Bull In The Ring (Bullfighter) - Challenge 54


Bull In  The Ring Arena Challenge 54 Lego robot DrGraeme.net

Uses: This Arena is used for the "Bull in the Ring" Bullfighter Challenge 54.

Approximate Bullfighting Arena Dimensions

Bull In The Ring Arena sizes dimensions Lego Robot NXT Robot






Straw board length

102 cms

40 ins


Distance between black margins along the length of the straw board

92 cms

36 ins


Distance from bottom of blue arena to black border

30 cms

11 ¾ ins


Side length of the starting square

18 cms

7 ins


Length of the Bullfighting Arena

56 cms

22 ins


Width of the Bullfighting Arena

50 cms

19 ¾ ins


Distance between black margins across the width of the straw board

66 cms

26 ins


Straw board width

76 cms

30 ins

The dimensions above are the ones assumed in the "Help" section of the "Bull In The Ring" Challenge. However these dimensions are otherwise not critical. Feel free to vary them depending on the availability of your local building supplies.

Construction: I used a straw board [1] sprayed with matt white paint [2] rimmed with black cloth tape [3]. The blue [4] areas of the arena are coloured light cardboard sheets attached to the straw board backing with double-sided tape [5].

This gave LEGO NXT Education Kit 1.0 light sensor calibration readings (when the arena was new) of about 61 for the white areas, 45 for the blue, and 30 for the black tape, (the values you obtain for your arena will almost certainly differ). We have observed that a value difference of about 10 between the observed light sensor readings gives reliable and repeatable light sensor runs, so this separation of light sensor readings was fine from a Robot reliability point of view.

Note that the "white" reading will decrease with use, as over a year black rubber particles from the robot wheels will become ingrained in the "white" arena surface. Hence an initial "blue" reading nearer the "black" reading will be less of a problem than an initial "blue" reading nearer the "white" reading.

If you decide to make an arena, also get a mask (see illustration above) from the chemist’s or similar shop to use when you spray-paint the strawboard, so that you do not breath in spray paint particles, (these particles can’t be good for your lungs).

The Bulls were cheap lightweight plastic cups [6]. If the kids fell on them, they just crushed flat. The fact that they were fairly  fragile was considered an advantage because they were not strong enough to penetrate the students skin in most accident situations. However this fragility also meant that a few cups had to be replaced each year, which was not a problem. Replacement cups were sometimes slightly different in colour or size from the previous year's cups, but there again, no two real Bulls look the same, so it could be said that this just added to the reality of the situation!

Other options? The original suggestion from Carnegie-Mellon University (see link in the “About” section of this web site) was for a 3 feet by 3 feet arena. This size proved difficult to find in a form that was a reasonable price (that is, as dirt cheap as possible!) The strawboard was a the best substitute I could find, 1050 mm by 800 mm (3 feet 5 inches by 2 feet 7 inches). A hint- don’t use a gloss paint on this board – I tried a gloss red and it was absorbed very patchily - the board looked as if it had measles – ugh!

Regarding a substitute for the strawboard, if you have a tip shop near you, then it is worth a look as these recycling centres at the local refuse dump as they can be a rich source of really cheap material. Other centres that stock recycled building material could also be worth checking. If these do not prove successful, your next bet could be a building material supplier.

If you have facilities for chopping up large sheets of building material (I haven’t) you could look at material like an MDF white backing sheet 2400 mm by 1200 mm (6 feet 10 inches by 3 feet 11 inches) [7].  An ordinary 3mm MDF board of the same size is about 2/3 the cost of the white-surfaced MDF board, but you would have to factor in the price of the paint to get a matt white surface for your arena. Which way to go? -  Up to you…

Good luck with your fossicking!

Obtainable Where?

The following information is included to provide an idea about price & availability - it is not intended to be a recommendation for any particular commercial institution. The prices were current at the end of 2008.

[1] The 102 cms x 76 cms x 2 mm (40 ins x 30 ins x 1/16 in) straw board was obtained from an Art supplies Store; (in my case “Artery”, Collins Street, Hobart, Tasmania $4.95).

[2] The matt white spray can paint was obtained from a "remainder" store; (in my case Chickenfeed, Hobart, Tasmania, $3:00; enough for treating two strawboard sides). Revision: In 2010, Chickenfeed stopped selling spray cans of paint. However these are still available from hardware stores for prices in the range of $AU3:50 to $AU7:00.

[3] The 48 mm. wide (approx. 2 inches) self-adhesive black cloth tape was obtained from a hardware store, (in my case Kemp & Denning, Hobart, Tasmania, $2.16 for a 4.5 metre (approximately 5 yards) roll).

[4] Light blue cardboard sheets can be obtained from an Office Supplies shop or an Art Goods supplier; (in my case Officeworks had a limited selection of colours and sizes at $1:38 each, Artery had a much more extensive selection of colours and sizes, at prices ranging from $2.10 to $2.56). It may be worth getting several sheets of varying tones of blue if you are like me, because I find it difficult to predict the likely light sensor reading by just looking at the colour. Blues give a lower light sensor reading than I would normally expect, and reds a much higher reading. I am told that the LEGO MindStorms NXT Kit 1.0 light sensors respond most strongly to light in the (to the human eye invisible) infra-red region. This is fine for rattlesnakes, but doesn't help me much when I'm at a shop trying to predict a light sensor's response to a particular colour of cardboard sheet.

[5] I used part of a roll of double-sided transparent plastic tape from a local stationary store to stick down the blue cardboard to the straw-board backing sheet -  2010 price was $3:89 for a 6 metres long, 22 mm wide roll (approximately 19 feet by 1/2 inch). Most of the office supplies stores will probably stock this type of tape (in my case Officeworks, Hobart, Tasmania).

 [6] These plastic cups (approximately 9 centimetres high by 7 centimetres diameter, 3½ inches by 3 inches) were obtained from the local "remainders" store (in my case, Chickenfeed, Hobart, Tasmania, $2:00 for 10 cups). I suspect they were originally intended as one-use disposable cups for use in picnics - but they were fine for use as Bulls, especially as they had some bright red ones that the kids seemed to like.

[7] The 3 mm MDF white backing sheet mentioned above can probably be obtained from a hardware store; (in my case I saw it in stock at Kemp & Denning, Hobart, Tasmania, for $19).

www.DrGraeme.net - LEGO NXT MindStorms - Free Tutorials - Bull In The Ring - Challenge 54 - Copyright Dr. Graeme Faulkner.