Make sure your ESC brake is programmed to Off.
"Brake" refers to what happens when you reduce the throttle level to zero. If the brake is "off," when you reduce the throttle to zero, the prop will freewheel. That is, the prop will spin due to the plane moving through the air. For most types of flying, you want the brake "off."
If the brake is "on," the ESC will stop the prop from spinning when the throttle goes to zero. The most common use for the "on" setting is when you are using a folding prop. A folding prop won't fold if the prop is free to turn.
With most ESCs, the brake can be set to either "on" or "off" by programming the ESC. Instructions for programming should be supplied with the ESC.
Also, be sure to use an ESC with the proper 9V cutoff when using 3-cell Li-Po packs, or 6V cutoff when using 2-cell Li-Po packs.
With lipo batteries, it is important that the batteries never be discharged below 3 volts per cell -- 6V for a 2-cell lipo and 9V for a 3-cell lipo. Discharging a lipo below 3V per cell can permanently damage the battery.
Most ESCs have a feature called Low-Voltage Cutoff or LVC. When you are flying, the battery voltage will be continually decreasing as the battery is discharged. When the battery voltage decreases to the LVC value, the ESC will cut off or reduce power to the motor while continuing to deliver power to the receiver and servos. In this way, the ESC protects the battery from being over-discharged while still allowing you to control the plane and hopefully make a safe landing.
With many ESCs, the LVC point is programmable. If you are using a 2-cell lipo, you set the LVC to 6V. If you are using a 3-cell lipo, you set the LVC to 9V. Some ESCs automatically detect the number of cells you are using and set the LVC accordingly. ESCs vary widely in the way the LVC is set, so consult your ESC's instructions.
- Jeff