Propeller - Motor matching (featuring Maxon)
For every UAV, a highly efficient propulsion system is crucial for its success. Efficient combination of electric motor and propeller effects the power consumption which is directly translated into flight time. The only way, to significantly increase flight time is to carefully match the propulsion system. How do we make sure that our propeller perfectly fits the used motor?
The answer is quite simple. The match of motor and propeller must be made correctly. But what are the key points to be considered? The overall efficiency even with super effective motor but in combination with an inappropriate propeller does not fill out its potential. Creating a highly effective setup requires the efficiency performance map of the motor as well as the efficiency of the propeller at operating area for the UAV to be known.
To create the efficiency performance map of the motor, the motor response to different loads over a wide RPM range must be measured. The efficiency of the motor is then calculated from ratio of mechanical (shaft) and electrical power.
According to the resulting efficiency performance map the propeller performance can be adjusted to the area where the motor is most efficient and propulsion system still fulfills the requirements of the overall system. The efficiency of a propeller described by Figure of Merit, which is calculated from power and thrust coefficients, is also included in simulation to estimate the overall efficiency of the propulsion system setup.
All these steps can be performed by our team to provide optimized high-effective propulsion system to our customers.
To show the whole optimization procedure one example is presented.
1. The motor efficiency performance map
As already mentioned, the motor performance map is very important for the process of optimizing a propulsion system. In this case the sophisticated performance map was created by our Swiss partner Maxon. As competent partner for high-precision drives and motion control maxon has deep knowledge and experience both in motor design and simulation. They were able to simulate the motor behavior beforehand to find the optimum between performance and efficiency. The below shown efficiency maps of the motor was the baseline for an optimized propeller design. This accurate performance map allowed us to move the optimization process to a next level. The red points represent the original (off the shelf) propeller used on this motor at different thrust levels. It is obvious that the efficiency of the motor is not highest in this region.
2. Customized propeller
Therefore, the simulation of customized propeller was made to increase overall efficiency of the propulsion setup (to utilize more effective region of the motor performance map). This would require to shift the characteristic propeller line more towards the bright spots of the motor efficiency map.
3. Testing of optimized propulsion system
Based on simulations the design of the propeller was created and the propeller was manufactured. The whole setup was tested, and the results were compared to simulated data. The accuracy of simulation (torque x RPM) is very high so the propeller operates in higher efficiency area of the motor as desired.
The result of optimization process is a more effective propulsion system (with lower electrical power consumption) which still meets the requirements of the UAV.
The optimized high-effective propulsion setup is the key to get farther.
Radovan
