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.
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Hi all, i have been off the topic for a while as the weather is not too good and i'm a bit of a fair weather flyer.
My heli has been rebuilt, tonight i'll load the code, it looks as if i have a load of reading to do from here.
malc
Well, I made a bit of progress on my issue.
I played around with some capacitors for a while to try and filter any noise on the powerlines. I robbed a couple big ones from an old video card. I put 1500uF on the 11V supply to the servo, and 3300uF on the servo rail of the APM. At first I thought they were making a difference. (do they need inline resistors to really act like a filter?)
What I quickly realized was that the issue is 100% determined by the location of the Xbee antenna. Moving the Xbee around, I can completely eliminate the problem, or if I point the antenna at the servo or servo wire, it goes totally nuts. I may be able to keep using this servo if I am careful.
I'll probably replace the servo wires with twisted triad wire. Move the big cap to the servo end (but honestly, I suspect the interference is coming in the signal wire). And find a really good place for the Xbee. But I'm not sure where that is yet. I had it mounted on the side of the frame near the receiver battery, UBEC and tail servo power wiring. The other side has the ESC on it, and I sure don't want to mess that up. I may position it on the bottom of the frame with the antenna facing straight down.
Not sure why it changed mid flight. But it could be as simle as the Xbee antenna being moved by a gust of wind. The interference is REALLY sensitive to the antenna position.
Michael Oborne has released 1.0.95 of the mission planner including an improved heli set-up screen.
1st thing, this new screen only works with the latest version of the code that I've just checked into GIT. if you try to use an older version of the code, you'll see an error message.
I also removed a couple of bugs from the swash set-up code and throttle scaling. Please give it a try and tell me if you see any issues.
As a reminder of how the above screen works - to set the travel of the collective:
1. push the center "manual" button to allow the swash to move freely
2. use the collective pitch to move the swash to it's min and max.
3. move the collective so the main blade pitch is 0, then push the "zero" button
4. finally push the "save" button again ("manual" will have become "save") and check the swash travel is as you'd like
5. if you don't like the results you can push manual again and manually type in min, max and zero values referring to the value printed below just "Collective".
Setting the rudder travel works in a very similar way.
One thing I have noticed is the roll and pitch reaction to your input becomes less as you shrink the collective's travel. Please tell me if this is good or bad. One solution is to increase your roll and pitch PID values to counter-act this..
I have a problem with the current code from the GIT. The collective, pitch and roll of our heli is limited but when in CLI the movement is okay. Any ideas?
After all the testing I did yesterday, it looks like I'm going to have to abandon the 3S servo. I can't figure out why it's doing what it's doing. Bummer. I don't even think I can use it for a camera gimbal, because it appers like any channel it is connected to causes the problem.
So far it appears the only part I don't have is the sleeve that fits on the main shaft where the one-way bearing rides. But I can make do with this one for now I think.
The more I think about it, the more I think the issue has something to do with the the fact that tail servo is running off the battery direct, and the rest of the system is running through the UBEC power supply (switching type). It's a 5 amp unit which I assumed was enough, but I wasn't paying enough attention and never saw anything discussing it. Possibly it's approaching the 5 amp limit so the voltage is dropping, not enough to cause a true brownout, but enough to cause the signal to the tail servo to drop, such that the signal recognition is coming in and out. The fact that it's switching unit may also cause electrical noise.
I've ordered an 8 amp SBEC (linear) power supply and I'll see if that makes a difference. This will be a bit tricky, because the SBEC is only rated at 7.4V, and the servo needs 11.1V. Apparently the SBEC can run on 11.1V at least long enough for me to run the test before overheating.
Tonight I'll try recharging the battery and testing again, maybe there's a chance that had an effect, though it was at 90% I believe. But it's worth a shot. I'm still trying to figure out "what changed" mid-flight.
Well, I just came back, flew about 75% of 1 pack... The heli took a dirt nap. Luckily the battery ejected on impact which saved it from doing the funky chicken. Damage doesn't look too bad, well, it's bad, but not as bad as the last crash. So far I can see tail boom, 1 tail support, flybar, main blades and landing gear. Luckily the main pack I had on board was the one from the last crash, so I didn't damage another pack. This one looks like the cells got bent a bit, I bent them back straight, they're undergoing flame testing outside right now. ;)
I'm not exactly sure what happened yet, I put it in Loiter mode at about 20 feet, and it climbed to about 50 or so. I was struggling with the Alt_Hold all morning. It just seems the baro is hopeless at controlling a heli at 20-100 feet. Weather conditions are heavy overcast with about 20km/h winds gusting to 40km/h. The heli flew great in stabilize, but it just goes all over the place in Alt_Hold. And you can see it on the APMP with the heli sitting on the ground. The altitude is not stable. I'm no atmospheric guru, but is it realistic to use air pressure control within the range of 50 feet?
Anyway, I decided to put it in GPS hold at at least 20 feet, it climbed a bit, but was actually holding GPS somewhat against the wind. Not bad. Then all the sudden it started yawing. My brain thought it was because something in the Position hold, so I switched back to Stabilize. It was now nose-in. I think I tried to yaw it around to be tail-in again, when it just started spinning again. Something like that. I'm not sure if I ever really regained tail control at any point. Anyway, it was spinning around about a 1/4 turn per second, and I'm trying to control it but it drifted away into the ground.
I don't yet know what the root cause was. Powered up, post-crash, the tail servo seems to be funky. It has like a rythmic thrumming. It vibrates at about 10hz in a small range, and then about once per second it gives a flick. I'll try to track down the root cause, either APM or servo failure.
I think I have everything I need to rebuild, except but I don't know if I have main gear. :(
In the meantime, the rest of the flight was going reasonably well. I got the tail working pretty well, and it was heading-locked quite well with no stick input required. That really helped so I could work on the altitude hold. I made some improvements on that, but I just don't know what hope it is when you can see the altitude moving all over the place when the heli is sitting on the ground.
I have a question about Alt_Hold. The Quad wiki page says that you can gain or loose altitude by moving the stick up and down. When you enter Alt_Hold it uses the current throttle as a base point. OK, that's fine. But when in Stabilize, my stick is above center. The center of the stick is zero pitch. So I need a bit of up just to hover. When I flick it into Alt_Hold, do I need to then center the stick so that it is not receiving a climb command? That's tricky because the throttle stick has no center. So I'd have to look down at the stick. Or am I supposed to just "feel it" by looking at what the heli is doing (climbing or falling?)
I flew through 2 more packs today. I went to a local baseball diamond that was fenced in, gave me a bit more room than my back yard. Conditions were pretty breezy, 20km/h, gusting to 30. I almost didn't go out, but it was actually easy. Helis are pretty wind resistant. The only real issue was the gusts changing the transitional lift could make it go up and down even under manual control.
I thought it was pretty cool, sitting there with my netbook, connected to the internet via my Android phone as a wireless hotspot. Had APMP open with Google Earth showing my location. And an Xbee connected to the heli so I could play with the PID values without having to walk over to it and plug a wire in.
B-)
Yeah, I got an Xbee over the past week, set that up. Fairly easy other than the wiki is a bit of a mess. I'll try to fix that. Also, the official kit doesn't come with the right pin headers, not sure what's up to that. I had to steal a pin header from a Turnigy tester driver I had sitting around... Otherwise, piece of cake. I put the ground station unit in a nice little project box. Looks slick.
I found that the acro mode seems to be pretty much useless for me. I'm not sure if it's because I have a flybar, or the code just doesn't work, but I find that if I reduce the AcroP term enough to get rid of the death wobbles, then I have no authority over the rotor disk at all. I can't even stop the wind from blowing it around. If I increase the P, the death wobbles come back. I've got the I term zeroed, maybe it needs some? Normally I zero the I-term and just work on the P at first. Eventually I just gave up because it was actually dangerous.
I also tried Alt_Hold. I had way too much Throttle_Rate_P at first and it was blasting up and down. Reduced that, it's still a bit bumpy, I have to keep working on it. I am a little confused about ThrottlePID and Alt_Hold PID. Which does what exactly. I'll go back and re-read what Randy wrote, but I'm not sure I get it. I got most of the jerking out, but it doesn't hold altitude well and I should have been in sonar range. It's entirely possible it needs a lot more Throttle_Rate_I. Or is it Alt_Hold? Basically it was going up and down slowly about 10', and also bumping up and down about 1" within the wider range.
I tried Loiter briefly, but it started to wander and I didn't have enough space or good enough altitude hold to just let it wander and see what it would do.
Overall, pretty good day. I'm getting closer. I should be able to give it a shot for the T3 challenge.
The tail control is not bad. It was waving back and forth a bit, so I reduced the P term about. But it's not locked in as well as I'd like, in terms of heading hold. I have to constantly be on the stick to keep it facing the right way. Maybe it needs more Stabilize_Yaw_I?
@Randy:
Really? It sounds like you're saying that the throttle (or collective pitch is really what I'm talking about) isn't scaled in stabilize mode? How could that be? I thought we set the max and min collective pitch in the setup, and that's as far as those servos can move in ANY case, no? Because I have bad servo binding at true max travel.
Wouldn't this cause the I term to wind up? I'd think it would overshoot badly at the end of an altitude change. Could be really bad if you're descending close to ground.
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