i have a few questions about my new APM2, going on to my Y6-Copter so i thought, I'd bundle them here:
1) How come, if i have the Power-Jumper deconnected, and the BEC going into the APMs Input rail, I don't get my reciever to power up, even though it is connected with a Female-Female Cable going to the Input Rail?
2) In the APM2 manual ( http://code.google.com/p/ardupilot-mega/wiki/APM2RCSetup under point 2) ) when talking about the flightmodes, it says mode 6 always has to stay manual, as a Hardware-failsafe-backup. Does that still apply to the newest APM2? Because if i go into the flightmodes menu, i can't even find "Manual" to choose from the list, and it was by default on "stabilize" in mode 6
I'd be happy about any answers!
I'm going to be honest, and looking at total EMI, RFI rejection, I personally believe in always powering the APM from the output pins and in your case, one of the dual BEC setups intended for dual battery emergency systems is more in line. This way, the theory is that the system runs as normal off the main battery via the dual BEC. Should the unthinkable happen, the smaller battery powers the radio, APM and servos to land.
Your original plan is not bad, you likely already have the components and it should work fine.
Personally, I would separate the power pins off the servos isolating them to the ESC BEC, power the APM with the other BEC, but in order to do that effectively, you need more wires and jumpers and so yet another set of failure points. Thus,l even my plan isn't perfect.
It goes back to my older hobby of 60 size nitro RC helis. We used NiCads and NiMH to run the radios and servos for years and then Lipos came out, but needed regulators. Quickly the community found out linear regulators will overheat and shutdown with high servo loads thus a crash. Soon came out switching BECs, but then they caused RFI casing crashes. So then there were dual BECs, dual batteries and a whole host of wiring and power distros (powering servos from 6 volts while the rest of the system is at 5 volts) but all the connectors and wires led to more crashes. Bottom line is that we could discuss this all day and add lots of expensive hardware, but all you want to do is fly.
Also, your original concern of the BEC dropping to 4.8 volts is trivial in the normal RC world. Most systems are designed for 4 each 1.2 volt NiCds so 4.8 volts was the best you could hope for. Additionally, the APM Arduinos will run all day at 4.5 volts, and even maybe around 3.5 at stock clock speeds since all they do is lower the clock on the 3.3 volt versions of arduinos. The sensors are further on a 3.3 volt regulated bus, so they might not ever even see any of this. Obviously we want clean power and that's what both of us are trying to do, but at some point, all of this may be overkill and a simple capacitor would have solved the short term high current draw demands of the servos. Also, heavier wire from the original ESC BEC could be the entire solution to the voltage drop under load. I highly doubt the regulator sags that much, it's all in the wiring.
Hi Vernon, thanks for your detailed explanation. It really helped to understand things better. Final decision has been made to buy a better ESC with integrated 5A switching BEC which should deliver stable 5V to the APM through the output rail (or at least much better than the 2A linear one from the other ESC). Again thank you.
Be sure to let us know how it works. The one thing about the forum is that we hear problems all day long, but a good success story is nice.
Thanks Vernon, i'll receive the ESC next week and keep you posted with the results.
Iam very new to this and i would like to say what a great piece of kit the APM2 is.
I have successfully flown an Easyglider on many missions straight out of the box (i did do the twin-ailerons mod though).
Iam now putting the APM2 in my Cularis.
I was worried about the Cularis ESC/SBEC putting out 5.5v to the APM2 so i searched for advice and found this thread - and iam very glad i did.
My plan was also to run a separate SBEC of 5v from the same battery powering the servos.
Anyway, my point is that I think it should be made clear in the instructions as a 'Warning' not to use the same battery, to avoid anyone putting their APM2/Aircraft at risk.
Or maybe iam just stupid.
My solution in the end was to purchase an ESC/SBEC that puts out 5v.