I have just bought the ArduPilot Mega 2560 Full Kit... plus the Triple Axis Magnetometer HMC5883L. I should have it built over the weekend.. then i'm off to a my mates machine shop, and i'll make the splitter plate for the lower frame onto which i am going to fit the Ardupilot. the magnetometer i'll put on the tail as suggested. I am going to use my X-cell Razor 600E. For those that dont know its around the 50 size nitro heli.
Do i need to buy any other sensors i.e. the Sonar... i can fly a helicopter all day long but this is my first time flying one with stabilisation so any tips would be gratefully appreciated.
If this works well then i am going to try and use it on my x-cell gasser. i can get up to 20 minute flights with this. But i think for the time being a battery 600 is the way to go.
i'll post some pictures when i have it all together.
No, the tails don't wag when they're hovering. It just stays where they left it in the heli frame of reference.
If the gain is marginally high then the tail may not wag in a steady hover but it can when the heli moves quickly along the x-axis due to translational lift in the tail rotor.
They do use the fastest servos they can get for the tail and change them out when the tail starts to get a little sloppy.
A typical setup procedure would be to find the gain that just under the threshold that produces detectable wagging when going fast and then back off 10 .. 20% or so. If the gain is set too high the tail servos have unacceptably short life times.
The high end tail servos have a center pulse width of ~750 us instead of the normal 1500 us. This is so the PWM update rate can be increased. PWM input of 500 us .. 1000 us means the update rate can be 800 Hz.
Using normal 1500 us center digital servos you could go to the 400 Hz update rate used in multis.
*No* wag, at all?
What I'm talking about here is about 1/8".
I got it that low by reducing the rate P back down to 0.350 (I had experimented with up to 1. But, not the hold isn't as good when I jam the throttle up. I'm going to experiment with more D, see what happens.
If it's wagging imperceptibly due to control loop instability while hovering it will get worse when the airspeed in the plane of the tail rotor is high, increasing the translational lift and, thus, the loop gain.
What happens when you pull out of a steep dive? If the wagging doesn't increase you may be hitting against a resolution limit or dead band rather than instability.
I have just finished building my gas helicopter about a 90 size. I'm going to put my spare apm on it, wire all the sensors in, but not the servos, i'll use my flybarless controller CGY750, but i'll use the adapter and Y lead the from the Receiver. This way the APM will get all the inputs as i fly around, but will have no control. Its just a way of judging how the APM will put up with a spark ignition single cylinder engine at 9000rpm. I can then data log it, what should i be looking for in the Logs to see if the DCM is getting into trouble?
I flew again tonight, this time with 2.5.1.
The Loiter is much better, and does not take off on a mission due to a bug. I still haven't got it holding stable yet, and I think it's mostly to do with the fact that my heli doesn't fly level, so it always starts off loitering by going to the left and forwards (due to an aft CG and tail rotor thrust). I need to figure out how to level it better.
But, overall, this code is really really good.
So nobody liked my "Weathervane" code idea from page 117?
How are you getting on with your APM tail gyro? Is it as good as an external HH gyro?
I've never flown with an external gyro, so I can't say.
But, I'm pretty happy with it now. It holds quite nice. It's not quite perfect yet, but it's really good. I've gotten rid of the little oscillation I had. That was due to rate P being too high. Now I'm going to play with the rate D and see if I can get it to hold a little stronger.
With the coll-yaw effect, it holds pretty well when I blast the throttle too.
The only issue I have had is that sometimes when flying backwards at high speeds, the tail will sometimes suddenly jump out, like it just gives up. I'm not sure if this is a code or Mag problem, or if it's simply aerodynamics. I know there's an effect with the tail rotor thrust when flying backwards where the tail rotor almost "stalls", similar to "settling with power".
How fast is fast, most gyros will hold a tail at really high speed when flying in reverse, but only the real high end ones will over come the blow out.
I may well go back to the APM for the tail as it keeps the wiring a lot simpler.
Thanks for the update :)
I couldn't put a number to it, but I was flying backwards, not just hovering and moving backwards.
Hopefully I can get a video soon to show how it's doing. It's probably not best-in-class performance compared to a dedicated gyro, but it's pretty good.
Well, I still didn't get my tail tuned like I had it just before 2.5 (the build in source just before release), the new servo seems to quick....... but then well I was "thinking" I hit a branch.
Testing out for me, until HK sends me another $46 450 V2 :(
Back in a week or two
Yeah, I think I came pretty close to hitting some trees tonight too.
I'm reply on slightly the wrong comment in this thread but figured it better to reply near the end of the whole discussion.
In any case, sounds like you're getting pretty good performance on your tail gyro. my external gyro can't hold the tail perfectly especially in fast ascents..I'll get 45 degrees movement in a fast ascent actually although perhaps I could tune it to be a bit more aggressive.