<Misc> re: Gyro Stabilizers

[Knute Ream <knute@xxxxxxxxx>]

At 09:08 PM 9/2/98 -0400, Steve D'Gerolamo wrote:
>Do any of the current high tech racers use gyro stabilizers (instead of or
>complemented by conventional stabilizer bars) to control body roll on the
>track?  Conceptually, this could be a massive flywheel mounted low and
>center on the car, rotating front to back on a shaft belt driven off a
>modified drivetrain.  The axis/shaft of the flywheel could be directly
>coupled via suspension links/mounts to the large chassis plates and the
>spinning mass help mitigate much of the chassis lean.  
>
>	   Spin a bicycle wheel weighing a few ounces a few hundred RPM and feel
>the force when you attempt to tilt it sideways...now imagine the effect of
>a rotating mass weighing 75-100 lbs (or more) spinning a few thousand
>RPM's.  SD

OK, I'll bite!

One of my other hobbies is radio-controlled helicopters, and one of the
things that puzzled me early on was the need for blade hinges on the rotor
head.  Heli rotors spin extremely fast (nearly supersonic tip speeds on
full-sized helis), and the gyroscopic forces are significant.  For those
less familiar with helicopters, cyclic pitch controls the basic left/right
& forward/backward movement of the helicopter by varying the pitch of each
blade as it spins around.  For instance, if you wanted to move right, you'd
increase the pitch when the blade is on the left side and decrease the
pitch when the blade is on the right.  The typical "chopping" sound that a
helicopter makes is directly due to the constantly changing pitch to
produce the desired forces.

Anyway:  (this rambling explanation does have a point)

Unless the rotor head allows the blades to pivot, whether with flex-hinges
or a teeter design, the gyroscopic precession produced by the forces of the
cyclic pitch causes some _really_ weird coupling problems.  With a fixed
(no hinges) rotor head, the change in direction of the aircraft is exactly
90 degrees out of phase with the desired response; the hinges make
everything come out OK by letting the rotor disc precess as it wants to,
without translating that torque to the main fuselage of the helicopter.

Now in english:  if you had a really big gyro in the car, mounted on a
vertical axis, it would indeed reduce body roll, but depending on the
direction of rotation, right turns would cause the nose to dive and left
turns would cause the nose to rise (or vice versa) which would be a very
bad thing for consistent over/under steering between left and right turns.
If you mount the gyro transversely (same axis direction as one of the
wheels of the car) the side effect is also a potentially severe problem;
body roll will contribute either to understeer or oversteer by inducing a
"yaw" force (spin) on the car, again depending on direction of gyro rotation.

Interesting idea, but there's no free lunch.  I'm curious, too-  has anyone
seen this attempted?  Sounds like an RX-7 with the governer disabled might
be quite a handful on the track...

- -Knute

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