Cyclic Control by Pulsed Torque

[Chiplight]

This has got to be one of the most interesting ideas I've seen in a while.
http://www.rotaryforum.com/forum/attachment.php?attachmentid=11047

The R/C helicopter in the attached photos has no swashplate and no control rods at all. Also, no servos, yet it has full control of roll, pitch, yaw and collective thrust- cyclic control is achieved by pulsed torque to the main electric motor. The pulse is timed correctly using an optical sensor and sensor plate that rotates with the main rotor. Yaw control is simpler, with just changes to the tail motor speed.

I'll admit that I had to look at this thing for a long time before I comprehended it.
The motor is pulsed on and off in different parts of the rotor's cycle. This causes the fixed pitch rotor to create more thrust during that portion of the cycle that the motor is driving it. Control inputs take effect 90 degrees later in the cycle, just like with ordinary swashplate control.

Collective thrust is controlled by varying the duty cycle of the pulses to the motor.

There are two gyros: one is yaw-axis for tail, and the other a "free gyro" which is two-axis for cyclic.
A video in japanese is available on this page http://www.nanorc.com/revolutor.php
more pics here
http://www.vassfamily.net/heli/tech.html

[Dave_Jackson]

Chiplight,

I am not quite certain how the cyclic will operate, so for the fun of a discussion, here is a modification to your thoughts.
__________________________

The governors only exist to provide stability.

The main rotor is extremely rigid, in that it does not teeter, flap or lead/lag. There is a common connector between the two blades that causes them to change their pitch in unison. When the pitch of one blade is increased (say from +4º to +6º), the pitch of the other blade will decrease (from +4º to +2º). An arm extends down from this common pitch connector. The motor causes the rotor to turn by applying force to the bottom of this arm.

When the motor is not driving, this arm will be hanging strait down and both the blades will have +4º of pitch. When the motor is driving it will apply torque to the arm and this will cause one blade to go to +6º and the other blade to go to +2º.

Lift is achieved by pulsing the motor at equal increments around the full azimuth of the rotor disk.
Increased lift (collective) is achieved by increasing the quantity or the duration of the pulses at equal increments around the full azimuth of the rotor disk. This gives a faster rotational speed.
Cyclic is achieved by increasing the quantity or the duration of the pulses near one azimuth and decreasing the number or the duration of the pulses at 180º from this azimuth.

Dave

[rotorque]

This can play with your head,

I assume that the max pitch is a fixed angle. The motor does very small pulses per revolution at the appropriate azimuth thereby deflecting the blades equal and opposite to the max pitch. In a 'steady' hover the poor little helicopter will be copping four spurts from the engine which is then transfered through the fuselage..... On a full scale helicopter, the pax would be feeling an extremely uncomfortable 4 per bounce. It is only the fact that RC's have a relatively higher RPM that it may be acceptable.

Dave, the blade system wouldn't need to be a 'rigid' head as you described. The way I have come to understand it in my head....(read that how you will)..... the head would be a teetering head, similar I guess to an old 47.

Cheers

[Capn Notarious]

I'm waiting for Lu's response.

This will doubtless get his grey cells working.
If you read this LZ kind regards.

[NickLappos]

Just try to imagine what the ride would feel like!

What this does illustrate is a bit of what I was describing in that Dave jackson thread about rearranging all those big mechanical parts to achieve "symmetry" and "stability" - modern electronics have the power to stablize helos so that screwy mechanical systems are no longer the solution to stability issues.

[Hilico]

What would the TR be doing during these pulses? It sounds as though it would be required to change thrust precisely and instantaneously.

[Chiplight]

Dave,

your explanation makes sense. I accept the modifiction to my theory of operation. I also tend to agree that the rotor is rigid in the sense that it is not free to teeter. The link attached to the shaft does not look like it would permit teetering motion, only "feathering". The whole helicopter must tilt in the desired direction but still there is a 90 degree between input and tilt response, (or is it 72 deg?).

When the rotor is under torque, one blade is always making more thrust than the other, whether the heli is tilting or not, assuming the blades are mounted with equal pitch.
This does not cause a wobble in level flight just as a single-bladed helicopter does not wobble from having all the lift on one side as long as the weights are balanced. Counter intuitive as that seems, its true. (That deserves a seperate discussion.)

As for the tail rotor, I think that it merely needs to produce a steady thrust, not instantaneous bursts of thrust.
The torque to the main rotor is in the form of rapid pulses. These pulses likely occur on the order of hundreds per second, so rapidly that they are integrated into a continous torque at the tail.


The only thing that the electronics can't solve on this helicopter is the problem of engine failure leading to loss of cyclic control- not to mention loss of rotor speed.
On second thought-if the fixed pitch is set at the best autorotation pitch then the loss of drive will set the rotor into automatic autorotation!

.

[Lu Zuckerman]

To: Capn Notarious

I'm waiting for Lu's response.



It would seem that on the model helicopter there is a great deal of flexibility in the drive line and with a low level of inertia in the dynamic system the model helicopter can tolerate the acceleration and deceleration of the blades. However on a full size helicopter the inertia of the blades and rotorhead is quite large. The constant acceleration and deceleration of the main rotor would manifest itself in torsional windup of the rotor mast and further manifest itself in overstressing the internal workings of the transmission. These same loads would also be reflected in the attachment of the transmission to the fuselage requiring a special vibration damping system such as elastomeric couplings.

The tail rotor driveline would be subjected to the same torsional windup but at a higher frequency resulting in overstress of the shaft, couplings and the tail rotor and tail rotor gearbox.


:E :E

[Chiplight]

Lu,

I imagine that the torque pulses to the shaft are so rapid as to look like a steady torque, similar to an anti-lock brake system.
The avg value changes during a part of each cycle if a stick input is made, but even then, there is not a large spike being delivered because of the PWM type modulation.
In a hover, rather than 4 large pulses, 1 at each quadrant, you could apply several hundred shorter pulses averaged around the circle to achieve the same torque.

[delta3]

Electronics can do a lot, but there is quite a big hurdle to overcome in the fact that dynamics of a model and of a full scale model are quite different.

Things that work on a scaled model may be very difficult to achieve, because 'the mix' required to achieve it drastically changes when we go to different scales : length goes linear, volume cubic etc. So finding a control on a larger/full scale model may be quite more difficult.

Delta3

[Thomas coupling]

Can you imagine going out for a beer with these guys:{

[Dave_Jackson]

How about using two optical sensors, two electric motors, and a closed-loop controller; to electrically inter-phase a pair of main rotors. :rolleyes:

Nick gets "modern electronics", Dave gets "lateral symmetry", Rotorland gets a new helicopter and everybody gets TC to buy the beer. http://www.unicopter.com/drinking_smile.gif

[Chiplight]

Something along these lines, Dave?

http://www.rcgroups.com/forums/attachment.php?attachmentid=168760

This micro-heli is using a commutator to control a motor, which, in turn controls a flybar. In some models, the motor or, an actuator, controls the blade pitch directly.

[Dave_Jackson]

Chiplight,

That sure is a small motor.

The wild idea for counterrotating main rotors was along the lines of the closed-loop feedback control method that is used with servomotors in CNC machines. The azimuths of the rotors could be read and then the phasing of the rotors could be independently changed to assure that the rotors never got out of synchronization with each other. Just a crazy idea.

I vaguely recall some university that produced a single-blade helicopter for use as a UAV. They mentioned that the vibration was acceptable for camera surveillance, but as Nick mentioned, they said it would not scale up to a large craft. Your thoughts about autorotation and the single rotor might be compatible. This is because placing one blade at a low pitch for autorotation would not set an opposing blade (on a 2-blade rotor) to a high pitch.

Here is a web site for you;
A Stop-Rotor Hybrid Micro Air Vehicle (http://www.nrl.navy.mil/techtransfer/exhibits/pdfs/Info%20Sheet%20pdfs/UAV%20Info%20Sheets/Samara.pdf)

Dave

Edited to improve grammer ~ hopefully.

[Chiplight]

Wow, Dave, that is interesting.

Great link. :D

[slowrotor]

Yes that is interesting. And proves that more rotorcraft configurations are lurking in the future.
If both of the single blades were mass balanced, it just might work in full scale. But I think the rotor and main shaft would need to be strong (heavy) to absorb the onesided lift of each blade.

[Chiplight]

Another stopped rotor concept:
http://www.seeop.com/spinwing.htm

[Dave_Jackson]

Nuts! The conversion animation is missing.

It would have been interesting to see it takeoff in 'reverse', then fly off in 'forward'. :rolleyes:

[Chiplight]

Are we having fun yet?

How about the "entomopter"; The blade pairs tilt , or flap, intstead of rotating. Some serious research is going into this.

http://gtresearchnews.gatech.edu/reshor/rh-ss03/sp-main6_b.jpg

One question concerning the stop-rotor design using counter rotating single-blade rotors: Twice per rev the blades are on the same side. Iwould think that they would need to be individually counter balanced, leading to a solution thats twice as heavy as a normal rotor.

[Head Turner]

Some time ago someone invented a mechanic system for collective and cyclical pitch changes. Has anyone a clue as to what this item was called? As far as I can remember it's a rather simplistic system using a ball race and rods.

I'm going out for a beer!

[Dave_Jackson]

Here is a group of interesting German VTOL concepts (http://www.vstol.org/GermanVSTOLRotorcraft.pdf), which might be new to us Anglophones.