A lot of thought goes into designing an efficient flying vehicle - if you've ever seen flaps on a passenger jet's wings, you'll have some idea of how many parts are involved in keeping a plane stable.
On a UAV, the same principles apply on a smaller scale. If the UAV encounters a gust of wind (turbulence") or needs to manoeuvre quickly, there needs to be stabilisation to prevent the disturbance from overwhelming the UAV. This is where practical testing for the motor/propeller combination is useful for obtaining actual flight characteristics so that the vehicle design can be improved.
We've made use of these characteristics during our R&D process and enlisted the help of our masters student, Zachary, to design and build this test rig. It features a gimbal-like mechanism to transmit the forces produced by the propeller and wind tunnel along the two axes, a variable force transducer location to utilise the full capacity of the load cell regardless of the electric motor/propeller combination used, and a universal motor mount to permit the mounting of various types and sizes of electric motors. The test rig also rotates on a stand to allow for testing of the propellers at multiple angles of attack (if mounted inside wind tunnel).
On the primary axis is a subminiature load button load cell with a capacity of 111N (11kg) and this measures forces produced directly by the propeller. The secondary axis has a load cell with a capacity of 44.5N (4.5kg) and it measures the reactionary torque and lesser forces produced by drag of the test rig within the wind tunnel. The signals measured by the load cells are amplified on the data acquisition board and passed to the flight computer to be processed.
The entire test rig was manufactured in-house from aluminium, along with 2 key shafts in steel for greater stiffness. The data acquisition board was also manufactured in-house.
Results from this test rig can come from various combinations of fan speed and angles of attack, depending on the desired operating conditions.
Thrust is the primary data obtained from these tests - it directly measures how efficient this motor and propeller combination is.
Reactionary torque, as mentioned earlier, requires a secondary transducer in the perpendicular axis in order to measure it - this also means it can't be calculated analytically easily, which is why testing is crucial.
Impulse testing can also be performed - this determines how long it takes a given signal to reach a stable level, which affects the control systems design of the UAV.
Are you designing your own UAV and would like real performance data for your chosen components? We can test motor/propeller combinations from anywhere - we can obtain the parts or if you prefer, send the components to us. To download a sample file of the data obtained from this testing, click here.