My kids love the Syma S107 toy helicopters, which cost just $20 and are amazingly stable. The big breakthrough for this generation of toy helicopters was the introduction of gyros, but I just took apart a broken one and was impressed to see that it has just ONE gyro (circled in black above), mounted vertically.
I know that the coaxial props create a natural mechanical stability in the XY direction, and I assume that gyro is stabilizing in the Z (yaw) direction. But is it really as simple as that? The stability is astounding. They're just motionless in the air until you budge the sticks.
BTW, there are no magic sensors on the bottom of the board, either:
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My daughter and I each have a EagleJet from Protocol..pretty much the same copter with RF control. They are amazingly stable..indoors. There has to be absolutely no wind to fly it outside. The winning Pixhawk 2009 machine uses the LAMA 400 counter rotating mechanics, top blades with stabilizer but with swashplate on lower blades for directional control...Much simpler stability requirements compared to other methods as it helped them win the 2009 indoor autonomy competition :)
Doug is correct,
If you use a co-ax heli withough a gyro they are still quite stable but the yaw axis drifts even after trimming
Many of this style coaxial helicopter have excellent stability, due to the large stabilizer weights and long bar on which the stabilizer weights are suspended. Also, the tall mast adds to the stability. Many manufacturers have had great stability with this setup even before the introduction of small/cheap gyros. Of course, the mechanical stability comes with a price. They have very limited forward speed and other than yaw control have almost no maneuverability.
What Veikko said was true, but there are no swashplates or paddles on my Syma. The flybar on the S107 is gyroscopic, and changes the pitch of the upper rotor to counteract any movement relative to the lower rotor and fuselage. It is an elegant solution. That they can sell these at retail for $20 is astounding.
Chris, I have one of those little guys as well and am astounded at the stability. I really believe that you gain a lot with the counterbalances in plane with the top rotor. if you play with the heli in your hand with the throttle on, you can tell it's counteracting outside disturbances pretty well in the pitch and roll rotations. Remove those little suckers and I bet it wouldn't fly well at all!
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