Copyright © 2009-2010 Eagle Tree Systems, LLC
http://www.eagletreesystems.com
Page 13
Safety Mode Overview
Please read this entire section, and understand the function and limitations of the modes, before enabling a safety mode!
IMPORTANT SAFETY MODE INFORMATION:
•
RTH is an advanced feature requiring pilot tuning and calibration, and is used only at your own risk.
•
WARNING: Since RTH may increase the throttle setting, YOUR MOTOR MAY START SUDDENLY WITH YOUR MODEL ON THE
BENCH, OR ON THE GROUND, WHEN RTH IS TRIGGERED! RTH attempts to avoid starting the motor in this situation, by
examining the speed and altitude of the model. But, if the GPS or other sensors are misreporting altitude and/or misreporting speed, RTH
could still start the motor on the ground. ALWAYS ASSUME THAT THE MOTOR MAY START AT ANY TIME, WHEN RTH MODE
IS ENABLED!
•
When RTH activates, if the GPS fix quality is not good, RTH will program your throttle to the setting you entered for “Motor Off” during
the Safety Mode Wizard.
•
It is strongly recommended that you set the “Capture Rate” of your eLogger or Recorder to 10 samples/second, since this setting controls
the rate at which the OSD Pro receives information from the eLogger/Recorder. The more information received by the RTH feature, the
better.
•
RTH is a safety feature of last resort, should you lose radio contact with your model. Never rely on the RTH function to fly or navigate
your model. Never fly out of the manufacturer’s recommended range, or fly outside VLOS (Visual Line of Sight).
•
When enabled, Safety Mode will activate based on the How the OSD Pro Determines when Safety Mode should be Invoked section below.
Read this section carefully!
•
RTH will work best with very stable, self correcting airplanes, and will not work reliably with flying wings, aerobatic planes, helicopters,
or similar.
•
We recommend using rudder for RTH, if your plane is equipped with both ailerons and a rudder. This is because there is less banking
with rudder turns than with aileron turns.
•
RTH performance can vary depending on the flying conditions, the type of airframe, the degree to which it has been configured for your
model, the GPS fix quality, and potentially other factors.
•
Never intentionally turn off your radio to test RTH in the air. There is a chance that your receiver will not link back up with your radio,
especially with 2.4GHz radios, which could result in a crash. Always use the “Test RTH” menu item to test RTH in the air.
•
RTH will NOT engage if the GPS signal quality parameters are below the minimum quality you specify in the “GPS and Waypoint
Settings” menu. Failsafe Safety mode will engage instead.
•
RTH will NOT fully engage if your altitude is less than 60 feet/20 meters above ground level, or if your speed is less than 3 MPH or 3K/H.
•
If you routinely fly near to the maximum range of your receiver, and have periodic link dropouts from which you are able to recover after
sluggish model performance, Safety Mode may engage when you don’t want it to. Safety mode is not intended to be used if you routinely
fly beyond the maximum range of your receiver.
•
It is strongly recommended that RTH mode not be used by inexperienced pilots, until they are comfortable with all aspects of flying.
There are two safety modes:
Failsafe Mode
In Failsafe Mode, the OSD Pro returns the servos to a pre-determined failsafe position if radio contact is lost. If your Receiver supports multiple
programmable failsafes, the Failsafe Mode safety is not particularly useful. If you have a receiver that does not have failsafe capability, and does not hold
the servos at the last position (your servos move randomly if radio signal is lost), or a radio with only 1 programmable failsafe, then the Failsafe safety mode
can be used to set a failsafe on all three of your control surfaces, in the event of radio signal loss. The failsafe servo positions are chosen during the Safety
Mode Wizard, described earlier in this document. The “Level Flight” aileron/rudder and elevator settings you indicated, and the “Motor Off” throttle
setting you indicated during the wizard are recorded for use as the Failsafe Mode failsafe settings.
Return to Home Mode
Return to Home (RTH) attempts to recover your model if you lose radio contact. Both traditional fixed wing models, and elevon or vtail models, such as
flying wings, are supported.
The RTH uses enhanced implementations of Proportional, Integral, Derivative (PID) controllers to adjust the model’s altitude and direction. Specifically, a
PID controller is used for turning, and a PD controller is used for climbing. More information on PID controllers is available here:
http://en.wikipedia.org/wiki/PID_controller
.
The PID controllers use GPS course, speed, altitude and other information to attempt to return the model to home. NOTE: a later version of the firmware
(downloadable from our website) will support an enhanced RTH algorithm which also uses attitude sensing to enhance the RTH feature. Also, note that the
use of the FMA
TM
Co-pilot
TM
can improve the operation of RTH. See the section above on configuration of this optional equipment.
Additionally, RTH manipulates the throttle to control altitude and cruise speed.
How the OSD Pro Determines when Safety Mode should be Invoked
The OSD Pro constantly monitors your receiver to determine if the selected Safety Mode should be invoked. The things that trigger Safety Mode vary
between receiver types.
For receivers which do not hold the servos at the last position or failsafe position when signal is lost (the servos either go limp or move randomly when the
Transmitter is turned off), the OSD Pro looks for bad pulses (pulses of the wrong duration), or the absence of pulses. If enough bad or missing pulses are
evident in a short period, Safety Mode is invoked, until the error rate decreases to a good level.
