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20 May 2024 20:05
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Welcome to the gyroscope forum. If you have a question about gyroscopes in general,
want to know how they work, or what they can be used for then you can leave your question here for others to answer.
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Question |
| Asked by: |
John Bourne |
| Subject: |
what is forced precession |
| Question: |
What is the definition of forced precession and free precession? I would like to know what each means and perhaps an example for each case. |
| Date: |
13 October 2004
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Answers (Ordered by Date)
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| Answer: |
Sandy kidd - 20/10/2004 07:33:43
| | | John,
I will attempt to explain this as simply as possible.
When a gyroscopic system (i.e. the gyroscope and the shaft that supports it) is rotated around a fixed point, the radial acceleration generates a torque across the gyroscope at right angles to the plane of rotation.
Passive or Free Systems
In a passive system where the acceleration is gravitational the result is a motion which is called “nutation”.
In this case a force will be imparted on the gyroscope as it makes a radial descent due to gravitational acceleration. Reacting at right angles to this force, the gyroscope will move immediately to the left or right (depending on the direction of rotation of the gyroscope) The gyroscope now sensing a new direction of acceleration will move upwards, opposite to the original downward direction of acceleration, forming an inverted half looping motion to start the cycle again.
As a result of the torque generated across the gyroscope, the mass of the gyroscope will be transferred from the gyroscope and its support shaft, to act vertically downwards through the axis of precession rotation, displaying the gyroscope’s apparent magical ability to float in mid air.
The gyroscopic system will appear to move very smoothly despite this movement, and will continue to repeat the movement as long as the gyroscope has rotational energy.
The toy type of gyroscope that is spun up with a length of string is a good example of a passive or free gyroscope.
Forced Precession
In gyroscopic systems subjected to forced precession (i.e. instead of the gyroscope and gravity controlling the rate of precession), the system is forcibly rotated. A certain person wrongly called this action “Forced Precession” about 20 years ago, and we now appear to be stuck with it.
When the gyroscope, (really more of a flywheel in this context), is subjected to forced precession, the gyroscope is experiencing a continuous acceleration in the plane of system rotation only. There is no nutation present, consequently a torque is generated continuously across the gyroscope, at right angles to the plane of system rotation.
In this case the magical floating (or “saturation point”, I tend to call it) of the gyroscope can be made to happen at elevated system rotation speeds as required. This saturation point depends purely on the choice of rotation speed of the system (gyro and support shaft) and the rotation speed of the gyroscope required to reach it.
Be warned.
Unlike passive systems, this action should never be attempted on a single (or unbalanced) gyroscope system, as this could be very dangerous.
Gyroscopic systems subjected to forced precession are invariably experimental devices in the domain of inertial drive enthusiasts.
Sandy Kidd
20/10/04
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