RX120-2S - Printed size 120 helicopter with power from 2S battery, prefinal assembly. - RC Groups
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Mar 08, 2018, 08:51 AM
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RX120-2S - Printed size 120 helicopter with power from 2S battery, prefinal assembly.

I want to thank Mike Jennings (MikeHRC) for the translation!!!

Today there will be a small continuation of the previous article https://www.rcgroups.com/forums/show...y#post39299621 about the printed size 120 helicopter powered by a 2S battery, so for starters I recommend getting to know it.

As I already wrote, the head of the problem in the trial version was the unstable operation of the tail. The root of this problem was in the flight controller, and it was not possible to solve it for me, not the flight controller.

So I decided to use the flight controller, and regulators, from the relatively new Align 150X helicopter. All this together is called the 150GRS Flybarless System Set and is a combination of regulators, flight controller and receiver bundled together.

However, I had to disconnect this kit a bit to install it on a helicopter. I decoupled the regulators and attached them from the bottom of the frame, and the flight controller with the receiver remained at their usual place, from above.

The flight controller and speed controller are very pleased with their compact size and light weight.
Well, the most important plus of 150GRS is the ability to configure it !!! To do this, there is a mobile application, when installed on a mobile device, you can connect to the flight controller via bluetooth, and configure a huge number of flight parameters and the operation of the flyback system, including all parameters that are responsible for tail operation.
Thanks to this opportunity, I could easily adjust the tail and the helicopter flew! I reduced the parameter of the gain for the tail motor and the tail began to behave stably. Also adjusted the rest of the parameters and achieved a clear and fast response of the tail to the stick.

However, as they say, everything can not be good, and there were unexpected surprises.
The flight controller 150GRS is designed for a certain resolution of helicopter mechanics. That is, the ratio of the translational motion transmitted by the servo drives to the final blade deflection angle. And to my chagrin this gear ratio did not coincide with the gear ratio of the mechanics of the V977 / K110 / K120 helicopter, which I used in my helicopter, it turned out to be too small.
In particular, the differences were in the length of the pivot arms, in the length of the servo arms themselves and in the maximum deflection angle of the servo drives. 150GRS operates with a much smaller servo range than the flight controllers from the V977 / K110 / K120, so the stroke is much smaller. And accordingly, the angle of deflection of the blades will be smaller. Therefore, during the first flight, I was glad that the tail earned normally, but was disappointed that the helicopter was very sluggish, because of inadequate mechanics. The easiest option was to use the original mechanics of the Align 150X helicopter, but I went the other way.

I decided to change the existing mechanics of the helicopter so that its gear ratio would be higher. To do this, I had to replace the trunnions. Instead of metal trunnions from the V977 / K110 / K120 helicopter, I installed metal DFC trunnions from the V931 / K123 / K124 helicopter. These trunnions have a shorter lever, and accordingly a higher gear ratio.
for their installation I had to finish the hub a little. I cut off the guides for the links, and gently strewed, in a lathe way, what was left of them. The hub turned out to be nice and neat, as if it were.

Changes in mechanics had a very positive effect on the flight. The helicopter revived, became cheerful, as expected! In addition to changes in mechanics, I had to reverse the elevator servo, in order for it to correctly process signals from the flight controller. In the final version, I plan to get rid of the reversed servo, to simplify the assembly. For this, the main engine and the elevator servo will have to be swapped. On the flight, this will not be reflected in any way, and assembling the helicopter will be easier.

I have already adjusted the positions of the engine and elevator servo in the 3D model of the frame, it remains only to print it and collect the final version!

All other components of the helicopter have not changed, so I will not tell you about them.

Last edited by remlen; Mar 08, 2018 at 09:17 AM.
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