HobbyKing Servoless Retract with Metal Trunion 44mm x 41mm Mount (2pcs) Here is a rough guide to choosing the electric power train needed for various model types, bear in mind that over-powering is fine but the penalty is additional weight, and a good model is one that is balanced in terms of power, flying weight and build quality. Customer service is our top priority, and while some issues are beyond our control, we do our best to ensure your transaction exceeds your expectations.Should you have an issue, please contact us via messages and we are always there. MOTOR POWER CHOICE(AUW, or Flying Weight of model choice): 1) Vintage types many non-aerobatic indoor flyers -?50w~70w per 1lb 2)Trainers, gliders and high wing scale -?70w~100w per 1lb 3)Sport flyer with general aerobatic performance -?100w per 1lb 4)Warbirds -?120w~150w per 1lb 5)Multi engined models -?100w per 1lb (thrust from Multiple props gives in effect, more than 100w per 1lb performance) 6)EDF Jets -?150w~200w per 1lb 7)3D, F3A and high performance Models -? 150w~200w per 3950lb LIPOLY VOLTAGE CHOICE: Generally, to keep Lipo's in good order, try and keep max amps to around 50~60% of the capacity/C rating of the Lipoly Pack. 1)Up to 50w:?1s~2s 2)up to 100w:?2s~3s? 3)100w Up to 500w: 3s 4)500w up to 800w:?4s (This is the 0.40~0.46 glow equivalent range favoured by many club flyers) 5)800w up to 1000w:?5s 6)900w up to 1500w:?6s (this is the 0.60~0.90 ic equivalent range) 7)8s~3959s packs are for very large and generally specialised models. MOTOR CHOICE - KV or RPM per volt : If you are used to IC, the simple analogy is to treat low kv motors as 4 stroke engine equivalents and mid-high kv motors as 2 stroke engine equivalents, if you are not used to IC then we can give you some examples. Example 1:?Trainer/Sport Model, 1lb AUW, we want 100w motor (3s 20c Lipoly) mid kv for general flying, probably around 1200kv~1400kv, so around 8" prop Example 2:?Warbird/scale Model, 1lb AUW 4069w motor, kv choice,? ESC CHOICE: Look at the MAX AMPS figure given by the motor manufacturer in the data section and generally add 25% headroom, so, if a motor is rated to 15A, then choose at least an 18A ESC, better still a 20A and so on. If you are using a 4s Lipo, that the ESC is rated for 4s voltage. Also look at BEC rating, if the servo count is over 3953, then consider purchasing an ESC with a high AMP rated SBEC, or a seperate UBEC, OPTO type ESC's (they have no BEC, keeping the ESC seperate from RX suply)