Winter is coming...XK K120 modified and... it flies .) - HeliFreak
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Old 11-27-2016, 01:29 PM   #1 (permalink)
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Join Date: Oct 2016
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Default Winter is coming...XK K120 modified and... it flies .)

Winter is coming. No light in the evening and very cold, so what better than modifying the helicopter...
I finally completed the mods I had in mind. A new canopy was also needed, still unpainted. Vacforming was taking a bit of time... never did it before. No way to fix the original one to the new battery position on top.
Well... it flies and arrow servos are very fast.
I used CFRP everywhere possible and replaced main mast with a carbon one. Still the weight is 5 grams more htan the original.
I have more ideas where to save weight but first of all I need to try it in open space to see how it flies at full power. Testing in the livingroom is not enouth, at least for my skills (no way to move to full throttle or 3G in closed spaces).
Hope you like the pics and any feedback and sugestions (including ideas for further mods and maybe a more powerful motor (or smaller pinions?) are utmost appreciated.

Max
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Old 11-28-2016, 02:41 AM   #2 (permalink)
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Max,
How those servos fit with the stock frame?
I'm interested in those servos, metal gears and seems to have good speed as well.
Did you try them in the stock frame first?
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Old 11-28-2016, 12:27 PM   #3 (permalink)
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Yes I did. And they barely fit. You have to make minor mods.
1 stock servo holder in the back is OK but stays 2mm higher thus you have to add a little spacer to the screw
2 you need to trim a bit the front holder that also stays 2mm higher and than interfere with the screw of the mast retaining washer
3 you need to cut a bit front servo housing on top for same reason...a bit weired but works just be careful to take away just a small circle. Tondonthat you need to replace the arrow servonshrink sleeve with kaprTon tape. Younalso need to remove the back closure of servo since it interfere with the back servo arm and push rod to the swashplate.
4 cut the servo fixation lugs so they do not interfere with the main gear
5..... And here it gets a bit tricky... My arrow servos are reverse so I had to open them and rewire motor and position sensor. But I think that if you order the ones with the right rotation direction then you can skip this painful point... Soldering the internal small wires is a pain...
6 you need to shorten by 2mm all the push rods by screwing them to the maximum and the servo arms in neutral should be a bit "down" then swashplare is levelled with no need to rework the push rods. It is not perfect symmetric when you go from positive to negative pitch but it is not too bad

Well... A bit of work but with this servos I crashed tons of times VERY HARD and they always work....
Ah... Of course you need to replace the connectors to fit the k120board but this is easy. Yost take care of correct wiring. I made a mistake and burned the receiver....

Consider I did it because I found 6 arrow used servos for 20euro in eBay and took them thinking of a plug and play situation.. Well it was not!!!

My opinion... If you like to spend time in building stuff do it. Otherwise just order replacements. Takes a second to replace and yes... They are a bit slower and screw up just looking at them but adapting the servos require lot of work and tuning. That is also why I then decided to build a custom frame that can host them more properly. Sorry but I have no picture of how it was looking before changing the frame.

If you decide to try let me know and I can send you pics of the modified parts that I still have.

Ciao
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Old 03-30-2017, 12:43 AM   #4 (permalink)
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Hi there,

Are you using the Futaba Radio or the one that comes with the kit?

Did you had to reverse servos in the radio?

Thanks for the info, I'm trying to use some walkera servos I have around but I need to reverse the channel in the tx and now it won't calibrate.

Thanks
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