Because the propeller is spinning, we chose to use a radio link to send its data to a computer on the cart’s chassis to be logged in real-time. We found a very slick device made by Texas Instruments. The EZ430-RF2500 includes two integrated devices that include a microprocessor, radio, and data acquisition capabilities. Unfortunately, no one on the team knows how to design low-level circuits or program such devices. However, there’s no better opportunity to learn.
With a fair amount of help from friends, we’ve muddled our way through to developing a prototype circuit to read and amplify the output of a load-cell, and get it into the 430. With more help from friends, we figured out how to program both ends of the 430 to read the signals from the load-cells, transmit them to the chassis, read them on the other end, and stream them into the laptop to be logged (and displayed to the pilot). Finally, we had to figure out how to read a serial stream in Windows since they no longer make laptops with serial ports and my old DOS serial routines can’t talk to a USB serial converter.
Having gotten this far, we’re feeling good about our ability to collect the data we need – not just for “the event”, but also for testing component performance (e.g. transmission, rolling resistance, propeller torque and thrust…). This will allow us to optimize the prop pitch, gear ratio, and other parameters before we attempt actual trials.
Fortunately, one of our friends that we met on the internet forums (Christian Klippel) has designed a really slick circuit and PC board to replace the prototype circuit we’ve cobbled up for proof of concept. We’ll be sending that out for fabrication in the next day or so. That should cover our instrumentation of the propeller. This will give us thrust, torque, and prop-pitch at all times.
Next comes the instrumentation on the chassis. Again we’ll use the 430 to collect load-cell data (for things like the force on the drive axle), but will need to develop a new bag of tricks for measuring things like prop RPM, wind speed, and wind direction. More on this as it develops.
