Eddy Current Speedometer Experiment

In summary, the conversation revolves around creating an experiment using a motor driven shaft to measure the angular velocity of another shaft through eddy currents. The participants mention using 8mm shafts, pillow bearings, and ceramic magnets, but are not seeing any torque on a non-ferrous metal attached to a staff. They discuss trying different materials such as aluminum cans, copper coils, and aluminum plating, and question if they need thicker sheet metal, stronger magnets, or a different geometry. They also mention the importance of a good magnetic circuit and the orientation of the magnets. The concept of eddy currents and their effects are also brought up.
  • #1
Thomas Rugh
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Trying to create an experiment that utilizes a motor driven shaft to measure the angular velocity of another shaft via eddy currents. We made a mock experiment that uses 8mm shafts, pillow bearings, and ceramic magnets from home depot, but don't see a torque on a non-ferrous metal attached to a staff.

We tried using aluminum cans, copper coils wrapped around the diameter, and are about to try aluminum plating. The ceramic magnets have their poles orientated as seen in the diagram. The motor spins at 550 rpm, but we can't see the slightest torque being produced nor feel anything if we hold it by hand.

Do we need thicker sheet metal, stronger magnets, geometry, and/or have the magnets closer? Are we overestimating the force that can be generated? Thanks in advanced.

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  • #2
Hi and welcome to PF. I have never tried to make one of these but I have (distant past) taken a car speedo apart so I recognise the parts.
It is easy to underestimate the design effort in an everyday bit of old technology and there are some important features required for the system to work. You need a good magnetic circuit, involving the bar magnet and a steel cup (for a 'return path') with a small gap in which the aluminium cup can rotate. It is the field, sweeping across the thickness of the aluminium cup that generates the eddy currents.
You don't show a diagram of your actual setup so I am assuming that this is what could be wrong. You mention magnets (plural). The classic arrangement is a single bar magnet so what is your design? Do you have your ceramic magnets orientated the right way and do you have a very small gap between magnet and aluminium disc?
The eddy current effect with powerful modern magnets is usually very easily demonstrated. If you drop a magnet down through a copper tube, the eddy currents will produce a definite braking effect - so the force is significant. (If the tube has an insulating slot running down it, there is no braking effect.
I suggest you Google around for "eddy current experiments" and that should give you some ideas.
Edit: PS I googled around and, of course, modern super magnets are strong enough to show eddy current effects all over the place. Much more than the magnets I played with as a boy,
 
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1. What is an eddy current speedometer experiment?

An eddy current speedometer experiment is a scientific experiment that investigates the relationship between the speed of a moving object and the strength of eddy currents induced in a conductive material. It is used to measure the speed of moving objects, such as vehicles, by detecting changes in the eddy currents produced by the object's movement.

2. How does an eddy current speedometer work?

An eddy current speedometer works by using a coil of wire and a magnet. When a conductive material, such as a metal plate, is placed near the coil, it creates eddy currents in the material. As the conductive material moves, the strength of the eddy currents changes, which can be detected by the coil. The changes in the eddy currents correspond to the speed of the moving object, allowing the speed to be measured.

3. What are the advantages of using an eddy current speedometer?

One advantage of using an eddy current speedometer is that it is non-contact, meaning it does not physically touch the moving object. This makes it less prone to wear and tear and allows for more accurate and consistent measurements. Additionally, eddy current speedometers can be used in a variety of environments, such as extreme temperatures and high speeds.

4. What are the limitations of an eddy current speedometer?

One limitation of an eddy current speedometer is that it can only measure the speed of conductive objects. It also requires a relatively close distance between the object and the coil, making it less effective for measuring objects at a distance. The accuracy of the speedometer can also be affected by external factors such as electromagnetic interference.

5. How can the results of an eddy current speedometer experiment be used?

The results of an eddy current speedometer experiment can be used to calibrate and improve the performance of speedometers in various devices, such as cars and trains. They can also be used to study the effects of different materials and conditions on the strength of eddy currents, providing valuable insights for materials science and engineering applications.

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