Brian and I are moving forward at a good pace. As he wrote in his blog
, we have our processor board in hand and the IMU is on its way. Yeah!
I have been busy with a few tasks:
1. Aircraft selection.
I am pretty set on buying the AXN Floater Jet. It is inexpensive, durable (foam construction with pusher prop), and comes with aileron control. I will probably put in the order this weekend unless there are objections from Brian.
2. AHRS development
We would like to use our IMU as the basis for an AHRS (attitude-heading reference system). An AHRS is basically an inertial navigator without the position information. To get this to work I first need an alignment algorithm. The IMU would need to be stationary while the accelerometers and gyros make measurements. The accelerometers sense the gravity vector, and this information is used to determine the pitch and roll. The gyros measure the earth's rotation and, with the help of the pitch and roll information, determine the heading relative to true north. I understand the theory, but I haven't worked out the math yet. It should be a fun problem!
Once the AHRS is aligned, the accelerometer and gyro data is continuously integrated using the strapdown equations to provide the orientation of the aircraft. I have much of the AHRS code written already from a previous project. If it works remains to be seen! :-)
3. Simulation development
I did some searching and found a wonderful resource: Aerosim blockset for Simulink
. It is free for educational and non-profit users. It has all the 6-DOF equations, aerodynamic equations, environmental equations, etc, for modeling an aircraft. Yeah!
Now I need to get all the information about the aircraft we purchase into this model. Well, once we order an aircraft. There are a few parameters that I'm not sure how to estimate. Does anyone have a good way of estimating the moments of inertia of an RC aircraft? Also, I could use some help modeling the engine (power consumption, torque, rotation speed, etc).
Once we have a simulation we can begin control law development. I am hoping to use modern control with full-state feedback. We'll see how that goes once we get there.
Another feature that Brian and I would like to implement is hardware-in-the-loop simulations using Simulink. However, I don't have the Simulink add-ons for the communication. Does anyone know of some free/inexpensive software that does this?
I should get back to my "real" job. As always, advice and feedback is greatly appreciated!