete floor, a plastic bottle would be less risky. The distance between the nearest points of the blue and green/yellow circles is approx. 61 cms. or 2 feet.


I used these dimensions because several arenas can fit nicely into the classrooms in which I assist, and they do not cause problems transporting them from School to School. Apart from these constraints, none of these dimensions is really critical, as long as they do not change during the Challenge.

Source of Materials

The cardboard sheet can be obtained from an Office Supplies shop or an Art Goods supplier; (in my case local store "Officeworks" had a limited selection of colours and sizes at $1:38 each, and "Artery" had a much more extensive selection of colours and sizes, at prices ranging from $2.10 to $2.56). These prices were current at the end of 2008. 

The Far Side of the Moon - Tutorial  - NXT-G - LEGO MindStorms NXT -