Nice pretty blue Gearbox

Man, I don't know beans about this stuff compared to those guys. About all I do is try to concentrate on finding stuff that works for other guys and use that.

And that's pretty much where the 4100~4200Kv motors on 3S lipos and 6.6:1 gearing comes from. It's just kinda been settled on as pretty much optimal for 3D on foamys.

The 4100Kv means that for ever volt you put into the motor, it'll turn 4100 RPM with no load. So your 11.1V lipo will turn it about 45.5K. Now when you gear it down 6.6:1, it should turn the prop at about 6.9K. In reality, the battery voltage will drop some under load, and it bogs the motor down some turning the prop, so you don't really get 6.9K on the prop.

Seems like the Himax 2015 4100 spins a 12X6 GWS at about 4200 RPM.

It takes a certain amount of power to turn a given prop. So you might think you could just slap a higher ratio on the gearbox and spin the prop faster. You could spin a prop faster, just not the same prop. The motor and battery will only combine to produce a fixed maximum amount of power, and turning the same prop faster means more power. So you have to go to a prop with less load, like smaller diameter or less pitch.

For 3D, you probably want the biggest prop, so the lowest ratio would be needed. It sure wouldn't hurt to try the next highest ratio and say a 10X4.7 prop. It'll spin faster so you might get similar thrust.

Which brings us to the higher Kv motors, like the 2015 5400. If you run the calculation on voltage, you will see that in theory the 5400 would spin a heck of a lot faster than the 4100. So why not use it?? Since it takes more power to spin the same prop faster, the 5400 would have to make more power than the 4100...but they are both rated at basically the same power level. So you have to run a smaller prop and turn it faster. You could gear it down, but 6.6:1 is the lowest ratio you have.

Or run a 2S lipo. Doing the voltage calculations now at 7.4V, it turns fairly close to what the 4100 did at 11.1V. And there are some gearboxes out that would allow you to gear it lower than the 6.6:1 GWS D ratio.

So Himax sent 3 sets of gears with the gearbox. The lowest one is "3D Ratio with a 4100 and 3S" the others might work on a warbird and the same motor, or for a different Kv motor, or a 4100 on 2S so you spin the prop faster.

So what I get from this.... in general;
the higher the gear ratio, in this case the 6.6 I would get higher torque at low speeds, and lose flat out speed at the top end. Which is fine for the foamies, as I'm really not looking for flat out speed.

the lower the gear ratio, like the 4.3 would be used for planes with higher wing loading, and needs speed to keep flying, but as a general rule, don't bother trying 3D stuff, as it may not have the torque.

I realise that other things come into play, such as proper selection of motors, props, number of cells in a battery, current cpacity, et all. I just wanted to focus on gear ratios at this time.

Yah, I could spend time at all the other places, but I'm having trouble making time for the Attitude I'm trying to build, in time for my Winter Electric Fly-in, which is a few months away. The next project is going to be the ChuckieFlyer. I'm a member of several of these forums. When I go there, sometimes I'm surprised that my name comes up as an already joined member. too many of them, and not enough time.