a couple of other pointers for you. you will only need 3 ni-cad packs saving 2kg. i would go with full pressure with a 70mm hydraulic ram cut down to suit robot with 3 burkerts in giving a really good flow rate. go for a good flow rate and you will have good flipper. and saving weight having 70mm instead of 100mm. the ram setup in my robot air was like this and it flipped a heavy robot and it hit the roaming robots roof. something i dont think has been done again.

of course you dont have to do anything i say its just my opinions.