Hello, I’m new here. I’m trying to build a Tiltrotor with two modes which are conventional fixed-wing and Tandem Bicopter. (the photo can give you a better understanding finished product which I’m upgrading right now) According to my study, it seems I need to rotate the x-axis and y-axis in Tandem Bicopter mode for 90 degrees, but I have no idea how to do this. Secondly, for this unique aircraft, I need to adjust the RPM of the back motor by an f(t) function ( red line in the table; the table shows only the process of fixed-wing mode transit into Bicopter) during the transition.
I really need you guys to tell me how to do these, adjust codes on which file, etc.
Hi,
I doubt your concept is going to work. There are two types of bicopters (well three, but the third does not work for a tandem config).
One is balancing the CG above the motors/props, like a stick on your finger, the other has the CG hanging below the props. Both require a careful setup of CG position, body length etc. Even if you could get away with the short distance between props and CG on your VTOL, the aerodynamic drag of the wings will mess up the roll balancing. The fuselage needs to swing freely below the props, but the wings will dampen that movement.
The second concern is, that you will need a mechanism that allows both motors to move around two axis. This mechanism needs to be free of backlash and stable enough to handle the thrust and gyroscopic forces of the props.
The third hurdle is that you want to use the rear motor during forward flight. This means, as you are showing in the diagramm, you have to reverse the motor direction during transition. If this is going to work is questionable, but the bigger problem is, props have a rotation direction. The rear prop will either be rotating in the wrong direction during hover flight, creating more noise than thrust, or it will do so during forward flight. The only option here, would be to fly forward with the front motor only, shutting down the rear motor. This would also mean you could leave the rear motor in hover position, saving one complicated 2D mechanism.
I am just stating the problems I see with your project. I hope you work it out and prove me wrong!
Hi, wow thank you for your high quality reply with in minutes!
Part1: I figure out most problems can be fixed by lower and lengthen the Beam( which connected the front and rear rotating mechanisms), and the the CG is still hanging below the props, I like to know do you argree with this solution or not.
Part2: Well, only real test flight can prove did I design and build all 4 rotating mechanisms good enough. I’ll let you know the result.
Part3: I like to make sure are you saying that the low efficiency of roataing the props opsit as it was designed to be(see photo)? If yes, you are right, and there’s no easy design can fix this. I’ll definitely test your solution, and let’s see which is the best solution. Let me know if you have a better idea.
By the way solution for Part3 is Swashplate. And the motor direction problem can be solved by Relay, but there should be a better way.
We still need to get the software working, in order to test all of these and improve this aircraft!!
Again, thanks for your high-quality reply!
A prop blade has a profile optimized to move air in one direction. It does not matter if you change the prop pitch to negative values or the rotation direction, the prop blade profile will work the wrong way around. There are some 3d props with flat blades for 3d quadcopters, but they are only available in some sizes and their efficiency sucks, too. Full size aircraft only use negative pitch to brake after landing, where efficiency and absolute thrust do not matter.
I do not understand the reference to a relay. Do you want to use a relay to reverse motor direction?
Relay: yes I saying use relay to reverse motor direction. Besides, RC cars can reverse motor direction without a relay. Does that mean Pixhawk can reverse motor direction without a relay?
I don’t know did you see my first reply or not. There seems to be a bug. Therefore I ask again here: “Part1: I figure out most problems can be fixed by lower and lengthen the Beam( which connected the front and rear rotating mechanisms), and the CG is still hanging below the props, I like to know do you agree with this solution or not.”
Relay: yes I saying use relay to reverse motor direction. Besides, RC cars can reverse motor direction without a relay. Does that mean Pixhawk can reverse motor direction without a relay?
I don’t know did you see my first reply or not. There seems to be a bug. Therefore I ask again here: “Part1: I figure out most problems can be fixed by lower and lengthen the Beam( which connected the front and rear rotating mechanisms), and the CG is still hanging below the props, I like to know do you agree with this solution or not.”
I think being able to reverse the motor is dependent on the ESC used. BLHeli and other types of ESCs allow for bidirectional thrust.
I haven’t used this feature myself but I imagine the flight controller needs to know which type of control signals the ESC expects to receive.
I believe some ESCs use a serial protocol rather than normal pulses though bidirectional ESCs should work with normal pulses as well.
Here’s one video I found about setting the direction in a BLHeli ESC.
You can not raise the motors to far, because that will cause issues with the thrust line in forward flight. The original motor mount of the Mini Skyhunter is positioned and angled to provide a neutral reaction to motor thrust. That means the thrust vector line should be aiming at the required CG position.
If you move the motors higher, your VTOL will nosedive during forward flight and even more so during transition, when there is no airflow over the control surfaces.
