I've read lost about FBW on the wiki, notably this article (https://code.google.com/p/ardupilot-mega/wiki/FlightModesFlyByWire), which describes the mode as attitude control with manual throttle.
I'm using APM 2.4 and my FBW A runs my prop at 45% or so. There are several places in the documentation where this is contradicted.
What's going on here? Is that prop supposed to spin or not? I'd prefer it not to, honestly. 45% is a big waste of battery when you're already at altitude and you had some gliding in mind.
Is anyone else seeing this?
This is a known problem.
Unfortunately the administration controls the WIKI, so it can't be changed until someone in power here decides to do it.
Only one user so far has been injured by this faulty behavior, so it's not yet a priority to correct this in the manual or code.
I noticed that... I remember reading that someone had their plane take off from the bench during FBW_A. Mine did too, but I was up at the nose so the prop hadn't had a chance to get me before I pulled the plug.
I wonder why throttle is enabled in A? Seems odd that the intent was very clearly to have A & B differ in this way. Does anyone know what version of code this changed in?
Is stabilize supposed to control throttle, too?
No. The only times the APM should be controlling the throttle is in FBW-B mode with the airspeed sensor and in auto modes.
It makes sense to put the airspeed sensor to work in FBW-B to control the throttle. And obviously in the auto modes the autopilot must make a choice about throttle.
Oddly enough, comments in the code itself describe fbw_a as 'manual throttle.' This seems beyond a wiki issue.I opened issue 693 for it.
Here's the link: https://code.google.com/p/ardupilot-mega/issues/detail?id=693
In FBW-A, check your THR_Min, as for example if yours is set to say 30%, the min throttle will be 30%...
above that setting you have full control, but it applies the minimum.
Found out the hard way when an 18" prop thwacked my knuckles.
Most smaller airframes, we need a min of 15-20% to keep the decsent rate to an acceptable level (so we set it to that or there abouts), so when the AP pulls right back, this is the minimum, and is def applied to FBW-A
i would, if i were you. set it 5% (be aware it will start on its own) and test from there, this way at least you will be familiar with its behaviours. (or set it to 0% Min, and it will do nothing, but this may not be the best setting if considering going into Auto)
FYI STAB mode you have full control over throttle (as in it starts at the bottom)
either way this deosnt matter as long as you know what to expect.
Anyway, FWB_A & B are testing modes primarily, if you look at FBW_A from that perspective, haveing a low cruise throttle makes a fair amount of sence, as you still have full control over flying speeds etc.
Hope this helps
As you said, min throttle is probably the culprit here. It exists for gas planes that need a minimum throttle or the engine will die.
FBW-A is not "primarily" a testing mode, and if FBW-B is a testing mode at all then it is a really useless one. I take off, fly manually and land primarily in FBW-A. It is by far the best mode for doing so.
The idea that 15-20% throttle is NOT necessary on any common DIY UAV platform. Most of them have perfectly good glide ratios. Min throttle is for gas engines and it is probably a bad idea to set it unless you have one.
Min throttle has no use for gas engines. That's what your idle set speed screw is for. Gas engines don't just die when you let off the throttle if they're setup right and running properly.
I have to agree with Jake here.....
IC engines as he says are, if set up properly wont die, but what you do need it a kill switch of sorts (apart from being a legal requirement) you dont want it buggering off into the bright blue yonder if summet goes horribly wrong.
Which is what happens, if your TX is set up in manual to do exacly that.
However, over the last 6 years with all the AP's from here, FWB is the mode i use to test and set up with, and on the very odd occasion, use for training a complete beginner, and or a bit of FPV, to make it much easier when managing longranges and high data flow, but lets face it, if you buy an AUTOpilot...you want it to do AUTOpilot stuff, otherwise you would buy a cheap £40 stabilization system, the size of a postage stamp.
Now that i know what FBW_A does, i like it....it gives us more options, in a real world(not bench) situation.
I should mention a recent breakthrough on this issue--I reloaded the firmware to the board once again, with the same param file and FBW_A and Stabilize worked as described. Not sure how that works... but it did. I had the new incarnation of the plane in the air yesterday and it does what it should now. Jack, try pushing the firmware to the board again... worked for me somehow.
I would like to reiterate proper model safety, When working with the electronics of any R/C aircraft, Ensure that all the propellers and blades are removed. I learned that the hard way when a 250 Helicopter flew across my living room during radio setup. I thought I disconnected 2 esc connections and apparently did not.... This was on a regular dumb R/C with no autopilot.