Solving For Gears

Hot Off the Printer

Gears are categorized as one of the basic machines, tools that make our lives easier by reducing the amount of work or effort a human needs to put in when accomplishing a task. Levers, pulleys, wheels, and other simple constructs let us lift, move, and rotate objects long before we could harness power. They can also make 3D printed projects more fun.

Say, for instance, you wanted to make a small parade of penguins (what, just me?). Putting them atop a platform set on gears would be a great way to make them rotate in a little circle, adding dynamics.

But gears can be a little tricky. You have to consider direction, spacing, and speed before building your model.

Direction. Looking at how gears fit together, one pushes the other using the little teeth. So if the big gear spins clockwise, its teeth would catch the teeth of the small gear and push the small gear counterclockwise. If there were another gear beyond the small gear, the teeth from the small gear would then push the next gear to spin clockwise again.

Spacing. Gears are sensitive, and can jam up if the teeth aren’t properly aligned. If two teeth hit head on – instead of one gear’s tooth fitting into the space between the next gear’s teeth – or more than one tooth can fit into a space but not quite two, there could be a jam. Similarly, if the gears are too close together or too far apart, the machine might get jammed or start to slip. Creating uniform gears and situating them in fixed positions can resolve these issues.

Note that if you are using Tinkercad to create your design, there are gear options to help make your pieces fit together. Be sure to add a piece to hold the gear in place, and ensure this piece in the exact center using the align tool. If the gear is fixed off-center, the entire gear will move in a small circle while rotating and will not fit properly with the rest of the machine.

Speed. We don’t want to send our penguins flying, since they are land birds, so we should mind our speed. We want to keep the first gear a comfortable size that one finger can complete the rotation without lifting, but it might be cool to have the penguins parade a little faster. Gear speed for two gears next to each other depends on the number of teeth, not necessarily the size of the gear. The relative speeds of the gears is inversely proportional to the number of teeth on each gear (this is known as the gear ratio). So if the input (where the energy goes in) gear has 30 teeth and the output (in our case, the penguins) gear has 10, the speed of the penguins will be 3 times that of the finger gear. Because we also have to consider spacing of the teeth, it’s easier to make the gear with fewer teeth smaller to be sure they will line up properly.

So to get the penguins rotating in the same direction we spin our finger but twice as fast, we need three gears: the input gear where we put the energy in, a middle gear with the same number of teeth as the input to rotate in the other direction, and the output gear with half as many teeth as the middle gear to double the speed while rotating in the initial direction. Now we create a base for these gears to keep them spaced properly, and pegs to hold the platform of penguins, and we are in business to print.

After all of that, creating the actual penguins and the supports for the wings and beaks wasn’t so bad! But now we have a little parade, using a simple gear machine.