Helicopter Rotor Direct Drive

[Boggy]

how about a pitch arm like the raptor mmcp uses? no need to modify the swash at all.

[Quadrotor]

I had a thought today. Instead of using a single rotor with 3 smaller props for control, why not have 4 rotors.
On standard quads they are limited to a prop size as they use motor speed to control lift. As i am using collective pitch for lift it will allow my quad to maneuver a lot faster.
Aswell as this using 4 larger rotors will allow for massive lifting ability, so could carry decent payloads.

Whats your opinion on this guys??

[Boggy]

Its already been done is my thought

World's First Full 3D Quadcopter Dominating - YouTube

[dillwhacker]

There was an interesting thread on here about that - someone pointed out that at zero pitch during 3D moves, you have zero rudder capability...

[sp4rky-m4rky]

There was an interesting thread on here about that - someone pointed out that at zero pitch during 3D moves, you have zero rudder capability...

Yea I never did get the answer. Although I know how it can be done I dont know how it is done.

Variable pitch, Variable drag, variable torque. Torque reaction induces yawing moment. Think about it at zero pitch though and how it would yaw whilst maintaining constant overall lift. Or picture the sweep from positive to negative pitch whilst yawing, for example during piro flips (which the stingray appears to be capable of).

[Quadrotor]

My understanding of a how a quad yaws, is to slow down the counter rotating props.
Theres probably more to it than this tho. Also may sound silly but can heli blades sustain lift at zero pitch??

[Quadrotor]

Thats a cool video. Some skills there. My goal isnt to produce a sporty aircraft but rather something that can perform tasks.

The reason i started looking at the heli rotors was due to there lifting ability.

I have now got a design sorted for a rotor bearing block. This will include a tachometer so i can monitor the rotor speed. 3 servos will control the collective pitch.

I will write custom firmware to keep the rotor speed and pitch in check.

[dillwhacker]

I guess near zero pitch there will still be some drag from the blades, so you could get some yaw from speeding / slowing diagonal pairs, like a normal FP quad does...

[sp4rky-m4rky]

So the stingray slows two sets of props down and speeds the other two to yaw? Erm but they are driven by one motor and driven together. And of course spinning blades at zero pitch still have drag and of course the drag increases with increased angle of attack but if all are at zero pitch there will be no yawing moment.

I guess near zero pitch there will still be some drag from the blades, so you could get some yaw from speeding / slowing diagonal pairs, like a normal FP quad does...

[dillwhacker]

Ooopps I may have slightly overlooked the fact that they are driven by a single motor...

[J3DI]

Like you say, the Stingray has 1 motor and all props run at the same speed. To change the torque of a particular rotor it requires a change in pitch as opposed to rpm.

Eg; Increase pitch of CW rotating props = increase CCW torque = CCW yaw. (Reduce pitch of CCW props at same time = even more CCW yaw!)


I was always troubled with what has been mentioned, where all props are at zero pitch. If you were to look at an individual rotor at 0 degrees, i think there will still be some torque reaction, but it will be at a minimum. Therefore if all 4 props = 0 degrees there will still be a small degree of yaw available, but not much. I don't think this is a normal situation or for very long anyway.

[sp4rky-m4rky]

My point is that, with all blades at zero pitch, yaw is balanced. To yaw there needs to be an unbalanced torque. An unbalanced torque from the increased pitch (positive or negative) from two props. Increased pitch changes the overall lift, the opposite set of blades would need the same amount of pitch in the opposite direction to restore the same overall lift. If not the model would gain or lose altitude during a yaw command.

The thought of a piro flip is more complex to describe but have a go at picturing that one.

Like you say, the Stingray has 1 motor and all props run at the same speed. To change the torque of a particular rotor it requires a change in pitch as opposed to rpm.

Eg; Increase pitch of CW rotating props = increase CCW torque = CCW yaw. (Reduce pitch of CCW props at same time = even more CCW yaw!)


I was always troubled with what has been mentioned, where all props are at zero pitch. If you were to look at an individual rotor at 0 degrees, i think there will still be some torque reaction, but it will be at a minimum. Therefore if all 4 props = 0 degrees there will still be a small degree of yaw available, but not much. I don't think this is a normal situation or for very long anyway.

[dillwhacker]

Isn't that the whole issue - at zero pitch (zero lift) the only thing you can do to maintain zero lift is put a positive pitch on one diagonal pair and an equal neg pitch on the other - which results in zero yaw as they both produce equal and opposite torque...

[J3DI]

It would be impossible to describe a piro flip, however, the Stingray is capable of the maneuver so the physics must be right!

[J3DI]

I see what you mean. If you demand zero lift you are only able to demand zero yaw.

If you want to yaw = Unbalanced pitch on prop pairs.

Unbalanced pitch on prop pairs = a collective pitch one way or another.


I guess with a piro flip, once you have initiated the yaw it will continue to yaw as you go through the zero pitch (lift) part of the maneuver briefly as you are in a balanced state with the prop pitch.