Luobo V2 AG - RC Groups
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Sep 27, 2017, 05:12 AM
bg1
bg1
Registered User
Question

Luobo V2 AG


I could use some technical help and I am hoping one of you guys here can assist.
I dont post much but just lurk and read.
I have bought a Luobo V2 from banggood. Its my first real AG.
It comes with a DC head which can be configured two different ways.
On one the servos are at 90 degrees to the mast .
The other option the servos are both at the rear of the mast and use a mix. coming from fixed wing I would say this was like an elevon type mix.
to tilt the rotor disk up at the front, both servos need to move down. Hope this is clear enough.
I have read the Gyrocopter Arodynamics therad. Its very good and helps with the understanding of how these work, well the parts I could understand.
My question is, if i use the 90 degree config, the servo attached to the side of the mast will attempt to tilt the rotor disk, in a left-right plane, not front-back.
Will this control input affect pitch or roll?
My gut says it will affect roll but the principles in the Aerodynamics thread say it will affect the pitch.

Many thanks in advance

Brian
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Sep 27, 2017, 04:49 PM
Registered User
Will this control input affect pitch or roll?
Roll.
Sep 27, 2017, 04:50 PM
I'm not as bad as they say.
Quote:
Originally Posted by bg1
I could use some technical help and I am hoping one of you guys here can assist.
I dont post much but just lurk and read.
I have bought a Luobo V2 from banggood. Its my first real AG.
It comes with a DC head which can be configured two different ways.
On one the servos are at 90 degrees to the mast .
The other option the servos are both at the rear of the mast and use a mix. coming from fixed wing I would say this was like an elevon type mix.
to tilt the rotor disk up at the front, both servos need to move down. Hope this is clear enough.
I have read the Gyrocopter Arodynamics therad. Its very good and helps with the understanding of how these work, well the parts I could understand.
My question is, if i use the 90 degree config, the servo attached to the side of the mast will attempt to tilt the rotor disk, in a left-right plane, not front-back.
Will this control input affect pitch or roll?
My gut says it will affect roll but the principles in the Aerodynamics thread say it will affect the pitch.

Many thanks in advance

Brian
A servo that tilts the mast to the side will affect the roll.
Latest blog entry: AIrcraft I've built.
Sep 27, 2017, 06:59 PM
bg1
bg1
Registered User
Many thanks

I must be over thinking things.
Oct 02, 2017, 04:28 AM
Registered User
TrueBuld's Avatar
Quote:
Originally Posted by bg1
Many thanks

I must be over thinking things.
Being new to this stuff and after reading the brain hurting but very informative aerodynamic thread by mnowell129, I can understand that question comes from the 90 degree delayed action.

So an explanation of how the two servo, two control rod fixed blade (elevons) system works; because I also envision that as the head is tilted (roll command) the leading rotor blade will pitch up causing the gyro to roll and pitch up at the same time?
Oct 02, 2017, 08:17 AM
I'm not as bad as they say.
Quote:
Originally Posted by TrueBuld
Being new to this stuff and after reading the brain hurting but very informative aerodynamic thread by mnowell129, I can understand that question comes from the 90 degree delayed action.

So an explanation of how the two servo, two control rod fixed blade (elevons) system works; because I also envision that as the head is tilted (roll command) the leading rotor blade will pitch up causing the gyro to roll and pitch up at the same time?
The rotor follows the mast tilt.
You can either have a pitch servo and roll servo at 90 degrees, so that one can provide roll, the other pitch.
Alternately you can put two at +/- 45 degrees from longitudonal and do mixing. Many do this to provide extra power on pitch.
It you use the +/- 45 arrangement you must do mixing so that for roll, the servos move opposite to make only roll in the mast. For pitch the servos move together to provide only pitch to the mast.
The aerodynamics of the pitch and roll of the mast are described in the aerodynamics thread.
Latest blog entry: AIrcraft I've built.
Oct 02, 2017, 10:12 AM
bg1
bg1
Registered User
Quote:
Originally Posted by TrueBuld
Being new to this stuff and after reading the brain hurting but very informative aerodynamic thread by mnowell129, I can understand that question comes from the 90 degree delayed action.
This is the problem I have been trying to understand. Following the principles on the Aerodynamics thread it seems that any action to tilt the rotor disk to the left will by the 90 degree action affect the pitch. I am sure I am missing something but I dont know what it is.
Oct 02, 2017, 12:16 PM
Registered User
Brian,
You said you are coming from fixed wing and understand the 2 servos working together as similar to elevons. You are correct. In an elevon mix, the 2 servos move together to act as elevator, or pitch control, and they also move against each other to provide aileron, or roll control.

Although there is more going on with a gyro's aerodynamics, the practical effect on the model is the same. The tilting of the rotor front back is like elevator and the tilting of the rotor left right is like aileron.

Having one servo do pitch and one servo do roll is fine, but the pitch servo must be strong. The use of 2 servos in the elevon mix configuration lets the 2 servos share the work load. This is an advantage because the servos don't have to be as strong.

I hope this helps.

Cheers!
Russ
Oct 02, 2017, 12:23 PM
bg1
bg1
Registered User
Rus1 . Thanks for that . I understand the mechanics of the servo operation.

What I am struggling to comprehend is the 90 degree delay which is explained so well in the aerodynamics thread.
If the cyclic action is delayed by 90 degrees then tilting the rotor to the side should make the AG alter pitch.
Something is not coming together for me.
I have most likely misunderstood something but I would like to get to the bottom of this.
Oct 02, 2017, 02:56 PM
Registered User
The asymmetric lift in forward flight is acting directly on the rotor blades. As explained in the aerodynamics thread this makes the rotor disk pitch up (and not roll) - and the rotor shaft gets tilted backwards as the whole autogyro is forced to rotate upwards around its CG. The asymmetric lift results in a torque, forcing the rotor mast to tilt backwards.

Now take this the other way round and use a servo to force the rotor shaft to tilt backwards. As before the rotor disk has to pitch up. The torque of the servo is acting direcly on the rotor shaft.

Apply this to the roll axis: The torque of the servo is acting direcly on the rotor shaft (this time to the right or to the left) and the rotor disk will follow this "roll" command.
Oct 03, 2017, 04:44 AM
bg1
bg1
Registered User
Thanks for the explanations. I finally managed to get it.

The steering the gyrocopter part of the aerodynamics thread has the answer.

The thread is explaining the forces created by the blades!! I was getting the disk and the blades confused.


My head is hurting but I think I am getting there.

Brian
Last edited by bg1; Oct 03, 2017 at 12:22 PM.
Oct 03, 2017, 04:19 PM
Registered User
TrueBuld's Avatar
Quote:
Originally Posted by mnowell129
The rotor follows the mast tilt.
You can either have a pitch servo and roll servo at 90 degrees, so that one can provide roll, the other pitch.
Alternately you can put two at +/- 45 degrees from longitudonal and do mixing. Many do this to provide extra power on pitch.
It you use the +/- 45 arrangement you must do mixing so that for roll, the servos move opposite to make only roll in the mast. For pitch the servos move together to provide only pitch to the mast.
The aerodynamics of the pitch and roll of the mast are described in the aerodynamics thread.
That information about the +/- 45 degrees is interesting as it is close to how the GyrOne seems to work.
Looking at the pitch and roll servo location ball joints they are (set at the front) and at an angle of +/- 40 degrees at the point of attachment with the actual ball centers closer to +/- 35 degrees relative to the pitch axes.
So the GyrOne uses as you state mixing to reduce the load on the servos.

The blade carrier is allowed to float up/down approximately +/- 8 degrees.

note:- measurements are eyeball using a small protractor.
Oct 04, 2017, 07:39 AM
I'm not as bad as they say.
Quote:
Originally Posted by bg1
Rus1 . Thanks for that . I understand the mechanics of the servo operation.

What I am struggling to comprehend is the 90 degree delay which is explained so well in the aerodynamics thread.
If the cyclic action is delayed by 90 degrees then tilting the rotor to the side should make the AG alter pitch.
Something is not coming together for me.
I have most likely misunderstood something but I would like to get to the bottom of this.
Tilting the shaft doesn't apply any force to the rotor or blades, that's part of what the flapping hinge does. With a flapping hinge (or a teetering hinge) there is no way the shaft tilt can do much to force the rotor anywhere.
What tilting the shaft does do is twist the blades, changing their pitch. So when you tilt the shaft to the right, the blade that is in front pitches up (CCW rotation assumed). This pitch up makes the blade have some extra positive lift, that 90 degrees later causes the blade to rise up on the left side of the model. Now the blade is tugging on the shaft with more upward force (and the one on the right is pulling down) and the model rolls to the right.
The rotor is not a solid thing, so it can't be treated like a gyroscope or bicycle wheel, so you don't steer it with mechanical precession like a gyroscope. This is a very common misunderstanding.
Instead you steer it by making the blades change pitch around the circle (i.e. cyclicly) and the blades will rise or fall and make the rotor plane tilt in the direction you want to go.
You just have to allow for the fact that the blade can't move immediately but takes about 90 of rotation to rise or fall. Hence when you tilt the shaft left or right you change the pitch of the blades when they are over the nose and tail (and not at all when they are left and right), and they rise and fall 90 later making the model roll.
Anyone who tells you that the shaft tilt is just forcing the rotor to move by mechanical force and precession, just doesn't understand the physics of what is going on.
Last edited by mnowell129; Oct 04, 2017 at 11:07 AM. Reason: typo
Oct 04, 2017, 12:04 PM
bg1
bg1
Registered User
Many thanks mnowell129

I am getting the idea. Its taken a bit of arm waving and hand twisting and my wife has been looking at me like I am crazy.

The part I was missing is tilting the shaft to the right affects the blade pitch fore and aft. Then 90 degrees later the effect is felt.

Its rather neat really, elegant even. It all just works but the mechanics behind the scenes are difficult to grasp.

Brian


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