▁detect ▁the ▁inf ra red - em itting ▁ball ▁and ▁use ▁this ▁as ▁well ▁as ▁other ▁special ised ▁sens ors , ▁such ▁as ▁son ars , ▁comp ass es ▁and ▁cam eras ▁to ▁locate ▁themselves ▁and ▁the ▁opposition ' s ▁goal . ▁ ▁These ▁rob ots ▁must ▁each ▁be ▁able ▁to ▁fit ▁into ▁a ▁cyl inder ▁which ▁is ▁ 2 2 0   mm ▁in ▁diameter ▁and ▁height . ▁ ▁Origin ally , ▁the ▁s occer ▁field ▁had ▁a ▁gray scale ▁pl astic ▁floor ▁allowing ▁the ▁rob ots ▁to ▁locate ▁themselves ▁along ▁the ▁field . ▁ ▁In ▁ 2 0 0 7 , ▁this ▁was ▁replaced ▁with ▁the ▁G EN II ▁( Gener ation ▁ 2 ) ▁field ▁which ▁had ▁different ▁sh ades ▁of ▁green ▁pl astic , ▁which ▁allowed ▁light ▁sens ors ▁to ▁be ▁used ▁to ▁more ▁accur ately ▁determine ▁location ▁( this ▁field ▁is ▁still ▁used ▁in ▁Australia ▁and ▁is ▁now ▁also ▁used ▁in ▁the ▁World ▁Rob ot ▁Olymp i ad ). ▁ ▁In ▁ 2 0 0 9 , ▁the ▁field ▁was ▁replaced ▁with ▁plain ▁green ▁felt . ▁ ▁This ▁change ▁was ▁aim ed ▁at ▁making ▁the ▁game ▁more ▁real istic ▁by ▁creating ▁greater ▁reli ance ▁on ▁the ▁goal ▁location ▁and ▁walls ▁rather ▁than ▁the ▁ground . ▁ ▁The ▁change , ▁however , ▁has ▁been ▁controvers ial ▁with ▁many ▁teams ▁having ▁problems ▁with ▁quality ▁of ▁the ▁felt . ▁ ▁When ▁Rob o C up ▁Junior ▁was ▁first ▁formed , ▁almost ▁all ▁teams ▁used ▁L ego ▁Mind st orm s ▁construction