How do I know if my tail servo is really faulty?

[FyreSG]

To keep the story short and simple, I collected my 450QS from the shop and took it for hover training. All was ok until the tail servo suddenly stopped working. The heli yawed uncontrollably and plunged into the ground. Luckily, minimal damage was done. I called the shop who fixed the heli initially. He told me he had performed a test flight before confirming the tail problem was fixed. He had determined the tail bearings were worned out and replaced them. Yet after being repaired and passed the test flight, another tail problem occurred. Now, he attributed the fault to the tail servo. As installing a new tail servo is costly - in terms of monetary cost and man effort required to setup the tail + gyro all over again, I'd like to know how I could confirm if the tail servo is really faulty, that caused the tail to suddenly go crazy only in midair. Another potential culprit could be the gyro but he felt the likelihood of a failed servo is higher than the gyro. Any ideas? Thanks.

[FyreSG]

Wall of text?!

For some reason, all my individual paragraphs were all combined into a wall of text! Sorry guys.

[feudallordcult]

can use the "lemon law" in this instance? Yr description pretty ambiguous. Type of servo & gyro? with regards to amount of man hours invloved to rectify the fault & setup, that's not yr problem to begin with.

[FyreSG]

It's ambiguous because I left out the looong story. I don't wish to go back to the shop for this issue because it will take up more time and money. As long as I can confirm the fault lies with the servo, I'll be satisfied.I'm just worried that after buying a new servo and performing tail setup, the tail still goes crazy in midair.

[MicroHeli-Nut]

dismount all tail blades and main rotor blades.

Spool up to 50% throttle ( in a safe area) , move all rudder and cyclic (with heading hold on)

check for erratic servo movement....

Spool up to 70% throttle.

( I'm unlicensed, but this is how I test- with safety googles on, away from screens, flammable objects and sharps)

Regards,
Ray.

[FyreSG]

Here comes the full story of the crash

Thanks for your inputs and also thanks to the kind bro who PMed me! ;)

I should have provided more details on the crash. Here goes!

First hovered at knee height for 1 minute. OK! Landed the heli and checked. Cool! It's time to progress higher.

Then I hovered at eye level for 1/2 minute. I noticed blade tracking was off so I landed it and adjusted the linkage rod. Hovered again for 1/2 minute, realised the adjustment was too much, so landed it again to fix blade tracking. (I don't think the linkage rod tweaks caused the crash).

I hovered it again at eye level. After 1 minute I think it feels fine, so I sent it forward and backward for about 5 metres. Nice. Then I kept it at eye level because I just wanna "admire" the sight of my helicopter (sorry, I know I'm lame) hovering. Then the tail went crazy and my instinct flicked the throttle hold.

The helicopter actually landed on the skids! The main rotors hit the ground with one blade tip scratched. The aileron and pitch servo arms were off centered and I will need to unscrew them to realign.

Right after the crash, I inspected the helicopter. The tail servo is "dead" - moving the rudder stick doesn't move the tail servo. The gyro red LED also doesn't blink (usually when I move the rudder, it blinks). The gyro LED just turned red.

I disconnected and reconnected the battery. The tail and gyro came back alive.

So that's basically the recent crash episode. The story of my earlier tail failure that led me to send it for repairs, well, I'll save it for the next time.

[FyreSG]

Good idea

dismount all tail blades and main rotor blades.

Spool up to 50% throttle ( in a safe area) , move all rudder and cyclic (with heading hold on)

check for erratic servo movement....

Spool up to 70% throttle.

( I'm unlicensed, but this is how I test- with safety googles on, away from screens, flammable objects and sharps)

Regards,
Ray.

Many thanks and suggestion noted!

At 70% throttle, my heli would lift off the ground. I suppose I'll change the pitch so that at 70% the pitch is -0.5 or -1.0 degrees. It seems safer that way. Or I'll put back the "orange balls" training skids and hover it at knee level.

Judging at the super high failure rate of my 450QS, I only hover it at the Queenstown flying field.

[MicroHeli-Nut]

read the whole list... you are supposed to check without blades on...

[FyreSG]

Oooops! Side effects of a heavy lunch.

[feudallordcult]

methinks u go back to the shop and ask them do a good job. Thats what I would do.

[foxkilo]

FyreSG,

What tail servo are you using now? Some of the "clone" brand tail servos are quite unpredictable in quality. I've had a GoTeck tail servo fail on my 450 Pro clone just after a few flights... if you want to confirm servo failure, try to move it by hand and see if the gears are still nice and smooth.

After replacing the GoTeck with Align DS520... no more problems (touch wood!), and on the same gyro, setup, etc. I have another two 450 helis - a Mini Titan v2 with Savox tail servo, and a 450SEv2 clone with good ol' analog Hitec HS-81 (!) tail servo - and no problems at all too.

The boom/tail components on a heli are very important, and it's best to use original parts and "branded" tail servo for precision and reliability - even if the rest of the kit is "clone".

[FyreSG]

Another Story

Seems like maybe I should write the full story. Here goes!

Previously, the helicopter tail had an "unknown" that the heli spun widely even before lifting off. I sent it to a shop for assessment. The guy examined it and found the tail bearings to be worned out, so he changed it for me. I paid 30 bucks for the bearings and the labour charges.

When I tested it the first time, it was ok. When I tested it the second time (the above story), then it went crazy. Several possibilities here - maybe the bearings were not the culprit; or maybe they were? Maybe the servo intermittenly fails? And/or maybe the gyro intermittenly fails? I really don't know. The fault didn't show up readily so I worry that if I sent it back to the shop, the fault may not show.

I'm not sure if sending the helicopter back will be a good idea. Firstly, I'm afraid that he may simply tell me to change both the gyro and tail servo. That would not be economical. My tail servo had been upgraded when I first purchased the helicopter, because he convinced it was "necessary" as the stock one was "no good". (But hey, that's not important now.) That high-end tail servo costed me $40 (even though I just need a heli for hovering training). If I were to replace it again, and along with a new gyro, and include labour charges... I might be better off buying another better helicopter.

I have learnt a lot since the day I bought the helicopter. I suppose these costs are the "school fees". I think it may be better for me to fix the helicopter myself. I get to learn and save money. The sad thing is my teachers at the ECP flying field are gone... I actually picked up most of my knowledge there.

[foxkilo]

How "high end" is the tail servo? Maybe you can give the brand/model number? Gyro too?

Learning to setup on your own is not too difficult, and better for the long-term. There are excellent video guides on helifreak forum by this guy "Finless".

[FyreSG]

Stock: KDS 9G





Upgraded: KDS N590 Digital Tail Servo

• Digital servo
• Speed: 0.08/60 4.8V 0.07/60 6.0V
• Torque: 2.0kg/cm 4.8V 2.5kg/cm 6.0V
• Operating frequency(Hz): 300
• Dimension: 35.5mm x 15mm x 28.6mm
• Weight: 25g

[FyreSG]

KDS 820 Gyro

KDS 820: http://www.kdsmodel.com/index.php/site/products/id/23

KDS820 is a gyro with function of dual rate & head lock, specially designed for helicopters. KDS820 adopts AVCS(Angular Vector Control System) which makes the function of head lock more outstanding and steady.


AVCS system: Since rudder trim changes caused by wind and other meteorological changes, and varieties of helicopter attitude changes are automatically cancelled, tail rudder operation becomes easy, making it perfect for 3D flight.

KDS820 specifications


Control system: digital proportional integration sysytem
Sensor: SMM
Operating current: 30mA
Operating voltage: 4.8V~ 6.0V
Operation temperature: 0~ +40

Dimensions: 28 x 28 x 20 mm
Weight: 25g