RC India

Hello everyone,

I built this bicopter, it flies ok.  Needs more tuning but it's working.  I thought I must share it, so that it may help someone.

Bicopter can be made in two ways

1) Front of the craft is perpendicular to the line passing through the shafts of the motor
2) Front of the craft is passing through the shafts of both the motors - I will be discussing about this one

You need to use two servos in order to tilt the motors.  And to achieve this you will need 'mmix' and 'smix' codes i.e. motor mix and servo mix codes.

To make this type of bicopter you need to select 'Custom Tricopter' (selecting bicopter did not work for me), also it did  not work with betaflight, cleanflight, so I used iNav and it worked.

Apply this code in CLI tab (just copy paste):

#code starts here

mixer customtri

mmix reset

mmix 0 1.0 0.0 -1.0 0.0
mmix 1 1.0 0.0 1.0 0.0

smix reset

smix 0 0 0 100 0
smix 1 1 0 -100 0
smix 2 0 2 100 0
smix 3 1 2 100 0

save

# code finished (copy till here & paste it in CLI Tab)

later you need to set servo output on pin 7 and 8 of the FC. Pin 1 and 2 are connected to the ESC's and ofcourse servos to pin 7 & 8.

I hope it helps someone.

You can try 50 instead of 100 in smix code, go further till 100 and find out the best suitable value for your bi.

smix 0 0 0 50 0
smix 1 1 0 -50 0
smix 2 0 2 50 0
smix 3 1 2 50 0


Swapnil N.

 :hatsoff: to you sir. Heard that balancing chinook type bicopters is not that easy. Thanks for sharing. {:)}

Hey Swapnil! Please share a video, would be pleased to see. You must've already watched Tom Stanton making one ;D

Here's the video
https://youtu.be/28kv85bDE-0

interesting project. how's the controlling? is it responsive or needs efforts? I think bigger props can reduce agility and increase stability.

This was also done by someone on YouTube if I am not wrong.
I think it was Tom Stanton.

Yes Tom Staton has done it, I had asked him about the code and betaflight setting which he did not reveal.  It took me a lot of time to understand the 'mmix and smix' terms.  Still it was difficult for me to write proper mixing codes. With someones else's help I was able to make this bi, so I thought I must share the basics (like code etc) with everyone. 

Swapnil N.

Very nice swapnil Nimbalkar

thank you everyone!

Is this thing as stable as a quad?

It depends. A lot of tuning is required. Even controls are very difficult. I've tried building it (from scratch) and have terribly failed.

But if you were to build a stable system, which takes minimal inputs from the user, and fly steadily, then it will be better than a quad.
Considering, it uses two fewer motors(for thrust).

I'd love to build one, and I'm planning to ;D

I asked coz, if it is we could have twice the flight time and still have a super drone.

Yeah. Theoretically, yes (considering the servo sucks very low power). But stability is an issue.

You will have to spend quite a lot of time tuning it.

Anyways, I'll be making my own and will upload the whole arduino IDE code. I'll do it with my new stm32 ;D

there is a basic concept to explain this.

imagine the multirotors are your chair.

if the chair has 4 legs it's super stable, like quad.
if the chair has 3 legs, it is quite stable but not so much. like tri-copter.

if the chair has 2 legs, it's difficult to balance but can be stable at some point. like bi-copter.

It all depends on the feedback loop the whole system has. based on the feedback loop the sytem reacts.


Regards,
Karthik

I too am trying to build one. Have it almost working in betaflight 3.1... Just my roll smix has one servo reversed. When i use smix reverse n n r it reverses it but i lose 90% of travel. Can post dump and pics/vids tomorrow as i need to sleep now. I do have a question though. Is your yaw authority governed by the motors or the servos?Thanks for your post Swapnilnimbalkar. I am not ready to give up on betaflight it has to be possible. 

Hi. Sorry for being late.
1) My yaw authority is governed by servos.
2) You can reverse servo inside betaflight servo tab too. Make it -100%