XCell Spectra-G Model – Additional Operators Guide
Page 8 of 16
Copyright
12/5/2004
Miniature Aircraft USA
3.6. Throttle Setup
Make sure the idle position screw has been backed out such that the throttle butterfly can
close completely without touching the idle screw. Also make sure the return spring has been
unhooked from the carburetor body. Its tension will put undue force on the servo which is
unnecessary.
As per the kit instructions, the carburetor throttle arm should have been installed so that it will
be exactly at 90 degrees to the engine at ½ throttle. This is at the optimum position for best
throttle control.
Install the servo ball link at 13mm from the center of the servo. This will allow full deflection of
the servo and throttle at 100% travel in each direction which will allow the best control
resolution of the throttle.
A good initial throttle curve is as follows (this assumes 0% is throttle closed fully)
Five Point Curve
1
10%
2
25%
3
50%
4
75%
5
100%
If your radio supports more than 5 points, match the low, middle and high points and then
interpolate all points in between.
This is just a starting point, you will need to adjust this curve for your particular combination of
rotor blades and pitch curves to match your RPM requirements.
3.7. Throttle Governors
Throttle governors work very will with the recommended throttle setup. Although there are
several on the market, extensive testing has been done with the Futaba GV-1.
Use a throttle servo recommended by the governors manufacturer for compatibility, although
faster is better.
Regardless of manufacturer, all of the governors require a magnet and pickup be mounted,
usually in the fan. On a gas model, this is particularly difficult to complete because there are
not standard mount points for the sensor. MA recommends the use of the Stator Gator optical
pickup for use with the GV-1. This device can simply be plugged into the “black” wire from the
engine ignition system on the G231 and G26. It has proven to work very well and is simple to
install. The wires on the stator gator are long enough that the unit can be mounted easily;
however make sure they are secured to prevent them from being eaten by the drive train.
The Stator Gator control location is not critical as it will not cause any radio interference.
Follow the governor manufacturer’s instructions for setup of the unit itself. Make sure you use
the correct gear ratio. The stock gear ratio is 7.15:1.
