website: Add controls page

wobsite/controls.md

+---
+layout: default
+---
+# Quadcopter PID Controllers
+
+The quadcopter is stabilized with on-board PID controllers. These controllers
+use pitch, roll, and yaw data from on-board sensors and positional data from the
+infrared tracking system to determine appropriate actuator signals necessary
+to keep the quadcopter stable during flight.
+
+The classical PID controller is characterized by 3 coefficients that specify
+how the controller functions. A PID controller can be configured through
+iterative determination of the PID coefficients, but we expect to obtain a more
+accurate control system by first developing a robust mathematical model of the
+quadcopter system. Once we establish this model, we can use numerical
+characteristics of the quadcopter to calculate the appropriate PID coefficients
+for our controllers.
+
+The model we are developing follows the methods developed by our advising
+graduate student Matt Rich in his thesis [Model development, system
+identification, and control of a quadrotor helicopter][1].
+
+
+
+[1]: http://lib.dr.iastate.edu/etd/12770/
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