View Full Version : V120D02S Faulty Gyro?

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02-22-2012, 09:11 AM
Hello, I've been trying to learn to fly my new V120D02S with very little success.
The problem is that the gyro seems to have a mind of it's own and not in a good way!
I've made a video to show you what I mean.
With all the TX settings as per the manual and the elev/aile gain pot in the 10.30 position, when I advance just the throttle stick, the swashplate is getting pulled down at an angle, most times to the right hand side. When I close the throttle, there's a small delay and then the swash pops back to the level position.
If I turn down the elev/aile gain pot to zero, the swashplate says level as I apply throttle.
The weirdest thing is and what I've also shown in my video, is that if I bind with the heli battery on first before the TX (the opposite way to normal) the problem is still there but is greatly reduced.
I've asked the same question on another forum but I've had so many confusing answers, even one that said that this is normal behaviour for the gyro.
I don't see how it can be because with the heli flat and level on the table top, the gyro shouldn't be moving the swashplate to extreme angles should it?
Anyway, it's pretty much unflyable because it will either flip right over on take off or if I do manage to get it off the ground, it will then shoot off in any number of directions out of control.
Does anyone have any ideas please?

02-22-2012, 08:24 PM
Yes, this can be normal. Your gyro is seeing vibrations as tilt. This is normal when the bird is taped down, held down, has no blades, etc. This doesn't happen in the air, as the heli is free to tilt however it wants. In the air, it will actually be able to tilt, so the gyro doesn't have to overcompensate. That's what is happening on the ground. Most likely, due to vibrations, etc., the gyro is trying to tilt the helicopter in what it thinks is the right direction, but since it's on the ground, it senses that it isn't moving to correct the issue, so it keeps on tilting. Once you get it airborne, it should fly normally. The gyro isn't meant to be stuck on the ground, so unnecesary behavior is likely. Hope this helps to clarify things.

Have you tried to fly it yet?

02-23-2012, 08:15 AM
I have tried to fly it. Most times it will roll over and flip into the ground on take off. Sometimes it will take off fairly level and then want to roll over or dart off in one direction.

I was searching this forum and this guy sounds like he has/had a similar problem.

02-23-2012, 11:03 AM
Mine did the same type of thing when I spooled the heli in my hand. I also had a severe tipping problem when trying to gently lift off and fly. However, all these problems went away when I decided to break the "rules" and connect the battery in the heli before turning on the transmitter. Assuming your transmitter is set up properly, try plugging in the heli, setting the heli on the ground or launch pad, and then turning on the transmitter. I'll bet things go better when done this way.

02-23-2012, 11:22 AM
Hi, like I wrote earlier and show my video, with the RX battery on first, the problem isn't as bad but it's still there.

I've spent a few hours now reading through lots of old threads and I think it maybe due to vibrations effecting the gyro. The whole heli does shake as I spool it up between about 5% and 20% throttle and then it smoothes out. It was like this straight out of the box so I just assumed it was normal.

02-24-2012, 11:52 AM
"...Most times it will roll over and flip into the ground on take off. Sometimes it will take off fairly level and then want to roll over or dart off in one direction."

Do you know anyone with flying experience that could give it a try???

The description you listed above sounds exactly like me trying to hover for my first week or so.

What are you D/R, Expo and T/P settings set to? If you have the sticks set too hot, this thing can get away from you really really fast.

Also, regarding the shake during spool up, check all the gears and the topside of the main gear for broken or damaged teeth. low RPM vibrations are usually gear related (eg. broken teeth), high RPM vibrations are usually bent shafts, bad bearings, or balance issues.

02-24-2012, 12:52 PM
Another thing to check is the setup on the collective servos, swashplate and rotors to make sure that at half throttle/collective, which should correspond to 0 ptich, the servos are close if not exactly at the center of their travel, the swash plate is level and the the rotor blades are indeed at 0 pitch.

I had the same situation with my V120D02S and found the collective setup way off. That and the thrust ring not positioned/tightened to hold the main shaft in a fixed position vertically.

Testing the thrust ring is easy, hold the frame of the heli firmly in one hand and with the other, try to lift up and push down on the rotor head and if it moves at all, the thrust ring needs to be moved closer to the bearing surface, but not too tightly so as to cause excessive wear on the bearings.

That said, not only will vibrations confuse gyros but their trying to work against something other than gravity, being fixed in place, will cause problems but there is also a 'ground affect' component that will confuse things even more.

I've seen 'instructional' videos where the presenter suggests to adjust the trim so that the heli takes off vertically which to me makes no sense because how a heli performs near a surface is nothing like how it performs in the air.

That said, while I don't think a test of the bird when held in place is that useful, your actually trying to fly it and it going off the deep end says a lot more.

But again, if you haven't already, check the mechanical setup to see if it is as it should be as well as make sure that the collective servos are even connected to the right ports on the receiver by making sure the servos act reasonably to stick movement.

02-26-2012, 02:25 PM
I'm a much happier bunny today.
After countless hours of trying to solve this problem, I think I've finaly cracked it.
Yesterday, I took the thing apart and checked everything, put it back together and it flew the same way as before i.e. eratic!
I then took a close look at the way the RX was mounted and noticed something. Out of the box, the back of the RX was tight up against the elev servo. You lovely helpful people have already opened my eyes to vibration problems effecting the gyro etc so I changed things to see if it would help.
This is how I've mounted it now. A picture shows it better than I can describe it. Basicaly a softer foam was used and cut so it doesn't touch the gyro (I think it's the gyro!) and I made sure the back of the PCB with the connector sockets was NOT touching anything.
The difference this has made to how it flies is astonishing. Maybe the gyro on my RX is ultra sensitive for some reason. Now if I can just eliminate more of the heli vibrations, it will fly even better I'm sure. At the moment, I can't take it any higher than about 10.30 o'clock on the gyro pot and about 60% on the TX otherwise it starts getting eratic again.
I've also moved the ESC to the other side so that the cable does not cross over the RX and add to the vibrations. I read that the heat from it can effect the gyro as well but so far so good.
Phew! steep learing curve for me coming straight from flying an MSR for a few weeks.

02-26-2012, 02:49 PM
Another modification that I've done.

The tail on mine seems to be very flexible. I can twist the fin from side to side very easily and in flight, the torque of the tail rotor blades was twisting it around. I don't see any cracks in the boom and it's been like this since day one but I'm sure it's not correct.

So anyway, while I wait for a new boom just to make sure, I installed this mod and it works great. It's just a bit of steel rod which I bent the ends into loops. I then drilled a hole in the tail fin and screwed it together. Very light but quite stiff and no more tail twist.

Oh yeah and on the end of the tail fin, I've glued a section of rubber tube, cut down one side because the sound of that carbon fin hitting the deck on each landing was giving me a heart attack!

02-26-2012, 06:16 PM

As mentioned in another thread, my Mini and 02S also have 'flex-tail-itis' and they too were that way from day 1. I hadn't noticed a problem with them being that way though.

But, seeing what you've done makes me want to try it to see if they fly even more smooth than they do now.

It would be hard to believe they could fly any smoother but if it improved your flight characteristics from bad to OK or better, it will hopefully have an even more positive affect on mine.

On a related note, after putting my 02S back together again, I tried to fly it and it and I couldn't even get it off the ground, it was so shaky. What I found was that I hadn't tightened the screws holding the rear vertical fin and it was flopping back and forth a little causing rapid changes to the air stream. Tightening up it fixed that but still, it showed me how sensitive things can be because it really wasn't all THAT loose.

Out of curiosity, what was the source of the steel rod? Anything commonly available?

02-27-2012, 04:28 AM
The rod is the antenna from a cheap RC car that I had lying around..

02-27-2012, 07:32 AM
Ah, so not readily available.

I'm wondering about doing something like that on my 02S but instead of running it from the horizontal stabilizer back to the vertical stabilizer, run it all the way to the tail boom support mount points on the skid.

The wire wouldn't necessarily have to be so stiff then as it would effectively be acting as 'guy-wires'.

I'm not sure that won't become a grass catcher though causing yet more problems.

Still, a very good idea on your part! :clap

02-27-2012, 08:01 AM
Just a heads up-- I've had 2 V120D02S. First RX I did not have any problems at all. I could hold the heli in my hand and spool up, zero servo creep. My second one had chronic servo creep. After eliminating all vibes (I never had a smoother heli!) the creep was reduced, but was still there. It became apparent during hovering as without any cyclic input the elevator servo would pull up, so in hovers it would eventuall start to fly backwards-- as soon as I touched the cyclics it would reset.


04-01-2012, 12:05 PM
Are your swash settings "1 servo-Normal"?

I hope that's not a dumb question, but I didn't see the answer in your settings.
With a FBL you need it set that way, NOT the "3 servos 120 degrees" way.

04-01-2012, 01:56 PM
I replaced the RX with a new one, solved all the problems I was having.
Also replaced the boom as it had a hairline crack in it that I couldn't see for a long time.

04-01-2012, 06:50 PM
I bet the crack was along the vertical edge, i.e. along the line where the two halves of the boom, top and bottom, are joined?

I've found that spreading a bit of CA along the surface and twisting the boom 'left' and 'right' to work the CA into the minute cracks seems to help stiffen it back up by quite a bit.

On the other hand, my boom, which has/had a few cracks in it was more stable and less likely to vibrate than another pilot's boom that was brand new in a recent comparison.

Not that such a repair would have saved you the trouble and expense of a new tail boom but instead more so that if one has a cracked tail boom, a bit of CA might be just the ticket to get it back into functional usage again.

04-02-2012, 11:03 AM
A boom with tiny cracks seems to lead to pushing the A or B gears off the shaft. I think the boom and shaft flexes and literally pushes the gear right off. (Usually, the A gear.)

BTW, had a good hit on Saturday and snapped the boom right in half. :) I'm losing too much altitude on the second half of my backflips.

04-02-2012, 04:25 PM
Hey Benvk,

I was checking my blade pitch today and guess what ! I've the same problem on my left servo !

Before I go taking the Heli all to bits tho I think I will try powering the RX before the TX and see what kind off difference it makes!

Just one question tho "why does the manual make such a big deal about powering the transmitter first" ? Is there probable damage that may occur from doing it in revers for extended periods ?

PS, I sent you a buddy request not so long ago..

04-02-2012, 04:57 PM
Also I purchased a slipper clutch from bob for my 120D02s and would really appreciate
some advice on removing the ball linkages to fit this contraption ! I've not yet fully dissembled the tail rotor and cant find ball link pliers small enough for the job!
My fingers are to big and i don't want to order more replacement parts because i botched it.
Any and all help would be great Thx.

04-02-2012, 06:42 PM
Also I purchased a slipper clutch from bob for my 120D02s and would really appreciate
some advice on removing the ball linkages to fit this contraption ! I've not yet fully dissembled the tail rotor and cant find ball link pliers small enough for the job!
My fingers are to big and i don't want to order more replacement parts because i botched it.
Any and all help would be great Thx.

I just grab the blade grip flat between the hub and ball link with a needle nose pliers and then use a fingernail/thumbnail to pop the link off just catching the edge of the link. Works great.

Then to put them back on I just line up the link and ball and gently squeeze with needle nose. This prevents pushing the links on too far.


04-12-2012, 01:40 AM
Hey all. New to the forums. I was searching this servo creep issue and found this thread. I wanted to share my results.

I had this exact same issue with my D02S. Holding it, or even slowly throttling up while it was sitting on the ground would result in the rear left servo creeping downward slowly until it was all the way down. I was pulling my hair out. Finally, after reading this thread, I looked and noticed that my RX was touching the front servo. All I did was unstick the RX and move it forward JUST enough to not be touching the servo. The servo creep issue is pretty much entirely gone after doing that.

04-12-2012, 03:48 AM
Good to hear, please send a blank cheque to Ben, 62 Devonshire Road, London, England. :lol:

04-12-2012, 12:52 PM
Good to hear, please send a blank cheque to Ben, 62 Devonshire Road, London, England. :lol:

And, sign it 'BenVK'. :tongue

04-13-2012, 12:23 AM
sorry i don't have any cheques. will a check do? :rotf

04-13-2012, 01:27 AM
sorry i don't have any cheques. will a check do? :rotf

Only if its the rain proof kind, you know, rubber? :lol: