New Project: Wind Tunnel

It will be about 900mm long, 300 high and 300 wide.  It will be constructed from perspex and pine beams.

The fan and speed controller have already been completed (that was today's job, see below).

I will be using an idea I saw on a tv advertisement (one aimed at encouraging people into a career in high school teaching) in which a teacher had constructed a wind tunnel for his classroom.  He had used drinking straws and other simple and cheap parts to affectively make a fully functional model.

I will also be using some car washing sponges to baffle the incoming and outgoing air in order to decouple the rotating fan blades from the linear air flow.  I have found a beefy 12V, 1Amp case fan from a scrap computer.  I am controlling it using a simple, low-part-count circuit which uses a microcontroller to read a rotary potentiometer and drive a power MOSFET using PWM to regulate the speed of the fan.  This works very well and gives good, granular control of the motor speed.

I hope to make this wind tunnel interesting in one respect.  I will be able to up-end the entire thing and do vertical (in opposition to gravity) drag tests for evaluating paper parachute designs!  This might prove difficult but it should be fun finding out.

Here's a couple of pics of the speed controller circuit... (the source code for the ATTiny85 microcontroller can be found here).

The fan connects to the 4 pin header.  The unit requires a 12V PSU such as a wall wart or a laptop power brick.  I can upgrade this design to add a second fan if I decide that a single fan isn't up to the job.

The ATTiny85 is a fantastic chip for small simple projects like this.  I could have done this with a 555 timer of course but I like having the flexibility of the ATTiny85 which gives the potential to add automation features such as soft-starting the fans or setting thresholds on the max/min speeds allowed.

I'll be building the rest of this project this week and I'll put more pics and videos up here soon.

Stay tuned.