Gearbox ratio selection help
Working from Motocalc i have come up with 2 motor/gearbox sets for my 69" BT spitfire driving a near scale 16.2" prop.
Scorpion S2-5525-210KV at 1.25:1 and a Scorpion HK5020-450KV at 3:1.
Is there a prefered ratio region?
I've got a $$$$ Hacker A50-16S motor that turns a 16X12 APC-E prop direct drive from a 6S2P A123 battery pack. That A123 battery pack would be close to a 5S 4000 Mah LiPo. Perhaps other less costly motors can also do the job? This A50-16S motor turns my 16X12 prop at about 6000 RPM while pulling about 55 Amps, and 1000 Watts.
Hacker has a number of different motor "winds" on the same size motor frame for use with different number of cells in your battery pack.
When using a gear drive:
There is a slight advantage to a ratio that is not x.000:1 Best will have x.xxx:1 where no (x) number is 0. This ensures that each tooth must hit many other teeth before hitting the same one again so that any small defect will take longer to progress into a broken tooth.
Not a huge consideration for us.
Direct drive is better, mechanically... when you can do it.
Geared is better for efficiency if the gears are of high quality. A low kV motor wastes more energy than a high kV motor because electric motors simply work better at higher rpm. The efficiency differences for our purposes is again very small because small motors tend to be a bit inefficient anyway.
So in the end: Pick the setup that makes the prop turn the rpm you need. It will be fine.
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