Is this helicopter robot idea new?

I bought a small helicopter in Tokyo made by Keyence in 1995 that used this exact technique

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That helicopter uses two motors, not one. It has a tail rotor that stops the two large fixed blades from staying still and the body of the helicopter spinning.

Awesome! It would have taken me who knows how long to run across that model just by searching around for RC helicopter info. I'm a little unclear on just how the linkage works to pitch the rotors, but I can guess based on the pictures. If it works the way I think, it looks much more robust than the idea I posted.

I'm thinking that the small arms underneath the rotor hub are = such that one can freely rotate around the rotor spine while the other one is fixed. As the arms twist in opposite directions the rigidly attached arm pitches the rotors. Thus, the hub assembly is essentially symmetric in all respects except for pitch response. Is that right?

I'm a bit disappointed that this model requires physical gyroscopes for stability. Theoretically, the extra gyros wouldn't be necessary, although the alternative may be more expensive electronic active stabalization.

Again, thanks for the link!

Isaac Kuo

The body has no tail rotor, but a simple fixed fin can resist spinning down to a slower rate even in hover. For a robot, I think a constantly rotating body can be an advantage--for example, a single sonar sensor can sweep all around. Thus, I was thinking of a robot with 4 long spindly wire legs each with a fixed fin at the end for symmetry. With this symmetry, the body would slowly rotate even in "forward" flight.

In RC helicopters, some simpler models feature a fixed tail fin instead of a rotor. These require forward flight to stop spinning, and are more or less uncontrollable (by humans) in hover due to the constant spinning.

The essential principle is the same. If you removed the tail motor and rotor, and replaced them with a fixed fin, then you end up with the idea I was wondering about.

Isaac Kuo

Hmmmm. As long as you are sticking something out in the air to slow rotation, it might as well be another rotor. That way you can get some lift from it.

True enough, but maybe there are some simple ways around the problems.

I wasn't aware of these limitations. Perhaps a gyro is more trouble than its worth.

Maybe some sort of external information could be used to determine orientation. For example, a sideways pointing IR sensor could be attached to the rotor shaft. It detects the signal of a beam aimed at the robot. The periodic "pinging" of the IR sensor gives the robot a sense of the blade's orientation with respect to the fixed position of the beam source. That's enough information to determine when to pulse the motor for cyclic control. The actual orientation of the body isn't very important.

This I disagree with. If the main body is roughly rotationally symmetric like a hockey puck, the gyroscopic effect will actually tend to help stabalize its axis.

It certainly "wastes" effort to spin the fixed fins--this pushes air around to no good effect (or minimal good effect if the fixed fins are angled a bit). However, a traditional helicopter also "wastes" effort pushing air around with the tail rotor.

These are disadvantages, of course, but may be worth it for the sake of eliminating the cost added by a tail rotor.

There are different degrees of "susceptable to winds". A helium balloon craft is susceptable to a degree which makes them pretty useless outdoors. I don't think this sort of craft would be so susceptable.

Sorry, I don't have any references in mind, just an understanding of the basic principle. Rotor blade efficiency goes up with radius, depending on the airspeeds and loading involved, but that's not anywhere near the whole story. When comparing two rotors vs one, there's an obvious question of how to compare them. Equal cost? Equal mass? Equal total length? And then there's questions of layout, power distribution, two engines vs one, etc...

It's just not a cut-and-dried formula, clearly. There are a bunch of different considerations involved, and the answer depends upon the particular circumstances and design constraints involved. Sometimes, multiple lifting rotors are better. The overwhelming majority of the time, one lifting rotor is better.

Yes, a small surface on the end of a long boom can turn the slightest breeze into a lot of torque. I hope that a symmetric boom/fin arrangement in 4 corners of a square can mitigate the problem. Also, perhaps the control system can reduce the significance of the problem.

I think I'd need to be more clever by half to get this idea to work. That's why I was asking if others had already done it.

My only robotic experience has been with slow and clunky ground robots propelled by modified R/C servos. I've even never flown an R/C helicopter, only simple R/C planes.

Anyway, the Keyence Revolutor would be the most obvious place to start. It already has the "Super Cyclic" control system, and it may even be possible to modify the IR timing sensor to a sideways pointing shaft mounted sensor.

I think it'd be a shame to mess with such a tight little package, though.

Isaac Kuo

Here is a suggestion:

Build a mock up of it, attach it to some sort of bi-axial force sensor, and take it into an environment that emulates where you expect to be able to use it.

When I was flying my Hummingbird indoors, drafts from air conditioner ducts would send me off course. This led me to strip of off the canopy for example.

If you go to the trouble of distributing your mass in a hockey puck fashion, you are preparing it for the rigors of dynamic balence. If you get wobble, then you have proven the necesity for better control over mass distribution. What speed do you propose spinning the fuselage at? You could simulate this as well, with some rotor blades and a motor.