Design, fabrication and evaluation of a 3D printed thrust sensor for application in drones

Recently, additive manufacturing, best known from 3D printing, has become a common method for fabricating a wide range of sensors. With 3D printing, sensors can now be fabricated with sufficient surface finish and accuracy. Furthermore, it is now possible to fabricate entire sensors or by embedding the sensor into printed structures.

This master thesis assignment deals with the design and fabrication of a 3D printed thrust sensor to be implemented on drones. Amongst other things, this approach of integrated sensors in standard structures of the drone by the use of 3D printing provides the flexibility to upgrade sensor designs easily so as to meet varying and customised requirements.

In this assignment, the lift force of a rotating propeller was first analysed considering two scenarios: blade flapping and drone arm deflection. The two scenarios were analysed using Finite Element Method (FEM) simulations and several factors were taken into account: implementation of the sensor, effect of additional weight, ease of 3D printing and so on. Based on the comparison between the two, it was deemed suitable to compute thrust by measuring the deflection of the drone arm.

The first part of the assignment deals with the design and fabrication of the sensor using two materials: Polylactic Acid (PLA) and Conductive PLA. With the help of FEM analysis, stress and strain distribution is analyzed on the drone arm to find an optimal position for sensor placement. Using a linear actuator, the sensor is then characterised to determine non-linearity, drift , hysteresis and repeatability. The results from characterisation are then validated using a motor setup.

The second part of the assignment incorporates the estimated deflection to develop a control architecture made of a sensor-based feedback channel, taking into account several factors such as hysteresis, drift, and non-linearity as exhibited by the sensor. The controller is then tested under the influence of ground effects. It was observed that the controller is able to compensate for the extra thrust generated due to the ground effect.

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