It turns out that in terms of the rotor gear that many of the parts for the K120 are interchangable with the K110 (for example my k110 had a crash and since the gear, which is held on by friction (no screws at all, just friction alone and the circular rotor head made into a semicircle so the gear wouldn't spin when power was put to it.

However I've discovered that since I have plenty of XK 120 spares including the main gear I put the main shaft from a k120 into the K110, fitted a gear for the K120 and it was fine. I fitted the metal rotor head, swash and everything else which is also apparently interchangeable and this is where I ran into issues. In 6g mode the servos would react fine, however on take-off the heli kept flying to the right side. Since I was indoors I wasn't trying to fly high and no damage was done to the heli. I recalibrated the gyro and tried again. It kept leaning to the right and would only fly if I gave full left ailereon, there were no servo issues and all of them worked fine at changing blade pitch, it was like the gyro couldn't fight it.

I changed back to plastic (which is about 15 minutes work and hovered using the same gyro settings, the helicopter flew fine.

Any ideas on why it would do that? I'm completely stumped.

Edit:
I separated the metal swashplate from the heli and it seems to be flying fine now. Although it seems to want to go forward no matter what I tell it and I can't get it into a stable 6g hover, though this was also a problem with the no fisheye, plastic swash.

Are the ball joints nice and free moving on the servo to swash links ? If they are even a little bit tight it will cause it to be virtually unflyable ,I was thinking you had possibly used the k110 servo rods and the balls on the k120 swash might be slightly bigger causing them to bind ?

Originally Posted by dadio

Are the ball joints nice and free moving on the servo to swash links ? If they are even a little bit tight it will cause it to be virtually unflyable ,I was thinking you had possibly used the k110 servo rods and the balls on the k120 swash might be slightly bigger causing them to bind ?

I've actually removed and attached the fisheye swash from the metal head and put it on the 110. The heli keeps flying forward and my backward pitch is almost maxxed out though I'm not sure if that's the swash or the bigger batteries making it front heavy. I'm having trouble getting it to hover though it's winter and very windy so I can't really go outside and trim it and I honestly think it's a trimming issue as I can get it to hover in a 1.5-2' space, but only with stick input though I had the same issue with the 110 swash (but had less manoeuvrable because no fisheye and an overall cheaper bearing setup

I would like to mention that anyone who owns an 110 they should buy 120 main shafts and gears. Totally interchangeable and the main gear actually screws on (I lost my first main gear in a hard landing because I didn't know that they were just pushed on and held in place by friction) since the motor on the 120 is more powerful the gears are tougher and don't seem to strip like the girl you hired to the stag party upon the slightest contact with something
I saw the heli lean to the right and had to reset the gyro so it may be gyro related, though I'm happy enough with plastic grips, it was mostly the swash plate I wanted. I'll see if I can get some graphite lubricant and make the connections a little more slippery as when I do get a hover it seems to suffer from some sort of toilet bowl effect, which I think is due to the connections that aren't overtight being just a little too tight and thus are slower than normal to respond to input.

Anyway I have a BNF 120 on DHL mail (just got picked up in china) so it should be here in a couple of weeks. I had one but it caused the servos to cook themselves due to a faulty distribution board, the site I bought it off offered me replacment servos and a distribution board but since; don't ask me why they they thought this was wise, it seems on the 120 the designers haven't yet discovered screws yes that's right the servo distribution board is hot glued to the frame but the kicker is the fact that the servos have no screws holding them together. What holds them together is the 'decorative' stickers on the sides of the servos.
Anyway we agreed that instead of painstakingly gluing the thing together I could get a new BNF half price, which I agreed to since I have a bunch of spares.

The linkage arms on the 120 blade grips are longer than those on the 110 and have a different response ratio compared to the 110 setup and hence why the 6g setup gets confused. It thinks it has applied a certain amount of correction, actual value is about 12% less.......

It should ? With a 6g calibration flight sort itself out. Maybe. You need to add more pitch, aileron and elevator setting as well.

120 - get a set of Emax servos and change the plug ends, no more problems, super durable
The servos on these are plagued with issues, the motors are to small is the underlying problem and the gear sets are weak. Get rid of them is the best solution. Not uncommon for small servos to just have a shrinkwrap band to hold them together (blade 200 srx for example) or similar and no screws.

Just fitted the 120 swash into a 110, all good after a 3G calibration followed by the 6g hover setting. Important to get the mechanical trim good in 3G first then the 6g will be very close. When trimmed right in 3G you can switch back and forth 3G - 6g without any darting away.