Avinash Rao, a PhD student at the University of Canterbury, describes a rocket project to control the motion of a rocket. He and fellow student Malcolm Snowdon set out to develop technology to control the roll of a rocket. He demonstrates the parts of their rocket and how this roll control was achieved.
We were seeking to build a small rocket to develop some control theory around that – so to build a small rocket, to fly it, to demonstrate that we could control it. The four main components of our rocket design were the motor to provide the thrust, the air frame to make sure we fly nice and smoothly, the avionics to control our trajectory and the recovery system to make sure we get the rocket back.
Malcolm’s role was the air frame and the propulsion. So he built the rocket motor, he did all the static testing, he designed the air frame and machined parts of it himself and had other parts machined here at the university. I was more involved with the actuation and the control avionics, so building the electronics to control the rocket, coding up the electronics and also the actuation, so how to move the fins, the server motors and things.
In the end, we decided to just try and control the roll, which is the roll about the axis of the rocket as it’s flying upwards. First of all, we have a sensor, the gyro, and as the rocket spins, that puts out a voltage which is proportional to the rate of spin. So then it knows, OK, that 5 volts means that we are spinning at 5 degrees per second, for example, and then it puts that through an equation which says, OK, if we are spinning at 5 degrees per second, then how much should we actuate the fins? It does that and then it spits out the result to another control board, which then says, right, we need our fins to go to 5 degrees. That will then decide where to put the servos to get to 5 degrees.
So there is a whole sort of chain of things which it goes through from the sensor through to the processing through to the actual actuation of the fins in order to correct that roll and get us back on target. The rocket was pretty successful overall. We got up to a height of about 600 meters, and we did manage to demonstrate roll control.
University of Canterbury