Research Progress Note 1: Inertioid Research at Stanford
19 August 2000
Chris Duffield, Materials Science & Engineering Department [through March
in cooperation with Vladimir Poponin (International Space Sciences
Organization, International Frontier Science Study Group), and Gennady Shipov.
When ISSO physicist Vladimir
Poponin and visiting physicist Gennady Shipov showed me a video of the old film
of Russian engineer Vladimir Tolchin’s inertioid experiments from the 1960s, I
was amazed. Here were moving images that seemed to demonstrate phenomena that
directly countered my physical intuition: forward or rotary motion without
physical reaction. I just had to try it myself.
My first attempt was to outfit a
toy truck with two stepper motors. The motors were mounted at the ends of a
crossbeam, axes vertical. They drove counter-rotating off-center weights, made
of metal washers held by nuts on bent L-shaped threaded rods. It seemed at times
to be demonstrating the effect of converting rotary motion directly into linear
motion, as in the Tolchin film. But I quickly encountered most of the
obstacles that must be overcome in this type of experiment:
- Canceling out gravity. The floor in my office was not level enough.
The apparatus showed me dips and rises in it that I had never noticed
- Eliminating friction. The wheels had too much of it. The swinging
weights had drag in the air.
- Eliminating other forces. The wheels where knobby, the cables to
the stepper motors exerted pull, and the wheels interfered if they were not
directly aligned with the thrust.
- Moving enough mass to make the effect larger than residual forces.
The stepper motors were limited in the torque they could apply. So the
masses I could use were limited in both weight and acceleration.
- Coordinating the angular position and motion of the two weights.
Tolchin used gears for this purpose. Stepper motors are precise, but can
lose their coordination when maximum torque is exceeded.
- Balancing the two weights and getting their paths coplanar.
Balancing took some careful adjusting. Co-planarity was my reason for
mounting the motors on a cross-beam.
- Aligning the thrust vector with the center of mass. The rotating
weights on my truck were above the center of mass, leading to a fore-and-aft
torque which caused it to buck with each rotation.
- Controlling the angular motion of the weights. Stepper motors allow
precise control of rotational position, speed, and acceleration, within
their torque limits. But I was also limited by the available functions of my
stepper controller. I wound up accelerating for half a rotation and
decelerating for the other half, with a stop in between. Other acceleration
profiles would be desirable.
I finished building this toy truck
inertioid one night in 1999, in time to show it to Poponin and visiting Russian
physicist and inertioid expert Gennady Shipov the next day. They were pleased,
and demonstrated to me Shipov’s own device, based on Tolchin’s design. It is
a small three-wheeled cart with spring-and-gear-driven almost-coaxial weights.
Its ratio of rotating mass to total mass was higher, so the effect was larger,
even at slower rotation speeds. Air friction seemed to be negligible. But the
main drawbacks of this device appeared to be a spring which quickly ran down,
unknown friction function of the wheels, and great sensitivity to tabletop
smoothness, flatness, and levelness. Nevertheless, under the best conditions,
this device appeared to show the three core phenomena of:
- jerking, stepping, forward motion without apparent net acceleration of
the center of mass.
- stopping without coasting when the weights stop, and
- reversing and returning, when pushed backwards as if by elastic
Later in 1999 I suggested to
Poponin that we test Shipov’s device on an air track in the Stanford physics
department Introductory Teaching Lab. I built a platform on top of two standard
air carts (needed to support the device’s weight), surrounded by clear plastic
walls to eliminate any differential air drag from rotating weights. I had a
transparent top to complete the enclosure, but we never used it.
Poponin brought Shipov’s device
back to Stanford. With it mounted on the platform, we turned the air track on
and leveled it. Then we wound up Shipov’s device and let it go from rest. It
appeared to demonstrate the effect beautifully. With back-and-forth movement, as
the weights rotated, the system stepped at apparently constant speed along the
air track. When it hit an elastic bumper at the end, it would bounce back a
little, then return to hit the bumper again and again. When the weights stopped
rotating, the system would almost come to rest.
At a second session in the
Stanford undergraduate physics lab, we mounted Shipov’s device on a square
sheet of Lucite plastic, and placed it on an air table. Nothing worked well. The
table did not appear to be level or flat enough, as the system wandered all over
the place. And we found that shifting the weight on the plastic square (
which happens every time the weights rotate) lifts one edge higher and provides
horizontal propulsion from more air escaping there.
This led us to suspect something
similar might be happening on the air track. Again we mounted Shipov’s device
on the air cart platform. I suggested that we disable the cam that caused the
rotating weights to accelerate and decelerate. They would now rotate at an even
(and gradually slowing) rate. Such a system’s center of mass should
theoretically move at a constant velocity. To our surprise and amusement, what
we observed was an apparent duplication of what we had seen with the
acceleration-deceleration cam in operation! Starting from rest, the system began
to move along the track, and after an elastic collision with the end bumper,
would bounce back and return again and again.
Looking at the system more
carefully, we noticed that asymmetries in the system were causing it to rock on
the air track. The rotating weights of the device were above the center of
gravity, resulting in periodic pitching torque. And the near-coaxial
configuration meant that the weights were not coplanar, resulting in periodic
rolling torque. Looking closely at the air cart, we saw that these rolling and
pitching torques were indeed causing the cart to twist relative to the track,
opening and closing the spaces between them and at times even allowing the cart
to touch the track. This combination of time-varying drag and air thrust meant
that our earlier observations were not a valid test of the inertioid effect.
Better systems need to be built to
properly carry out the experiment and explore the variable space of relative
weights, acceleration profiles, etc. This will take time, money, expert help,
and access to other facilities. The effect appears to be robust, but all
interferences must be reduced in order to remove any doubts.
Our easiest next step is to test
the same Shipov device by mounting it on an air puck running on a large flat
polished granite table at Stanford’s Aerospace Robotics Laboratory.
Preliminary quantitative position and angle data may be obtained by analyzing
video taken from an overhead camera.
Postscript 12-12-2000 -- In September and October I started experiments
again. This time I suspended a platform from a high rafter and mounted
stepper motors with weights on it. Much longer pendulum arm would be
desirable for future experiments. The weights jerking around interacted
with the pendulum oscillations in irregular ways. When I set the weight
rotation period approximately equal to the pendulum period, the result was
parametric amplification -- the pendulum swung farther and higher with each
oscillation, like a child on a swing. The results were not definitive, and
I was discouraged. With these motors and weights, the rotation and
acceleration/deceleration cannot be made fast enough to make pendulum
oscillation irrelevant, for this pendulum length. And much longer pendulum
length would have, if nothing else, friction effects with the air. I
decided to discontinue the experiments and wish Shipov's group well. The
definitive experiment will be to do experiments in microgravity vacuum
Thanks to Martin LaPointe, Introductory Teaching Lab Manager, Department of
Physics, Stanford University, for air track
access and construction help.