Wireless Acceleration Analysis on
Fully Actuated Drone
Background and Task
The chair of dynamics and mechanism design at technical University Dresden is operating a fully actuated drone. It features six rotors that are mounted in a certain angle to each other. Thus, the drone can be controlled in all six degrees of freedom (three translational, three rotational) without mechanically turning the rotors and therefore without tilting themselves. This allows for example to push against an object without rolling or pitching the drone.
In a research project, a vibration sensitive sensor must be mounted on top of the drone. Therefore, a vibration isolating mount was designed by the researchers. The task was to quantify the vibration reduction in operation using our in-house developed wireless acceleration sensors.
Here, we would like to show you a brief overview on the measurements and the results.
Setup and Methodology
Two wireless accelerometers were attached to the drone. One on the very top, replacing the vibration sensitive device and another one on the frame of the drone. Two measurement have been performed: one with and own without an additional mass on top of the drone to replicate the weight of the usually mounted sensitive sensor.
Using this approach, the drone can operate freely, all position controllers are active and creates a representative structure born sound level.
Measurement results and analysis
Overall
| RMS | load 30 grams | load 80 grams | ||
|---|---|---|---|---|
| [g] | Frame | Top | Frame | Top |
| X | 2.5 | 0.43 | 2.18 | 0.45 |
| Y | 1.43 | 0.31 | 1.50 | 0.36 |
| Y | 2.69 | 1.02 | 2.51 | 1.06 |
| SUM | 3.95 | 1.15 | 3.64 | 1.21 |
In average, a vibration reduction of about 10dB (factor 3) from the frame to the top mount is achieved due to the soft mounting structure. However, still an average level of +/-1g predominantly in the z-direction was observed during the flight maneuver.
Rotation speed and high Frequency Acceleration
To better understand the results, it is worth digging a bit deeper. Below are shown the acquired time signals and computed spectrograms (and corresponding time signals)
A brief harmonic analysis was done at the sensor of the frame in z-direction (30g load) when the drone was hovering at a constant position. The main excitation is visible at 284Hz up to 6 higher harmonics. However, there is more to examine, such as sub-harmonics (e.g. 350Hz and 457Hz). All of this can attributed to six motors rotating at similar (but not the same) speed with three rotor blades each.
Looking at a spectrogram, this becomes even more obvious. During the time 55s to 70s, the operator tilts the drone. This means, the rotation speed of some rotors needs to increase, while others need to decrease or remain constant.
Conclusions
Our unique, wireless accelerometers allowed to verify the reduction on vibration in operation between the frame of the drone and the sensor mount on top by around 10dB. In addition, from the measured signals, a characterization of the rotation speed of the rotors is possible. Feel free to contact us anytime, if you want to learn more about this topic.