A experiment to confirm gyroscopes maintain their centre of
If any form of propulsion from a gyroscope is to succeed the centre of gravity
of the device needs change. This change needs to occur after a full cycle of the
device and without interaction with surfaces or air movement. Many people
seem to be trying in vain to produce complex devices without the full
understanding of single gyroscope. This seems an illogical and unscientific
approach to me. If there are undiscovered forces/attributes of gyroscopes,
they will be present in a single gyroscope. I decided to run a simple experiment
with a single gyroscope to see if I could prove or disprove whether the centre
of gravity changes in a gyroscope. There didn‟t seem to be any independent
tests on Prof Laithwaite‟s experiment, at least not publically so I decided to
reproduce one of his key experiments.
Images courtesy of the BBC
The experiment was shown by the BBC in the UK as part of the 1974-75
Christmas lectures which professor Laithwaite was presenting. He first spun up
a normal toy gyroscope and placed it on a tower (small stand). He then
suggested that because of the huge difference in weight of the tower (< 1
gram) and gyroscope (about 310 grams), that you may expect the gyroscope to
want to push the tower round itself, rather than the gyroscope precessing
around the tower. He did make the audience aware this couldn‟t happen
because of friction of the tower with the table/box it was on. So he proceeded
to do another experiment this time by placing the tower on a small piece of ice
which was on a wet plastic sheet. The tower did keep still while gyroscope
precessed around it. When I first viewed this video I conducted that same
experiment with mixed results. Sometimes the ice would move, sometimes it
wouldn‟t. It was very hard to keep the whole thing level and I‟m convinced the
vibrations of the toy gyro had an impact. However, it inspired me to take the
experiment further and reproduce it more scientific and precisely.
It was a few years later before I had all the equipment and time to conduct an
experiment. On the 21/11/2005 I ran the experiment.
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The equipment and configuration
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A solid aluminium frame with three height adjustable feet to used keep
structure level and generally stable.
An engineering spirit level is shown on the right of the aluminium
frame to ensure everything is level (all axis have been checked).
A hi-resolution SLR camera with wired remote triggering. The picture
shown was taken using this camera which was mounted on a tripod.
The camera is automatically triggered whenever the shaft reaches a
certain position at each rotation of the gyroscope around the main
shaft.
Very high torque servo motor (oblong black object left to the main
shaft) which can turn the shaft accurately to a few degrees (excluding
slack in belt) and turn the shaft at hundreds of rpm.
Aluminium timing gears on the servo, shaft and digital sensor
Rubber coated steel wire timing belts to reduce stretching and stop
slipping
Digital sensor (small square object right to the main shaft) that can
detect 128 positions per 360 degrees (accurate to about 2.8 degrees)
Precision linear bearing allowing the structure to slide freely along a rail
attached to the aluminium frame. Seen just above the ruler attached to
the frame.
Stainless steel shaft, gyroscope, ring, arm (drilled to reduce weight) and
hinge.
Hinge is custom made from stainless steel and has bearings either side
of the „pin‟
LCD screen for feedback. Information can be capture when the
camera is trigger
Ruler fixed on the frame to show the movement
Atmel AVR chip, programmed by myself. Collects information from
the sensor and controls speed of servo and when a picture is taken.
Note: There is a second servo and linear bearing on the arm. This is in a fixed
position. It was not used here and is intended for another experiment.
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The experiment
The experiment is performed in two parts and the results compared. In the
first experiment the gyroscope is spun up using an electric drill (not shown)
and allowed to precess around the main shaft (vertical). The arm it is attached
to is free to move. The servo motor‟s belt is disconnected but removed. It is
important not to remove the belt in order to keep the weight the same in both
parts of the experiment. The sensor constantly measures the speed of
gyroscope precessing around the main shaft. The chip displays the speed,
position and time on the LCD. Every 180 degrees the chip triggers the camera
to take a picture. The pictures record the speed, position (both visual and from
the LCD), angle of the arm, time and crucially how far the whole structure has
travelled along the linear bearing/rail. The rpm of gyroscope is measured using
a laser tachometer before and after.
The second part is nearly the same as the first except gyroscope is NOT
spinning. All other aspects are kept as close as possible to the first part.
So the arm is locked into position at the same angle as when it was precessing.
The gyroscope is rotated around the shaft using the servo motor at the same
speed as when it was precessing (this can be confirmed by the sensor/LCD
readout). Again the camera records all the information at 180 degree positions
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Results
<need to put pictures here>
When precessing (first part) it started at 11.7cm and after 180 degrees ended at
11cm: a difference of 0.7cm. The gyroscope rpm was about 5000rpm and took
about. 1.4 seconds to precess. When the gyroscope was rotated by the servo
motor (second part) it started at 12.9cm and ended at 12.6cm: a difference of
0.3cm. This is contrary to Professor Laithwaite experiment with the ice. In
other words when the gyroscope was spinning the C of G moved more.
Reducing the rpm of the gyroscope causes it to precess faster round
the main shaft. When I did this I could get movements of centimetres rather
than millimetres. Interestingly at this high precessional speeds the results
reversed with the precessing gyroscope moving less.
Synopsis
There were a few things that could have caused inaccuracies with the
experiment. Firstly the camera could not take pictures in real-time.
In other words there was a delay taking the picture, because on occasions it
was trying to take pictures too quickly. However, then this happened it showed
up on the picture (LCD time + position of gyroscope).
Second, there was some small amount of „play‟ in some of the joints.
This caused only a few millimetres of movement in at the top of the device
when a pressure is applied. All things considered, I believe this was quite
minimal and not cause much disruption.
Thirdly measuring/setting the angle of the arm was not as accurate as I
would have liked. I measured it in on the computer from the photos and set it
by putting a wedge under the arm. Although not 100% accurate I felt it was
enough.
Four. Wires for the servo and sensor could have added extra friction. I
dismissed this because they are very thin flexible wires and they were present
for both parts of the experiment.
Five. The gyro was spinning for the first part and not for the other.
When the gyro spins it can does cause air movement close to the disk. So the
aerodynamics would be slightly different for both parts of the experiment.
Again I feel this is very minor consider the mass involve.
Six. The most worrying and the most likely candidate to explain the difference
between the two sets of results is what I would call “Slip-stick”. Again this is to
do with play in the joints, but rather than cause movement it causes extra
friction during part of the cycle; specifically in the linear bearing.
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For example, the structure maybe at the furthest point on the left of
the rail. The gyroscope starts to precess causing it to move along the rail to the
right. The weight is going through the pivot point of the arm so the weight is
pressing vertically down on the linear bearing. It moves freely along the
bearing. However, in the second part of the experiment the gyroscope is not
precessing (being turned by the servo) and the weight is levering the linear
bearing. This could cause it to „stick‟ at some points of the rotation more than
others ( The linear bearing with have higher friction when the load is at right
angles to the direction of the rail).
Possible improvements to the experiment
1) Add a new section of the frame above the gyroscope/structure in
parallel with the bottom section and then add a second linear bearing
above the gyroscope. Provided this is connected probably it should
dramatically reduce the “slip-stick”.
2) Add a sensor to detect the movement along the rail. This could be
recorded and the two parts of the experiment compared. This would
light WHERE in the rotation any irregularities are occurring.
3) Increase the number of pictures per second the camera can take.
4) Add a angle gauge to the arm (in degrees)
5) Possibly contain the gyroscope in a light container to stop aerodynamic
irregularities.
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