The official 600 stretch mod thread

[R_Lefebvre]

Did the frame cut last night, and started the anti-vibration mount work. So far so good...

[338federal]

Hi! I have Align 600E Pro and 690mm radix blades. Does the the head hold the load from this heavy blades and what is the maximum rpm? Now the blades are spinning about 1750-1850rpm. I have problems with vibration but i try tomorrow with new dfc head.

[runesb]

K6-800 Maiden 21032013 - YouTube

K6-800 Maiden 21032013 - YouTube

2nd flight

K6-800 2`nd flight - YouTube

K6-800 2`nd flight - YouTube

[Feeback]

Very cool!

[R_Lefebvre]

I'm finally getting close to finishing my 550/600 UAV heli, fired up the avionics last night test it out. The 2S LiFe pack for the avionics doesn't seem like it's going to work out well.

The problem is that LiFe has a super flat discharge curve. Full charge is 6.6V, and it's done by 6.4V. In some ways that's good that it has a flat curve, but detecting battery condition relative to voltage is hard. Making it harder is the fact that it seems this LiFe pack can't deliver much power? It's a 1700mAh, rated at 20C. If I stir the cyclic stick fast to make the servos dance, the voltage drops from 6.6V to 6.3, and sets off my voltage alarm set for 6.45V. I'll have no end of false alarms unless I set the alarm level way below the recommended voltage level for the LiFe?

Anybody have any ideas? Am I missing something?

One of the main reasons I decided to go with LiFe is because I am using a super fast HV servo on the tail, but it doesn't seem happy with a full 8.4V. On 7.4V it's fine, but on 8.4V it acts like it's overgained. So I figured LiFe 6.6V was a good way to go but... doesn't seem this is going to work out.

I've never used LiFe before so this is my first experience with this.

[R_Lefebvre]

I went ahead and changed back to a 2S LiPo for the avionics, and had to change the tail rotor servo so a slightly slower one that works with 8.4V. (0.06 sec/60).

Finished building the heli:



Obviously the wiring looks a little "busy". But it has a lot of systems on it. Full autopilot, telemetry, and LED lighting. Here's where I cut out the central frame to make a place for the main part of the avionics. This is the APM controller, with my own daughterboard installed on top. This contains a de-cased FrSky D8R XP receiver with telemetry. The APM has it's own telemetry system which is the antenna sticking down from the boom supports. The LED lighting is controlled by the APM, it uses it for some status indication.



Took it for some test flights yesterday and it went very well. The only serious issue I had with the heli was I stripped out the tail drive gear (the one driven by the autorotation gear. There's not enough engagement between these. So I had to remove the tail and slot the boom mounting holes to be able to move the gears for a tighter mesh.

[R_Lefebvre]

So is there any easy way to stretch this to 700? I've got a 700 tail boom already, and I think I just need a longer belt. Is it available? I've seen talk about using a wider belt, which then necessitates a different pulley... is that the only way?

[runesb]

Hi man. Cool build of yours.
No problem to strech to 7, ditch the belt and use tt. Less work to fit. If you use stock boom mount some filing to make tube to fit in gear. Or extend the tt.
Rc tek boom mount, require even less work to fit the boom and no mod on tt

[R_Lefebvre]

Yeah... I'm really not a fan of TT. I had it on my 450 and hated it so converted to belt. Maybe it would work better on the larger machine. I don't have to worry about tail rotor strikes much because of the massive stabilizer I made.

But, what I really want to do is go to a direct drive tail. Dedicated motor right on the tail. So if there's no easy way to do a belt, I'll just wait until I can get that working.

[runesb]

I dont like the tail belts, but thats me.
The problem with motor on the tail itself is the weight. If you can hold a good cg with the weight of the motor, just start to make the mod and give it a shot

[R_Lefebvre]

Well, there's going to be a camera on the front, so no problem with CG. If anything, it's actually very helpful to have the weight back there.

[runesb]

Just start the mod and build

[R_Lefebvre]

Time and money man, time and money...

[runesb]

Do realy know what you mean

[R_Lefebvre]

So far things are going VERY well with this heli. I was a little skeptical that that the FBL would be more stable than the Flybar. But there's little question in my mind now. It's just an absolute rock in the air. I have yet to fly it in 40 km/h wind like the last one, but 20 km/h is doing really well.

I've had it up to 122 km/h so far. Not too bad. I don't really have enough room to go much faster though.

I also have a problem with pitching up and "porpoising" at high speeds. Also the tail gain is too high at higher speeds. I have to figure out how to manage this. Not sure how all the other FBL controllers handle it exactly.

[runesb]

Set up lower tail gain in iu1 or 2 in your tx.

[R_Lefebvre]

Yeah, I could do that, but I'm considering having the controller do it automatically based on ground speed from the GPS. Lower the gain. Fairly easy to do, though I wish I had a true airspeed sensor.

I would really love to know exactly what "Pitching Up Compensation", or whatever the various FBL controllers call it, are doing. Like, what they're REALLY doing internally. There's some aerodynamics going on here that affect this, and obviously they've solved it, but without having any sensors that tell the FBL how fast it's actually going so, I don't get it.

[martin_]

I would tend to say that there's not much flybarless unit that can completely correct for pitching up in high speed, some are better than other but if you have a particular mechanical set-up/blade that is prone to pitch up easily, then there's not much you can do.

A good set of heavier blade will do much better than any setting, or if you can introduce some delta in your blade grip link with soft dampener, this will also help, however you will feel the stick a little spongy/delayed on command, not good for quick maneuover, but if you don't care.

Too much collective pitch make it worst also, so you'r better with higher rotor rpm and less pitch for high speed.

The parameter to adjust seems to be the heading hold gain for cyclic or the I part of the cyclic PID, but I find it to be only reactive to the issue rather than preventing it.

I have experimented a little on this subject, and this is the best I've found, hope this help.

[R_Lefebvre]

Thanks Martin. So when you say "pitching up", you mean an oscillation, like a porpoise or dolphin? Or just blowing back once and coming to a stop, potentially after having eased forward pressure?

So softer dampers may help? I'm already fairly soft, but I think there's one step softer I can go.

So how do guys get TDR's up to 200+ km/h?

Part of the issue, I think, is that the condition this happens the worst is flying around in Altitude Hold mode. That gives control of the collective to the computer. It's extremely responsive, and can hold the altitude within inches in any wind condition. But I think it may be too responsive at high speeds. The heli drops just a tiny bit, maybe due to a tiny pitch error, and it responds by adding collective. At the same time, the pitch controller pulls back a bit to fix the pitch. Both controls together cause an over-reaction, so it shoots up, and they both over-react coming down too. Can get into a really violent oscillation.

It's a difficult control problem.

Anyway, I've mostly been interested in what the other FBL controllers do exactly. Is it some kind of manipulation of the rear swash servo?

[martin_]

Hi Rob, no there is no control of the rear servo, this is ''heading hold'' on cyclic, and all 3 servo work together.

The worst scenario I experimented were an T-rex 550 with edge 520mm fbl blade, at full speed/full collective the heli was not going in a straight line, it was moving in an arc (nose up) a normal FBL controller have no way to catch this, I then tried other blade brand in 550mm size and that behavior was much less, but still there a little.

Other issue is while at high speed when you move collective up-down the nose pitch up/down also, some controller are better than other at controlling this, since it's a sharp movement, the gyro can sense it and correct it. From what I have experimented, the BeastX is very good/smooth at this.