How do gyroscopes work?

In order to understand how gyroscopes work, it's best to first explain what traditional gyroscope is. A gyroscope is a spinning disk contained in some sort of cage, ideally the disk made from a heavy material. The shape and the size of the disk is important. The optimum design is to have most of the weight on the outside. Hence gyroscopes often have a disk with a bulbous edge.

Once the gyroscope is spinning, it has a number of interesting properties. The first thing to note is that a gyroscope wants to continue pointing the same direction. This is useful in a number of applications in including navigating (gyrocompasses). However, if a gyroscope is pushed on one of either two axis, it will create a counter force perpendicular to the force being applied. This is known as a precession, it can also be known as gyroscopic couple or gyroscopic torque.

What is precession in gyroscopes?

Precession is the force that stops a spinning toy gyroscope immediately falling over. Toy gyroscopes often come with a tower/pedestal to place the gyroscope on. Once the gyroscope is spin up and placed on the tower the gyroscope will then tilt over slightly and rotate around the tower, it will eventually falling off but this is often after a surprising long time. These movements can seem strange and unintuitive. What is happening is that as the gyroscope starts to lean over gravity exerts a force on the gyroscope pulling it down, this causes the gyroscope to precess perpendicular to gravity, hence the motion around the pedestal. If you start the gyroscope spinning in the other direction or simply balance use the other end of the gyroscope to balance on the tower it will precess in the other direction.

If you add extra weight (that is not spinning) to the gyroscope, this increases the processional force and the gyroscope will rotate faster around pedestal. Another factor is the speed at which the disc is rotating, if the gyroscope is spinning at high RPMs, the gyroscope will process relatively slowly around the pedestal, but as the gyroscope slows down you will see the precession to be fast and it will fall over quickly.