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« on: October 09, 2012, 06:50:06 PM »
dheerajjuneja
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City: Ghaziabad
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Hi,

Writing a blog like this on an iPad is not the most productive decision, however this thought that "one should not think about the medium, but the end result" got me going.

This is about my experience of building my first RC 450 ccpm heli, for people who are not sure about what 450 means here, its the class of heli (or also refered as size).

Before i go into details, let me provide some background to this:
I had bought a RTF (ready to fly) version of  450 heli, with mostly plastic parts, like plastic head and plastic tail. I opted for a RTF version because i thought i would be able to get it in the air straight away and skip the whole process of assembling, balancing and configuring various components. I was right to some extend, that yes, i was able to fly it for about 10 mins before i had my first crash due to sudden wind. This crash broke the following components:
1. Tail boom
2. Tail vertical fin
3. Tail horizontal fin
4. Tail blade
5. Flybar
6. Main gear
7. one cyclic servo
8. Flybar stabalizer

Well, the first lesson quickly learnt ( the hard way ) was that, when people say not to buy cheap RTF, they have some very valid reason. The thought that i would be in air sooner is catchy, but there is no escape from assembling, you would still have to get your hands dirty after the first crash and then one realises that what he got for the RTF was shitty electronics, third grade servos and plastic parts, which are not available easily (or cheap). My advise to a beginner is to get started with a 450 size heli, it can't get cheaper than this, and you would have plenty of support on the Internet.

Anyways, enough of the background, this got me carried away from the main topic.

So, now, I had ordered all necessary parts from HK and RcBazaar (India) and kept everything on the desk to get started fixing the broken heli. The damage was so not to intense, however looking at the parts used in the heli, I had planned to replace everything except the frame, motor, gyro and the esc.

The heli was now supposed to be having the following new components:
1. RcBazzar 450 v2 head
2. HK metal tail assembly 450 v2
3. RcBazaar main gear
4. RcBazaar tail boom
5. Avionics AV9257 tail servo
6. RcBazaar landing gear
7. Turnigy TGY 1800A cyclic servos
8. RcBazaar tail fins (CF version)

I started with the tail, took out the boom, carefully taking out the belt from the gear. Removed the plastic tail assembly and all removed everything from the tail boom. I then took out the new tail boom and fitted the tail assembly on one side, and managed to get belt out of the other end of the boom. Everything looked nice with the new tail assembly metal version instead of the black plastic.

That Tail:
------------
1. When fitting the tail servo, I fitted the new servo in the same place as the old servo. This was not the right approach, I should not have tightened everything before checking the tail link rod adjusting properly. I had to flip the servo horizontally to get the link rod fit nicely, I could have saved 10 mins by first connecting the link rod and then putting the servo.

2. The second issue I faced was that once everything was in place, when I tried to slide the boom into the socket, the belt would not reach the gear. What the hell, I thought it should have fitted properly, but no. Upon investigation I realised that the boom was slightly longer than the original. I said, man, what is the RTF. Anyways, I had to cut short the tail boom by around 2cm go get the belt fit nicely.

3: Third issue, the nose keeps drifting towards the right, no matter what i do. This is what I had already tried:
A. Aligning the servo to centre: by keeping the endpoint settings in the radio to 100%, removing any trim (and subtrims) settings applied to rudder, placing the servo arm at 90% angle to the tail boom, adjusting the link rod length etc so that the tail blades are perfectly straight. Result: tail drifts to left, even at 100% gain (hh mode) there is no tail wag.
B. Upgraded the tail servo, tail assembly, this time I adjusted the tail link rod length so that the tail blades have a 1degree angle. Result: tail drifts to left, no tail wag at 100% hh mode.
C. Tried both the above with rate mode, and switched to hh mode only when I can hover with very little rudder input in rate mode. Result: less tail drift, but the tail still drifts ( see the video )

Ok, finally i fixed it, at times when you fix something you think, man it was such an obvious thing, why didn't i thought of it earlier. Anyways, the solution was to increase the head speed.

The head speed was increased by increasing changing the throttle curve to increase the throttle %age:

Old values (graph point - output value)
0%       0%
25%      25%
50%      50%
75%      75%
100%   100%

New values (graph point - output value):
0%       0%
25%      35%
50%      65%
75%      85%
100%   100%

* Don't forget to lower the pitch degree very slightly, while increasing the throttle pitch, otherwise what would happen is the as you have increased the head speed, the heli would be able to lift off at slightly less pitch as well, and would nullify the whole purpose of increasing the throttle curve.

The main gear:
--------------------

Replacing the main gear became necessary as a very small portion got effected by the crash and the gear started to make some uneven noise, which started distracting me. Replacing this gear should have been easy, but this thought me another lesson.

Though I had replaced gears in my walkera 1#a, but this was different. The gear in 450 has to attached on the autorotation gear from a particular side. If you attach it from the opposite side, you would be able to fit everything back ( like I had done ), however, it will cause the gear to wobble up and down, or it may cause excess noise and pressure in the whole system.

Initially I thought there is something wrong with the gear I had received, however, that was not the case, on careful inspection of the gear I found that both the sides were different. One was flatter than the other, which had some grove in it. So, once I flipped the gear, it became very smooth.

The lesson is that the side with the additional depth needs to face the head of the heli (it would be facing upwards).

Not very responsive tail:
------------------------------

The tail was not very responsive on the inputs i gave on TX, so this is what i did:
1. The additional head speed did make a slight difference
2. The major change came when i CA'd the servo to the servo holder, along with using the screws i.e. I applied the CA on the flat surface just next to the screw holes, this is the surface that comes in contact with the servo holder. This made the contact with the servo holder very strong and there was no movement of the servo up and down when the rudder input was given. This translated into pushing all the force to the rail assembly and making the tail very responsive.

-- To be continued (feel free to give your inputs on what problems you faced and how you solved them)
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« Reply #1 on: October 09, 2012, 07:18:30 PM »
saikat
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Did you have anyone to teach you?  How long did it take you to hover?
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« Reply #2 on: October 09, 2012, 07:25:26 PM »
dheerajjuneja
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Did you have anyone to teach you?  How long did it take you to hover?

Hi,

Learnt mostly from this forum, YouTube videos and ebooks. I was able to hover in sim very quickly, but my first hover on the real heli was about after 2 months when I came into this hobby, which was around 6 months back.
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« Reply #3 on: October 16, 2012, 04:53:57 PM »
dheerajjuneja
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City: Ghaziabad
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Heli Wobble on spool up
---------------------------

Six important things:
1. Take out the head, just let the tail and main shaft spin, is the wobble there? If yes, check your tail shaft and main shaft etc
2. Is the main shaft true i.e. it should not have any wobble when you run the motor without the head (only the main shaft attached)
3. The flybar should be dead centered i.e. it should have exactky equal length from both end, plus the flybar paddles should also be balanced.
4. Are the blades balanced?
5. Have you done the blade tracking?
6. The main blades should be tight enough that they don't move in the balde grips, if you hold the heli in your hand and tilt it around.

I would start with taking the head out:
-> Check if shaft is fine
-> Put the flybar and ensure its equal in lenght from both end
-> Attach the paddles and spool up to check if there is no wobble with just the flybar
-> Attach the head and spoll up to ensure that the head is balanced (very rarely the head can be un-balanced)
-> Then attach the perfectly balanced blades + do the blade tracking, tighten the blades properly
-> Then see how much wobble i have left with.

-- If wobble still exists, get help from this forum
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