Why do bar fidget spinners judder?

A perfectly round fidget spinner would exhibit what’s called the gyroscopic effect. It means that the perfectly round object (like a bicycle wheel) will continue to spin without any judder when you twist it. You’ll feel some resistance due to the air and the angular momentum but it should continue to spin smoothly on its axis of rotation.

The judder (some call it wobble) you feel is due to a spinner moving out the current plane of rotation.

Torque and Judder

Take a fidget spinner and hold it vertical and spin it. It spins freely because you’re not applying any torque. Now twist it left or right by rotating your hand.

What you are doing here is applying torque to the spinner. By applying torque to the spinner, the angular momentum of the spinner tries to chase the direction that you twisted the spinner in.

Because the inner race of a fidget spinner bearing is not totally static, the spinner vibrates back and forth along a separate axis.

This is what fidget spinner makers call judder and is perfectly normal in bar spinners because it’s far away from a circle or disc shape.

Don’t worry – It’s PERFECTLY NORMAL for any bar spinner.

Other people mistakenly call this “wobble.” We’ll clarify what wobble really is.

A tri spinner has a shape closer to a circle than a bar spinner.

Therefore, a tri will exhibit more of a gyroscopic effect and experience much less judder.

What is wobble in a fidget spinner?

So a well machined fidget spinner will be perfectly balanced. This will allow you to spin the fidget spinner and hold it out on a single finger easily.

In a wobble-free fidget spinner, the center button should remain static without any vibration because the weight is distributed equally.

However, not all fidget spinners are machined well. Imagine you take a bar fidget spinner and decide to take a 20 gram chunk out of one of the arms.

Don’t worry – imaginary fidget spinners are free 🙂

Now try to balance it on your finger. It will most likely fall off your finger on the undamaged side because of gravity exerting a larger force on that side of the arm. More weight = greater gravitational force.

Now put it on your finger again, but spin it this time before it has a chance to fall.

The rotational momentum of the spinner “fights” against gravity because the heavier arm is constantly moving in a circle which is why might not fall off your finger immediately.

However, the differential in weights will cause opposite forces along a different axis.

This causes the vibration of the entire device and is most noticeable when the button looks like it’s having a seizure.

That’s the main difference between wobble and judder in a fidget spinner.