HK 450 MT build Thread.

[vinay]

Thanks, I will look into it once Iam back from office, I think I cannot continue my build till Saturday due to office work.

[vinay]

I am back with lot of doubts 

1)FIRST

There are two schools of thought on this.

1) Separate pitch curve for normal flight and 3D flight (-4, +4, +9 low-mid-high for normal and -10,0,+10 for 3D for these types of helis).

2) Same curve for both normal and 3D flight (-10,0,+10).

I have decided to goto the 2nd school as I am very much used to flying 3D Helis on the sim. (-10 0 +10) This is done.

2)SECOND

Regarding throttle curve for normal, assuming you leave the pitch at full range (-10,0,+10) or so, you will need something like 0, 35, 50, 65, 100.  The idea is to have enough RPM for hovering around 60% (or 65%) throttle, and have enough rpm around the 30% to 40% position to land without bleeding off too much.

The heli comes with glass fiber blades and not carbon fibre blades. So can you please tell me the throttle curve in terms of RPM for a 450 size TREX? The motor is a 4000 kv and at 100% throttle and 11T pinion, it will take the head beyond 3000 RPM.  I guess its not a good idea taking the RPM above 2900 RPM for GF blades. I have done some fill up the blanks myself.

I need it for 2 modes. The hovering and 3d mode.

Mode 1)Hovering mode:
a)Pitch curve (-10 0 +10) in terms of degrees
b)Throttle curve(?? ?? 2900)in terms of RPM

Mode 2)HardCode 3d mode: I wont be using this but i want to see how this flies. So I will give it to experianced fliers at jakkur to test this mode.
a)Pitch curve (-10 0 +10) in terms of degrees
b)Throttle curve(2900 ?? 2900)in terms of RPM

Mode 3) Spare. Don't know If I will use this or need this.

Mode Hold)Hold Mode:
a)Pitch curve (-10 0 +10) in terms of degrees
b)Throttle curve(0 0 0)in terms of RPM

3)THIRD:
Any expo settings you guys recommend?

Thanks,
Vinay.

[vinay]

Vinay are you trying to level the swash plate using the RDS8000, then the below link will help you do it.

http://www.helifreak.com/showpost.php?p=766655&postcount=5

Hope this helps.

Thanks this is what I was looking for. Its what I needed to use before. But I was unaware of it and I did it manually. There is still a lot of stuff pending on the Heli Head.

Even with a leveled swashplate, the pitch on 1 blade is different by 3.5 degrees compared to another. Found this out using a pitch guage. Now to fix this 

[anwar]

Even with a leveled swashplate, the pitch on 1 blade is different by 3.5 degrees compared to another. Found this out using a pitch guage. Now to fix this 

That means your linkages are not setup properly.  Typically, except for the links that connect the servos to the swash (which will be different in length), all other links should be equal in size with their symmetrical pair ones.

Rework the linkages *above* the swash plate.

[vinay]

I am working on it. so when you say equal/symmetrical, how symmetrical should they be? will 1/2 mm to 1mm tolerance be ok?

[anwar]

As close as you can get them, is all I can say. With the Align original ones, I usually get them to be pretty much exact. If they are 1mm off, I feel that one more turn will get them closer.

[vinay]

Anwar, the heli has a perfectly tuned head now. It cannot get any better . the max diff in the lenght of the connectors is .32mm on 1 of them. I cannot change that further. Iam confident that it will fly well. Pitch is set at -10 0 +10.

I tested it in the hall keeping the pitch at 50(0 pitch, stick center) and slowly increased the head speed by increasing the throttle curve at p3(stick center.) Absoulutely no vibrations.

But I noted 2 things.

1)In rate mode - As I decresed/incresed pitch slowly, the tail started dragging left, so I should increase the gain right?
EDIT: The tail started dragging right tail-in.

2)In head lock mode - No matter what I do, The tail servo is not getting centered. It is settling at 20% rather than at 50%(center), This happens even when the motor was off. If i move the heli by hand in the head lock mode the tail blades deflect but slowly goes to that weird 20% position instead of staying at the same deflected pitch. How to fix this guy?

Its a HK401B gyro the futaba 401 clone and I have read 1000s of reviews that it is 85 % as good as the futaba, and futaba owners have started using these.

[anwar]

If you have around 50% gain in rate mode, and the tail is still drifting, then you have to counter it by mechanically adjusting the linkage length, or by moving the tail servo slight up or down on the boom; assuming you want a solid setup overall.  Or you can ignore this and fly in head-lock mode.

If I understood this correctly, what you are seeing is the proper/default behavior in head-lock mode. It will not center (unless you apply full inputs to either side quickly a few times and then let go of the rudder stick).  This is part of what distinguishes both the modes.  Try flying it with around 35% gain in head-lock mode, and we will take it from there.

[vinay]

If you have around 50% gain in rate mode, and the tail is still drifting, then you have to counter it by mechanically adjusting the linkage length, or by moving the tail servo slight up or down on the boom; assuming you want a solid setup overall.  Or you can ignore this and fly in head-lock mode.

Why adjust the link and why cant I subtrim it?

[anwar]

You would never want to put either trim or subtrim on rudder for a HH gyro. The short explanation is that the gyro learns the center every time it boots up, so it will think that the last trim you added as the center now, and will demand that much trim again.

Google it, and you can read the details.  One I found quickly is http://www.raptortechnique.com/gyroconfusion.htm and see the question "Can I use rudder trim".

It is always better to fix things mechanically in rate mode, then just flip to heading-hold and just play with the gain till you are satisfied. And the rule for gain is "as high as you can go, without causing the tail to wag".  And "wag" is quick wagging (like "shivering", not "slow drifting").

Some people do use sub-trim (not trim) to get the servo arm to be at 90degrees, but even they have to do the mechanical setup correctly.  They use it only to put the servo-arm at the right angle, NOT to counter tail drifts.

[vinay]

Thanks anwar bhai, that clears all my doubts. The heli is all complete with tail boom support fixed as well. Ready to be transported. Only problem left is to create a box for it using foam and strong coro like the align aluminium box like the link below. Got the foam in the evening. Time to build it up. Probably i will do it tom morning.

http://www.helidirect.com/trex-aluminum-carrying-case-p-1722.hdx

One last question though. The main Rotor blade holding screw has a locknut (nylock nut, which has a nylon washer at the end), Do I need to add Loctite here as well? Will loctite react with nylon washer present at the end of the nut?

[anwar]

No thread lock is needed where nylock nuts are used.

Looking forward to your maiden report     

And seeing Gaurav's flight, I am tempted to ask...  are you going to use training skids too ?

[vinay]

I will, I have 2 pairs. But Rajesh dosent need to. I hope he comes tomorrow. Or I will have to hunt for a mode 2 Heli guru.

[gauravag]

Now i a jealous of you ) You have someone like Rajesh besides you to help you during your maiden. !!

[vinay]

Well guys, some good news and some bad news. First thing, I finished working on my heli carrying case by 10 in the morning(Worked overnight w/o sleep) and by the time I got ready it was 11 30 and it was not possible to goto jakkur. SO I took my cousin and uncle to some Outside the city BDA site  and started the maiden there. It was good and drifting back words and right side and some small trims fixed them. The tail was not holding well so I switched the Gyro to HH mode and no problems at all.

Let me tell you HK450 is really a good good heli. I havent flown any in real world but Iam comparing them to the ones in the G4.5 sim. I rate it as A+.

Afte hovering for 15 mins(second battery) I came down fast and the training skid broke and the heli crashed. I have all the spare to repair the Heli except the spur gear. 

Broken parts:
1)Training skid ceneter holder broken. I need to find an alternate to plastics at the center.
2)1 X HXT900 gear.
3)Main spur gears shredded.
4)Tail boom bended(dont know hot to straighten the inward curve part.)

Iam too tired and happy that I flew the heli successfully.

I have my every heli move captured on the video including the scary crash. Will upload tomorrow.

I think, I will upgrade all the servos with the metal ones. Too lazy to change the shredded gears. Good night guys.

[anwar]

Well, congrats on the maiden 

Curious if you crashed because the lipo ran out of charge, or you brought it down too fast inadvertently.  15 minutes on a single lipo is a lot of time, for the 2200mah lipos are that usually used on such helis.

Also, not sure which gear you are referring to as main "spur" gears.  The "main gears" ?

[vinay]

Thanks anwar, w/o the help from forum, it wouldnt have been possible.

Well The first battery lasted for 8 mins and the second one 7 mins, totalling 15 mins before crash.

Well its the main gear(150 T) The motor actually bruised the main gears pretty badly and is unusable. I just ordered some more spares including the main gear. Should reach me by 16 days.

Well the crash happned I came down a little fast and the central lock of the training gear that holds all the CF rods together broke and BHOOM, in seconds it was in pieces.

And frankly, I am not disappoited by the crash at all . But it really thought me to practice more on the sim  .

[vinay]

Also forgot to mention, One of the GF blade was broken into pieces. But the other one survived with a small 1.5X1.5 mm paint chipped off, which I can tape it balance it on a blade balancer with some other similar blade and use it.

[gauravag]

Congrats Vinay.
Crashes and waiting for parts is inevitable with Helis I guess waiting for parts is actually a boon, as you get to spend some time with the SIM. I guess thats what made me hover better. Had i got the parts immediately i would have been breaking/rebuilding continuously !

[vinay]

You are absolutely right gaurav, that gives us more time on the sim. I had almost 2 sets of most of the spares. Its just because of the main gear, I have to wait. Ill start building a plane by then . and practice heli on the sim. I am also planning to upgrade all the cyclics to MG14 metal gear servos. They should be reaching me this week, most probably today.

[gauravag]

Yeah, even i upgraded to Hitec 65-MG . I guess its like an investment, but saves time fiddling with servos and replacing gears

[sk010962]

Hi Vinay congratulation on your maiden flight. Btw I too crashed mine last week after 5th battery. Waiting on spares to arrive. Bent the feathering shaft, bent tail boom, bent flybar. One broken blade.

Cause of the crash : Pilot error. Wrong input. Was trying to land in 9'0 clock position, lost orientation.

[anwar]

If anybody is considering such a heli, this is a much better design.

http://www.hobbycity.com/hobbyking/store/uh_viewItem.asp?idProduct=10902

Some of the advantages :

1) Single piece frame on each side, which means it is easier to build and maintain.  The two piece frame was one part of the original Trex 450 design that I absolutely hated

2) Lower parts count.

3) Easier mounting of servos.

4) "Chinese weighted" tails, for better tail stability/performance.

5) The issue with the canopy holder causing the frame to break is largely resolved, as the canopy holder is now attached directly to the metal main shaft bearing block.  This was a major pain, as it would cause only that one small part of the CF frame to break during crashes, but the rest of the frame was fine.

There is also a torque tube version (http://www.hobbycity.com/hobbyking/store/uh_viewItem.asp?idProduct=10901), but the belt one is better as it is much more forgiving to crashes an even tail rotors hitting mud/grass.  The torque tube version is slightly better 3D performance.

[gauravag]

Thanks Anwar,
I might be going in for one of those at some time !
HK prices do attract !

[vinay]

I saw it on the day it came out, it was still in stock and I wanted to order one, but way too expensive on crashes . So I have ordered another 28 USD wala. Dont want to spend much on the PRO till I get a little confidence. Also the spares would be expensive. Me back to sim till I get spares . Will post videos of maiden/Crashes tomorrow.