Chinook Tandem Heli Build Thread

Aerobatic, DCP 30%, Ch5 mix 90%, gyro 35%


Flight with flybar weight added



4th flight


1st flight



Materials:
1) 2 x Trex 450 RotorHead CC and CW modification, $800 HKD
2) DIY Body Frame 1.5cm fiberglass (can use metal cutter) , $50
3) metal bearing mount x 3 pairs, $150 HKD
4) 5mm copper tube , as tandem torque shaft, $30 HKD
5) Miter gears x 2 pairs . spare parts from gas heli torque tube, $54 HKD
6) TH2 mixer ~$1200
7) Pitch gyro Align 500X (old version), Yaw: E-sky 704A HH gyro $230 HKD
8) 500T. 1900kv @15T
9) Towerpro 9g servo x 6 = $180 HKD, servo wire extension x 3
10) Fiberglass 325mm blade 2 pairs, $ 70 HKD
11) 45A Himodel Heli ESC $140, AR6100 6Ch receiver, Align 3A BEC , 3s 1800 lipo

Flight 1:Failed , due to bent hollow main shaft from Ground Resonance?? Vibration caused by too high headspeed and the 2 towers shake like crazy.
Flight 2:Successful hovering , but lots of hunting due to unwired GY401. Resolved using cheap E-sky 704A gyro on HH mode without gain wire connected.
Flight 3:
Successful level flight. Used 2 HH gyro. Need to stregthen frame for the torsional stiffness.
The driving shaft may need 4 bearing support rather than 3. Trex600N needs only 3 bearings. Maybe the shaft-->miter gear connection allows more vertical/ horizontal clearance.
Flight 4:
Vibration comes from torque shaft alignment and frame torsional deformity. Problem solved with additional frame support and realignment of torque shaft bearing mount.
Perfect hovering and forward flight. Very stable Headlock yaw and pitch control.
Flight 5:
Try adding the flybar metal weight (~1.8g). It makes the Tandem much more stable and real. I can off my fingers off the Tx for 10 seconds now.You may need to reduce the gyro gain then.
The front rotor vortex is rather interesting. I intentionally reduce the pitch gyro gain <40%>30cm in a sudden. First I though it is low voltage throttle cut. Then I remember it is what Joe mentioned. You must increase the throttle stick (as much as 2/5 throttle ) to regain altitude. This is real fun to see it happens!
I also observe another interesting phenomenon that does not happed in single rotor heli. When I do a fast piro, the whole bird seems obtunded after turning 180degree. I guess the front rotor turned into a position where the rear rotor was before. The turbulance will then counteract the coming rotor a bit. Anyone can confirm this?
Need to increase TH2 setting DCP gain , as 30% mixing still have Front Vortex Interference on slow FF. The remote Ch5 DCP gain works great as I dial it up to 90% in very windy condition >20km/hr.
Did some aerobatics today and fast FF is perfect.