RE: Electric Motor Primer
1. The battery manufacturer sets the 20C rating. 20 X .340A = 6.8A
2. C is the Capacity of the pack. A pack that can be discharged at 20C can be discharged at 20X it's capacity. The discharge rate has no bearing on the charge rate..all lipos must be charged at no higher than 1C. So the 340Mah can be discharged at 6.8A (20C), but must be recharged at 340 milliamps.
3. No, the motor will only draw as much as the load (prop) and voltage determine it will. Having a pack rated for more than the motor can draw is good, having a motor draw more than a pack can deliver is bad, and will ruin the pack. You would burn the Axi up if you put too much load (too big of a prop) and tried to run it at 10A, but the 10A capable battery would be fine.
3A. You can order direct, or PaulSwany in the ProBro section is a dealer.
4. The 2015-5400 has a Kv rating of 5400 RPM per volt. This gives a good speed at 7.4V (2S lipo). 39960 RPM (theoretically..) divided by the popular 6.6:1 gearbox gives about 6000 RPM. Of course the prop won't turn all of that, maybe 4500. Take the 2015-2800 and it has (I'm guessing..) a 2800 Kv or 2800 RPM per volt. at 7.4V, this is only 20720 RPM. Now you could run say 4:1 ratio and get a theoretical prop RPM of 5180, or you could run 11.1V and get more RPM, but you now have a 3S battery to tote. Generally speaking, the higher Kv motors are happier on low voltage and low Kv motors on higher voltage so things even out. There are exceptions, I'm just talking about general 3D type flying.
5. The Axi is an outrunner, a special kind of motor where the outside of the motor turns and the Himax is an in-runner, the shaft turns but the can is stationary. The Axi has a Kv of about 1020 seems like, so at 7.4V it only turns 7500 or so RPM...pretty close to what you want to turn your prop, so no need to mount it in a gearbox. Of course the RPM will come down when the prop is mounted, and the amps will go up. And the outrunners, being mounted 1:1 with the prop, are not as flexible as a geared motor....go up just a little too much in size and the amps can come WAY up, you don't have the reduction of the gearbox to help minimize the effect of overpropping. Now it's just a matter of selecting a prop that flys the plane like you want, and does not make the motor draw more amps than it or the battery can handle.