This message is initially addressed towards Chris, since he has commented about this before, but I welcome any other feedback.Chris, you said that the ArduPilot requires 4 channels, which is why you are using an EasyGlider now. I think the reason is that the ArduPilot software processes two independent functions which are balanced against each other with appropriate weighting:1) Stabilization of the plane's attitude which uses the thermopiles to adjust the pitch and roll to within some nominal values.2) Navigation using GPS with velocity calculated heading and GPS calculated altitude to adjust position in X, Y, Z space using throttle (altitude) and rudder (heading).In reality, we know that stabilzation and navigation are coupled, as are the actuator channels of throttle, rudder, elevator, and aileron. However, in order to create an autopilot with limited resources, I assume that the two function were decoupled to get something working even it is not optimal. I do not mean even the slightest bit of disrespect by this, I am just trying to summarize what I think the design approach probably was. When and if I get more involved with this autopilot, I would like to investigate recoupling these channels to provide a more optimal solution.But in the meantime, I wonder why the RangeVideo OSD with autopilot says that it can command the EasyStar with only 3 channels? They seem to tying the performance of their autopilot function specifically to the EasyStar, which I presume is due its inherently stable flight characteristics that allow their autopilot to focus on navigation only. If this is the case, it seems to make sense that there could be a set of code developed for the Ardupilot that could be tailored to the EasyStar. I have pasted some of RangeVideo's FAQ text for their OSD below.Thoughts?Thanks!Pat********************************************************************************How does autopilot work?Safety options are automatically activated in-flight by the OSD if R/C signal loss occurs, and the feature is enabled. Works with both PPM and PCM receivers.The RVOSD has two safety options:1. Failsafe2. Return to home autopilotFailsafe goal is to bring airplane safely down to the ground.Return to home goal is to fly the airplane safely to the original takeoff spot.Failsafe is available on four channels.1. Throttle-failsafe2. Aileron-failsafe3. Elevator-failsafe4. Rudder-failsafeFailsafes are pre-set servo positions.Example: adjust throttle down and controls trimmed for a slow descent. The airplane will not return to the takeoff zone, it will just come down to the ground.Return to home works with three channels:1. throttle-autopilot2. aileron-autopilot or rudder-autopilot3. elevator-autopilotThe OSD sets the throttle-autopilot position to a cruise speed, and adjusts altitude with the elevator-autopilot, while steering with the ailerons or rudder-autopilot. This works very nice with airplanes like the Easy Star and SlowStick.The autopilot can only control either the aileron-autopilot or the rudder-autopilot. The channel, which is not used, is set to failsafe position. The failsafe position in autopilot mode is independent from the failsafe position in failsafe mode. For example, in failsafe mode you will want the airplane to descend in a slow turn. In autopilot mode, you need the airplane to fly straight, and have the other channel steer it home.
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Yes, your description of ArduPilot is correct. If you want a coupled autopilot, that's ArduPilot Pro.
As for the Range Video device, that's called a GPS-only autopilot, and to the extent it works, it only works on the most stable planes under the best conditions. It's is indeed possible to use ArduPilot as a rudder/GPS only autopilot on something like an EasyStar, but eventually you're going to crash. The RTLs like the OSD just offer this as a backup in case of catastrophe, so perhaps under those conditions you'd be willing to take the chance. But it's no way to make a real autopilot that works under suboptimal conditions.
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As for the Range Video device, that's called a GPS-only autopilot, and to the extent it works, it only works on the most stable planes under the best conditions. It's is indeed possible to use ArduPilot as a rudder/GPS only autopilot on something like an EasyStar, but eventually you're going to crash. The RTLs like the OSD just offer this as a backup in case of catastrophe, so perhaps under those conditions you'd be willing to take the chance. But it's no way to make a real autopilot that works under suboptimal conditions.