We've spent quite a bit of time considering the instrumentation of the vehicle -- what sort of data streams would be valuable and how we would use them. We decided a while ago to build an instrumented propeller hub but spent more time than we would have liked choosing, locating and matching the parts to make that happen.
Through the magic of Ebay we finally picked up 8 affordable load cells. These cells are not exactly what we needed for all locations, but we have the ability to mill them, modify them and make them work on our budget.
We'll radially place three of these cells near the front of the hub to measure prop thrust, two will be placed at the back of the hub to measure torque and down below we'll build two into the frame of the chassis to measure the resistive force being place on the wheels by the ground. From these three streams we'll be able to derive prop efficiency as well as overall power transmission efficiency.
We had to figure out how to get our data off our spinning prop hub. We preferred to have access to this data 'real time', rather than storing it on the hub for later download.
In our real business, we work with a Canadian RF design shop regularly- Pacific Design Engineering (http://www.pde.com/). They helped us locate an off the shelf RF solution that will do the trick and then they generously sent us a sample to use on the project.
THANKS PDE!!
We'll be programming and testing this telemetry system over the next few weeks.In the end, these are the data streams we plan to be logging on the vehicle:
propeller thrust
torque applied to prop hub
prop shaft speed
retardant force on drive wheels
drive wheel shaft speed
Additionally, we'll be measuring and logging GPS plots and relative wind direction and wind speed at three levels on the vehicle -- low, center and top of prop. We'll likely use digitally instrumented pitot tubes and will place these well in front of the vehicle and out of the region of prop influence.
