Framing and Pen Centering

From Evil Mad Scientist Wiki
Jump to: navigation, search
eggbottiny.jpg This wiki page is part of the documentation for the Egg-Bot kit. Click here to return to the Egg-Bot overview.
The specifics of this portion assume that you have version 2.1.0 or higher of the Eggbot extensions installed.
Click here if you need help determining which version you have installed.


Learning to frame and center drawings on your eggs is simple and straightforward. It is also helpful to understand how the Eggbot positions your drawing relative to the pen's starting position plotting. Both of these topics are discussed here.

Let's get oriented[edit]

Before discussing framing, let us first orient ourselves. To help visualize the edges of the drawing page, display the page's boundaries via the "Document Properties" item of Inkscape's "File" menu. When Inkscape displays our drawing on our computer screen, the drawing page or template has a well defined top and bottom as well as a left and right. Figures near the top of the drawing are plotted near the headstock end of the egg so we'll refer to that end as the egg's top or top pole. (The headstock is the end of the Eggbot with the egg motor -- the motor which turns the egg.) The bottom of the Inkscape drawing plots near the tailstock end of the egg making that end the bottom or bottom pole of the egg. The Eggbot moves to the left or right in our drawing by rotating the egg. It moves up or down in our drawing by moving the pen arm.


First, keep in mind that the recommended template size of 3200 × 800 pixels is just a guideline. It's a good first approximation for laying out drawings. The actual top and bottom plotting limits -- the limits beyond which the pen arm cannot reach -- will vary with a number of factors including the shape and size of your egg, as well as its mounted position in the Eggbot frame. Even the shape, diameter, and holding position of the drawing pen can influence the plotting limits. The upshot of all of this is that some experimentation is needed to locate reasonable top and bottom drawing limits in your Inkscape drawing page. Given all the variables, there simply is no one template height that will always work perfectly. And, there is not even any obvious automatic electronic means of centering the pen or determining the plot range that accounts for all of this variability.

Fortunately, there is a simple and reliable procedure to get the plot framed and centered correctly every time. Follow this procedure and you can reliably fill the available plotting region to the extent possible.

1. In your Inkscape drawing, draw two short horizontal lines, one near the top of the drawing page, one near the bottom. Consider putting them in a separate layer labelled something like "1-test".

2. Plot this layer alone using the "Layers" tab of the Eggbot Control extension. If these two horizontal lines plot where you want them -- very close to but not hitting the physical limits --then you are good to go. Otherwise, adjust their positions and try plotting them again. Repeat this step until you achieve satisfaction.

3. Once these two limits are determined, position your drawing within the drawing page such that it extends from one line to the other: nicely centered and now filling up the available drawing region.

4. Delete the parallel "test" lines. Or, you can put your actual drawing in another layer, and then just plot that layer.

Pen centering[edit]

Warning: This discussion assumes that you are using v2.1.0 or later of the Eggbot Control extension. You can check which version you are running with the * tab of the Eggbot Control extension.

In the Eggbot Control extension, there is an option called "Start with pen centered". You can find this option on the "Options" tab. If it is not checked, then check it and click the "Apply" button.

So what does this option do? It tells the Eggbot that when you start a plot with either the "Plot" or "Layers" tab, that the pen is resting at the (x, y) point (W/2, H/2) in your drawing. Here W is the width of your drawing page (template) while H is its height. Often these are, respectively, the values 3200 and 800 pixels. If your drawing is vertically centered relative to the Inkscape drawing page, and you park the pen midway between the egg's top and bottom, then your drawing should be plotted well centered on your egg.

A word on aligning your artwork within a drawing page[edit]

For first time users of Inkscape, here are two methods to align your entire drawing within the drawing page.

1. Begin by selecting everything in your drawing with the "Select All" or "Select All in All Layers" items from the "Edit" menu. From the "Object" menu, select the "Align and Distribute" item. A new window pane should appear on the left side of the Inkscape window. In this pane, find the "Relative to" item. Select "Page" to indicate that we will align everything relative to the page. Next, check the "Treat selection as group" checkbox. Finally, to vertically align your drawing, click the vertical centering icon: that's icon is the third from the left in the second row of icons (below the "Treat selection as group" checkbox).

2. To instead manually align your artwork, again begin by using "Select All" or "Select All in All Layers" from the "Edit" menu. Next, activate the "Selection" tool from the left edge of the Inkscape window. That's the tool whose icon is a pointer; it should be the top most tool in the vertical stack of tools along the left edge. With that tool selected, then click in your drawing page and, while holding the mouse button down, drag the selection to align it.