Sunday, December 13, 2009

Designing in Sketchup


In my Principles of Technology class, we're using Sketchup to design the parts we will make for the Mendocino Motor. Though we'll fabricate the parts with hand and power tools, you can also use Sketchup to make the files needed to cut parts on a mill, Makerbot, Shopbot or other CNC tools.

The Mendocino Motor project appears in the Teachers' Pet Projects section in MAKE, Volume 20, page 79.

Here are some techniques to design parts for the motor:

First get familiar with the Sketchup interface. This is pretty easy, the software is rather intuitive. A good place to start is by making whole shapes with the rectangle and circle tools. Draw a shape, then use the Push/Pull tool to extrude it up or down. You can make a shape on the side of another shape, then pull it out or push it in. Make some shapes. Mouse over the tool icons and you should see the name of the tool in a popup.

You can also do some neat stuff with the Move tool. If you have a cube, draw a line at the midpoints (again, mouse over, and watch for the popups). If you pull the line up with the Move tool. This will give you something that looks a lot like a roof of a house on the cube. If you pay attention to the color of the line while you are moving it, you'll see that it takes on the color of the blue axis if you are pulling straight up. This means that you are moving parallel to the Z or vertical axis.

As the designers made the software easy to use, it is not very straightforward to resize objects and move features. Some other CAD software packages, such as ProDesktop, ProEngineer, Blender, Solidworks, AutoCAD, Rhino and more definitely do have measurement features that are probably easier to access. In general, these other packages are harder to learn, a tradeoff for their greater precision and parametric features. These other software packages (excepting Blender) will also set you back more than a few bucks, though most offer student/educator versions and discounts to help out some of us.

To get a more accurate design out of Sketchup, you'll want to start paying attention to the measurement box on the bottom right side of the screen. If you make a rectangle and then type in the dimensions you want it to be and hit the enter key, the rectangle will be the size you specified. For reference, I've made a set of screenshots of just about all the steps taken in this tutorial. The tools themselves are not shown on the screenshot, but you can tell which tool is being used by looking at the icons in the toolbar. The measurements of all the parts are listed on the MendoMeasurements page of the course's wiki.

For the base of the motor, we need to make a 3 3/4 by 9 inch rectangle. Draw any rectangle to the right of the origin intersection. Immediately after, type the size, 9, 3 3/4 or 9, 3.75 and hit enter. The rectangle should be resized along the x axis. The first number is the distance along the x axis, the comma separates the x and y values, and the second number is the distance along the y axis. You can check the measurements with the Tape Measure tool.

Next, we'll want to extrude the shape up 3/4 of an inch. To do this, we use the Push/Pull tool. Switch to the tool, then hover over the rectangle. You will see the shading change. Click the mouse and push up any distance. To size the extrusion, type 3/4 or .75 and hit the enter key.

To place the grooves that the magnets will sit in, we need to make some guides. The grooves will be half of the thickness of the wood, or 3/8" and they will be 1/2" thick. Use the Tape Measure tool to make the guide. In the tool, first click on the bottom or top edge of the shape. Drag down and type 3/8 to place the line. It should be a dotted line. On the front edge of the block, make a guide that is 2 1/4" from either end. To locate the other side of the groove, measure towards the middle of the block 1/2" and place another guideline. Next, use the Line drawing tool that looks like a pencil to draw in the three lines of the groove. Once the lines are in place, you can use the Push/Pull tool to remove the material of the groove. Once the file is complete, save it as BaseWithGrooves.skp.

The next two parts are easy to make in Sketchup. The upright is 3 3/4 square and 3/4" thick. When you make the rectangle to start the part, put the coordinates in as 3 3/4, 3/4. This will save you from having to rotate it later. Use the Push/Pull tool to extrude it up to 3 3/4. Save this file as Upright.skp. To make the mirror, use the same process. Make the rectangle with the measurements of 3 3/4, 1/8 and then push it up to 3 3/4. Save this file as Mirror.skp.

Now you have three parts that you have designed. To put them together, you create a new file that you will save as BaseAssembly.skp. Bring in the first part you made, BaseWithGrooves.skp. Place the part at the origin of the three axes. It should snap into place at the origin. While the part is selected, you can go to the Edit menu and Lock the component. This will keep it from moving around later.

Next, you bring in the Upright.skp. Go to the File menu and choose Import. Then find the part. If you also place this part at the origin, you can move it into place with the move tool. You can also eyeball its placement, but let's go for accuracy. Use the Orbit tool to move the view around so you are looking at the origin. You can roll the scroll wheel on the mouse to zoom in and out, or you can use the zoom tool. Click on the upright component with the Move tool, it should have a blue box around it. Select the bottom corner closest to the origin of the axes. Move it up on the Blue axis a bit and type in 3/4. This should place it on the top of the BaseWithGrooves part.

To place the Mirror.skp part, do the same thing. Import the part and place it at the origin. Move it up 3/4" and then move it along the RED? axis 3/4" It should be now placed on top of the BaseWithGrooves and alongside the Mirror part. Save the file.

You can also do some neat visual styling of the parts by selecting them and using the paint bucket tool to color them. If you want to color one face different from the others, you will need to select the part, then go to the Edit menu and choose Explode. This will allow you to change the part, even paint the faces different colors and more.