What is the point in using a 7.4V Li-Po if it is essentially the same as a 9.6V? Is it smaller in size or something?
No, they are not the same, and anyone who tells you they are the same is ignorant to boot.
A 7.4v LiPo charges to a MAX voltage of 4.25 volts per cell (8.5 volts for a 7.4v, although most chargers cut off at 4.20 volts per cell, so 8.4v's) A fully charged 9.6v should be damn near 12 volts fully charged and should hover around 10-10.5 volts for the life of the pack while in use untill the end of the charge.
Assuming you have a battery that can supply the sufficient amperage for hte motor to operate at max without maxing the pack... the 9.6v will ALWAYS provide a higher ROF and better trigger response than a 7.4v LiPo could ever hope to produce.
Lets start by examining some very common figures: Amperage, Voltage and Capacity ratings for some quality batteries:
7.4v 3000 mAh 15c (45 amp continuous discharge)
9.6v 4000 mAh 10c (nominal, 40 amp continuous)
Power for Electrical circuits = Voltage * Current and comes out with units of watts:
7.4v * 45 amp = 333 Watts
9.6v * 40 amp = 384 Watts
Thats assuming nearly depleted for a NiMH pack and at nominal voltage for a LiPo, lets compare operating voltages and max current draw of 35 amps (Very very very power hungry setup, most AEG's are around 15-20 amps) You have to keep in mind that a motor will only take the amperage it needs to provide max torque and wont draw more than it needs.
8.0v * 35 amps = 280 watts
10.25v * 35 amps = 358.75 watts
What does it mean? Well, technically ROF is controlled by free running RPM and Torque. Free Running RPM is almost purely voltage dependent, where as Torque is dependent on a mix of Voltage (as torque requires movement and thus RPM) and amperage. ROF is a result of both RPM and Torque and therefore mostly voltage and torque. Assuming your motor is capable of supplying enough torque to run at max RPMs (unrealistic, truely) for the motor then voltage is very important. Higher voltage will provide a better trigger response. Ergo: The 9.6v pack will always produce better ROF and consequently Torque.
Why a LiPo then? Well a 7.4v is usefull for guns with incredibly small battery spaces and still want a decent ROF. Because ROF requires that a pack have amperage, most NiMH and NiCD's in the sizes that would fit wont provide the amperage necessary to provide the most Torque so ROF suffers. In larger guns or guns using external battery packs, the 9.6v will always provide better trigger response and ROF.
We've just talked about 7.4v's, now what about 11.1v's? An 11.1v should charge to aprox 12.75 volts (realistically about 12.5-12.6 volts) and operates around the 11.75-12v range. This would be a more realistic comparison to a 9.6v. Although to be fair an 11.1v is closer to a 10.8v in terms of ROF.
Dont believe me? Do the tests yourself (or wait for me to charge my 7.4v 3000 mAh 15c LiPo
) I can guarentee that the 9.6v will ALWAYS produce a better trigger response and ROF than any 7.4v you throw at it.
