Add short research report for step 2

Fixes #3

initial_design/exploration/design_space_exploration.md

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+# Design space exploration
+
+## Introduction
+This document is a summary of the design space exploration.
+We are looking for ideas that can help us in our design of the whiteboard writer.
+This is looking for existing projects but also for different types of plotters.
+
+We are just searching on the internet. The summary is found in the next section.
+
+## Exploring
+
+### Image search
+Searching for `whiteboard writer robot` gives the following ideas:
+- [iboardbot (kickstarter)](https://www.kickstarter.com/projects/879074320/iboardbot-the-internet-controlled-whiteboard-robot)
+Plotter type robot. With Cartesian axis. But can also done with a different axis like [this](https://www.youtube.com/watch?v=5492ZjivAQ0), which shows some nice solution for the cabling.
+- [Scribit (kickstarter)](https://www.kickstarter.com/projects/1864378255/scribit-turn-your-wall-into-an-interactive-canvas)
+Kiting plotter robot. Suspended with two wires. Also this simple [example](https://www.youtube.com/watch?v=GgOi8WaNoIs), which clearly shows some design issues.
+- [Robot Portrait (youtube)](https://www.youtube.com/watch?v=FQfnpJm8fqw)
+Polar axis plotter robot.
+- [Robot Clock](https://www.youtube.com/watch?v=4QgeQAiSmM8)
+Simple clock with scissor arms.
+- [Doodle Clock (youtube)](https://www.youtube.com/watch?v=MmIP156JIxg)
+Articulating arm. With a lifting boom and rotation arm/link
+
+#### Observation.
+All systems are slow.
+Most have the problem of being 'heavy' and moving the arm quite some distance.
+The interesting one is definitely the kiting robot. It can be easily constructed but has still some design issues.
+It has de tendency to swing.
+Light models are quicker but in that case the oscillation of suspension wire becomes more dominant.
+
+