I have a scratchbuilt project (FW-190) whose mechanical retracts would make me much happier if I could drive them with linear motion - - push/pull. An air conversion would do that. But I don't want to spend any more weight and install any more equipment than necesary to get that done. So...how small (aka 'light') an air tank and air cylinders can I get away with if I will tolerate two up/down cycles between charges? Any benefit to parallel use of two small tanks?

Alternately, could I use a pair of S-148 servos converted to linear motion, one servo per gear leg (retracts are .40-size Thunder Tiger with 3.5" Dave Brown foamie wheels) to drive the retracts, assuming that the linear travel is long enough?