My granddaughter is in Middle School and it is that time of year for science projects. One popular engineering project is a Catapult. So we’ve been working together to create a model catapult. Here is the SketchUp design, and this is a model of a DaVinci Style example, where the energy is stored in these perpendicular sticks (we used ash as a material).

Here is a picture of our first build, and it works quite well in shooting a ball about 20 feet.

There are plenty of pictures of these catapults online and in the 3D warehouse. Also there are a multitude of different styles and ways of storing energy. We used a Leonardo DiVinci style catapult that stores energy in two strips of ash.

As frequently the case, we started the SketchUp modeling with a photograph. Here I show how the tracing of shapes over the photograph provides enough information to make the components.

Now to the ratchet wheel. This is a close-up of the set-up to re-create this ratchet wheel.

There are 18 teeth, so I set the Circle Tool to 18 sides (24 is the default value). I placed circles to match both the outer and inner points of the teeth. Then I drew radii and the shape of the tooth.

After deleting much of the waste material, I was left with one tooth having a face. I copy-rotated that tooth as shown below using the Rotate Tool, after tapping the Ctrl Key (Option on the Mac).

Then I typed “x17” to complete the number of teeth in the ratchet. After deleting the waste radii, adding a 3/8-in. hole in the center, I pulled out the thickness of 5/8-in. completing the ratchet model.

And here is the video.

Tim

@KillenWOOD

Launch Gallery