Bi-copter racer

[Piotr Szalczynski]

I tried to lower the Derivative and while the servos seemed to make less overall buzz nad small shaking it affected the flight performance of the copter very negatively. Again he started to wobble when rapid change of flight. I returned to old values.

What kind of servo are you using ?

The thing about their speed I mentioned in one post and I am well aware of it. Previously I used the Futaba with medium performance and at low voltage so thjey did run at 0.13s / 60 deg. Now I use Hi voltage servos which are nearly 2.5 times faster. I plan to use 5 times faster ones in bigger version.

For the small copter I am using the effect of different flow condtidions over the propeller disc that you mentioned is much smaller than for 5-6 inch one.
-The radius of propeller is much smaller which I presonaly belive has less affect the secondary air flow conditions (would need some CFD investigation) .

-The props in my copter spins much faster therefore the relative change in the speed triangles and angle of attack between advancing and retracting blade is not so significant.

– I also use prop guards which could decrease this effect even more.
As you can see on the video I posted before I don to experience any more shake/wobble when flying backwards than forward if any. When I fly slow he can be almost perfectly stable sometimes even the servos almost does not shake at all. Soon I will use different FC with 7.4V feed to servos so I would use their full potential since now I am using 80% of their max speed at 5V

[Kevin_Erik]

TURNIGY TGY-306G-HV
https://hobbyking.com/en_us/turnigytm-tgy-306g-hv-ultra-fast-high-torque-ds-mg-hv-alloy-case-3-7kg-0-05sec-21g.html

[Piotr Szalczynski]

You use it for 5 inch ? I use same performance servo (3.7 kg / cm ) for 2.5 inch. I think I would try to go 0.02s / 60 Deg 12kg/cm Align for 5-6 inch one. Now I am going to build 17 inch and will use 50 kg / cm servo with 0.07 s / 60 deg

[Kevin_Erik]

Yeah I use it for 5-6″…. dont really see a point in spending more money then this. Diminishing returns and all that.

[Piotr Szalczynski]

I just wonder about the speed. The 3.7kg / cm is quite a weak servo and therfore the speed of 0.05s/60 deg under no load might be quite different when servo tries to rapidly change the position of 6 inch propeller disk with relatively high giroscopic momentum. I saw a huge difference when changed from 1.5 kg/ cm servo into 3.7 kg/cm.

[Kevin_Erik]

Thus far it’s flown fine for me. Keep in mind that my Bicopter is 450 grams with Lipo.

[Kevin_Erik]

@Piotr Szalczynski Forgot to ask you how are you powering the FC and Servo?

[Piotr Szalczynski]

Depends on copter. Nowdays I am using the matek 405 wing FC it has internal BEC so he takes power from battery and feeds servos with 7.2V (selectable). In the firdt small copters I was using the 5V from PDB so the servo performance was limited.

[Kevin_Erik]

Does the 405 wing work with 2S ?

[Piotr Szalczynski]

I never tried. Nominal voltage is meant for 3S-6S range. It boots up and seems to work but I have no setup light enough to fly with it using 2S and verify if it wont go down as soon as the voltage will drop cause of motors burden.

[Bruces]

What battery does this motor match? Lipo 3s battery?

[Author]

Posts