The Inner Workings of Magna Doodle

In 1974, a team of four engineers from Pilot Pen Corporation created a "dustless chalkboard." This innovation has grown into one of the most beloved drawing toys, with over 40 million units sold since its debut. Generations of children have found joy and education through this remarkable tool.

This incredible creation is none other than the Magna Doodle!

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In this article, we’ll explore the inner workings of this captivating toy and uncover how it functions.

Inside a Magna Doodle

The Magna Doodle is essentially a magnetic drawing board. It consists of the following components:

To use the Magna Doodle, simply write on its surface using the magnetic pen. When it’s time to erase, move the sliding magnet in either direction—it works seamlessly both ways.

Now, let’s dive deeper into each component.

The Heart of It All

The magnetophoretic display panel is the feature that sets the Magna Doodle apart.

This magnetic display is structured as follows:

The walls of the honeycombed lattice in the middle are thinner than 0.02 inches (0.5 mm). Each compartment in the lattice contains a dense liquid suspension or dispersion medium packed with tiny magnetic particles. The liquid medium is formulated so that the particles move through it when influenced by magnetic forces from the pen or eraser, but they remain unaffected by gravity. This is achieved through specific properties of the liquid:

The lattice structure of the middle layer ensures the magnetic particles are evenly spread across the entire display surface.

Now that we’ve explored the display, let’s examine the pen.

Magnetic Pen

The magnetic pen is a straightforward plastic tool with a small magnet embedded in its tip. Its magnetic field is powerful enough to pass through the plastic and move the particles within the thick liquid.

The magnetic pen is designed with ergonomics in mind, making it easy for anyone, particularly young children, to hold comfortably. It is typically connected to the Magna Doodle by a string. Some versions of the Magna Doodle also include "shape stampers," which are magnets shaped like diamonds, triangles, and circles.

While writing is a key feature of the Magna Doodle, erasing is equally important. Let’s take a closer look at the eraser.

Magnetic Eraser

The magnetic eraser is made up of a bar magnet housed within a plastic slider.

The magnetic eraser is positioned at the back of the Magna Doodle, hidden behind the display and invisible from the front. It slides smoothly within a groove on the case, allowing it to move from side to side effortlessly.

Now, let’s examine the last part: the case.

The Case

The plastic case serves as the framework that holds all components together.

It consists of two main parts:

A front piece that:

A raised back piece that:

Now that we’ve examined each component, let’s see how the Magna Doodle operates!

In Action

Let’s slide the magnetic eraser across the Magna Doodle to begin with a fresh, blank display. The front appears clear (white), while the back holds all the particles, which were drawn to the rear by the magnetic eraser.

Upon closer inspection of each cell, you’ll notice the magnetic eraser has aligned the particles to one side!

Now, as you move the magnetic pen across the display, the pen’s magnet attracts the tiny particles from the back to the front, creating a visible line. Notice how the magnet draws particles from neighboring cells and aligns them in the direction of movement (in this case, to the right).

Since the particles are lightweight and the liquid dispersion medium is viscous, gravity won’t pull the particles forming the lines back to the opposite side. The writing remains stable and undisturbed.

To erase the display, slide the magnetic eraser across the back. As it moves, the eraser pulls the particles forming the lines from the front to the back, aligning them in the direction of the movement. The thickness of the liquid medium ensures the particles don’t float back, keeping the front side clean.

The Magna Doodle is an exceptional toy that enables children (and adults) to draw and erase pictures and words endlessly without wasting paper or generating chalk dust. It’s perfect for long car trips, allowing hours of creativity without producing trash or needing to sharpen pencils. Teachers have utilized Magna Doodles to assist students in practicing writing and learning new words. Additionally, Magna Doodles have found surprising applications in various settings: