Oops looks like @hawkview beat me to it. I will leave it though. You can see several ideas.
I'm new to flying far away from myself, so I want the insurance if I lose control link that the rtb will engage and fly the plane toward me until I can regain control and take the plane over or I wouldn't mind if I had to flip a switch to engage the rtb.
This is very important and smart thinking. Two ranges to worry about. To fly close to max RC range, you must have RTB setup and all the pieces that means. To fly close to max FPV video range, you must use self leveling "Attitude" mode, else video goes out, you try to turn around and you don't know if you are upside down.
Important to realize that flying behind trees or really anything (hill, building, etc.) can make it loose connection.
The nano talon is a vtail, can I set up a mix for it to work with LP
Yes. Simple part of setup.
Is that RTB possibility? Can I set librepilot up to do what I just described?
Yes, but for fixed wing, it is a less documented, and more difficult procedure.
Is there anything else librepilot will need to engage return to base?
Mag/compass is required. This is built into the Revo class FC, but we usually recommend to use an aux mag built into the GPS you buy. DJI GPS is the easiest one to use as it puts both GPS and mag data on a single connection. Aux mag (vs. onboard mag) is a little less important on large aircraft or fixed wing than on quadcopter because fixed wing has only one motor and you can often install the FC farther away from mag field sources (ALL high current wiring with motor power on it). With aux mag, you can move it away from mag field sources (magnets and high current wires).
I have been looking at this gps. Will it work?
https://www.racedayquads.com/products/rdq-bn-880-flight-control-gps-module-dual-module-compass-with-cable
I believe that is a uBlox GPS and as such it will work.
I don't think it has a mag/compass if you want that though. It has a mag/compass that looks like it is compatible to work as an I2C (FlexiPort) (APM) aux mag. Ebay also has some cheap APM GPS/mag; about $16 shipped. Whatever you get, you will probably have to solder the correct connector on it.
I have been thinking of putting one of my quadcopter motors on it and that got me thinking about esc and what esc protocols are supported?one shot? BLheli_s? BLheli32?
Same ESC protocols are supported for fixed wing and for quads. Fixed wing does not need fast ESC response, so even 50Hz PWM ESC protocol is fine. Make sure your ESC protocol works with the version you want to use. You may consider using "next" instead of 16.09.
So if I put the revo nano in the plane and change the esc, I'm thinking I will need a bec, ubec, anything to provide power. So I think to keep things simple i think I should just run the flight controller at 5v so I can power servos off of it.
I fly 3 cell fixed wing with just the linear BEC built into the ESC and four 9g servos. I would NOT do that with more battery cells because of increased heat from linear BEC. Also, I always mount the ESC on the outside of the plane for good cooling. You need good cooling airflow for it to survive a whole flight.
I will be running 4 and 5 cell battery so I will need a Step down converter does anyone recommend one? Buck? Switching?
I have used the HobbyWIng 3A for some small purposes like that; functional and inexpensive, but I don't have a lot of aircraft that use them.
https://www.ebay.com/itm/HOBBYWING-RC-UBEC-5V-6V-3A-Max-5A-Lowest-RF-Noise-BEC-for-RC-Quadcopter-Drone/161905000720What voltage does Servos run at?
And how many amps do they pull?
I know they are all the different but would 1amp be enough to run 3 Servos? Or do I need 1 all per se
5V or 6V. 5V is fairly universal. 6V is for more strength and speed but really not needed for small to normal sized planes. Expect a couple hundred milliamps max per small servo when they are moving at full speed and not binding and much less when quiet. You can expect probably 500ma for all servos combined for a small plane and good servo linkages and hinges.
I have also been thinking a osd would be nice, does anyone recommend one or know where to get one?
MicroMinim OSD with MSP protocol is probably the standard here and elsewhere.
Failsafe is the key to RTB. There is RC based failsafe (RC sees signal loss and sends different servo pulses to FC) and FC based failsafe (RC stops sending servo pulses on signal loss and FC does all the failsafe stuff so modes and trims are set in FC). Understand and pick one and make sure it is set up and works (test it for a second with say full up elevator set up).
Onboard RF sources: Be aware that onboard transmitters such as FPV, telemetry and switching BECs can reduce your RC range and can also affect your GPS satellite count. I actually use OpLink as an LRS for several of my fixed wing GPS planes. Ground range test with these transmitters off and on to compare if they affect anything.
Twisting all high current wiring from battery to motor, and routing these away from mag sensor is important to help avoid these mag fields affecting mag sensor.
There are some extra things about fixed wing GPS flight. You need to enable GPS speed based PID reduction or your roll/pitch PIDs will oscillate (looks like flutter). I always leave rudder set to unstabilized manual. I always fly manual mode first. You need to adjust Rate, then Atti PIDs, finally Airspeed PIDs and several airspeed limits. Pick some flight modes to use with GPS. Test RTB "hover" LAST then longer RTBs. This is a long process to get it all working, but it is fun to make a waypoint flight and have it fly itself. You may need to set all waypoint error destinations to -1 to disable that if you don't have all your airspeed PIDs and limit settings done correctly. There are hacks to skip these setups...
Does your canopy have magnetic hold downs? That is a no-no. My testing show that the mag sensor needs to be over 1 foot / 300 mm from my mag hatch. I often mount my GPS/mag on top of the rudder to get it away from motor wires and hatch magnets.
One last thing. There is a PID windup in manual mode so that when you switch to Atti (Rate less so) it (aileron/elevator) goes crazy for a few seconds and you have to hold full control to make it more level. There are several work arounds. Reducing throttle
to zero when you switch modes zeros the PID windup (unless you disable that, don't disable). After setup, using Rate mode instead of manual stops the windup and feels very much like Manual. Also, I hear (from @jdl) that using a Stabilized#N switch setting, but setting all stabilizations for that switch position to Manual works around this (if I recall our conversation).
Personally, I think everyone should use a Bixler 1 for their first GPS plane.
You will definitely have a lot of questions.