Specifications

motor pinion is 18 tooth, then the gear ratio will be 180:18 or 10:1.
The final headspeed will be the motor RPM multiplied by this gear ratio, multiplied by about
0.85 to simulate the loading effect of the main rotor blades.
So: 2006 (motor Kv) * 9.6 (battery voltage) * 0.85 = 16369 RPM motor speed
16369 * 18 (motor pinion) / 180 (main gear teeth) = 1636.9 RPM head speed
For a fixed pitch helicopter, you should plan to have double the hovering headspeed at full
throttle so the helicopter will hover at approximately half stick.
Note
The 0.85 multiplier is the speed drop under load, which is a rough estimate. It is
NOT an efficiency factor. If a motor is inefficient, it will usually consume more cur-
rent rather than dropping RPM.
30.11.2. Estimating power consumption
R/C helicopters need about:
• 100 watts/kg for hovering
• 150 watts/kg for entering/exiting forward flight
• 200 watts/kg for light aerobatics (loops/rolls)
• 300+ watts/kg for serious 3D flight
(add up to 50% for higher headspeeds)
Since watts = voltage * current, we can divide the watts by voltage to estimate the amps re-
quired. For example, an ECO 8 weighs about 1.5 kg. From this, we can estimate the power at
hover:
100 watts/kg * 1.5 kg = 150 watts
For a 10 cell nicad pack, this would be:
150 watts / 12 volts = about 12.5 amps
Note that the 100 watts/kg value is an average power draw during hovering. It is not safe to
hover a heli with a 100 watt/kg power system, because extra power will be required to recover
the heli safely if a gust of wind blows, etc. A realistic minimum power system would be about
150-200 watts/kg.
Power consumption is very dependent on motor and headspeed. For example:
• ECO 8 w/Mega 16/25/3 at 1400 rpm HS: 105 watts/kg to hover
• ECO 8 w/Mega 22/20/3 at 1600 rpm HS: 174 watts/kg to hover
Technical Appendix
213