I am working on a medical drone project as a mechanical design engineer. The primary objective of a project is to deliver blood and essential medical supplies from well facilitated zones to health posts of rural zones using drones. To fulfill that objective, we first have to fulfill different technical objectives like long range of drones, launching and landing of drones, delivery system for blood and medicinal supplies, drone control systems, modularity of drones, reliability and safety of drones, efficiency of drones, etc. Since our objective requires long range, fixed wing drones are used in our project.
Let’s start the journey with my first task in the project. My first task was to design a launcher for a fixed wing drone. Before, a drone was launched from hands and to make the launching process easy, repeatable and automatic, a launcher was required. Before designing anything, one must find out what are the requirements for design. So, as a design requirements, I collected some points like the designed launcher must launch the given weight of done (5 kg) at 25 m/s, the designed launcher should be as small and portable as possible, the designed launcher should be modular and can be assembled or disassembled easily, the designed launcher should be able to operate in both manual and automatic mode, etc.
To operate manually, the elastic bands are to be used while to operate automatically, a highly powerful motor is to be used. So, taking all the design parameters into consideration, first of all the motor was selected for the launcher considering some level of safety factor. Then the conceptual design of the launcher was built in Solidworks. Solidworks is a tool to make CAD (Computer Aided Drawing) models. Using a Solidworks, different concepts are built, analyzed and then accepted or rejected. Also, CAD was used to do stress analysis and assume a level of vibration created on the launcher. Sizes and materials are selected from those analyses. Then bearings are selected according to the load it has to bear using some calculations. Instead of directly going through fabrication of the launcher, the building of CAD models helps to know the problems faced during fabrication and solve them beforehand, to check if what we are building is what we want, to know the behavior of design, to minimize the cost, etc. Once the design has been finalized, the workshop drawing showing all dimensions, views, names and number of parts to be manufactured is built and then the Bill of Material (BOM) is made. BOM is the list of materials showing their required quantity, their cost and overall project cost estimation. Then the workshop drawing and CAD model was sent for fabrication.
Then my second task was to design and fabricate a payload dropping system. The design requirements for the payload dropping system were that maximum two micro servo motors could be used as an actuator, the payload dropping system must take small space so as to maximize the size of payload box while space available for payload box and payload dropping system inside drone was already known, the payload dropping system must be lightweight, the dropping system must be reliable and repeatable, etc. Then I divided the design of the payload dropping system into three different parts i.e. payload box, payload locking mechanism and door opening mechanism. A payload is supposed to be placed inside the payload box. Payload locking mechanism has to lock the payload box on the drone and unlock it to drop the payload box. Door opening mechanism has to open a door from the drone to drop the payload and then close the door once the payload is dropped. One important thing to be noted is that the payload box doesn’t get any support from the door. The purpose of the door is only to stop the airflow inside the drone. If the door is not closed, more drag is created that decreases the flight time of the drone.
After thinking and searching for some time, the payload locking mechanism was designed that works like a door lock. The lock is locked and unlocked using a micro servo motor. Then the
design was 3D-printed, laser cut, assembled, tested, modified the design and repeated the process until we get the perfect result. Then linkage was used to make a door opening mechanism. To make a perfect door opening mechanism as our requirement, ‘Linkage’ software was used. Once the lengths and sizes of all the linkage are finalized, it was designed in Solidworks, laser cut, assembled and tested. The door opening mechanism also uses a micro servo motor as an actuator. Then the locking mechanism and door opening mechanism were fitted inside the drone. Measuring the remaining space for payload, payload box was designed and fabricated. Then, the final testing of the overall system was done and it worked perfectly.
My next task was to do research on carbon fiber manufacturing. Currently, drones were being manufactured from plywood, Styrofoam and carbon fiber tubes. First I calculated how much weight we can reduce when we use full body carbon fiber. The result was that we can reduce a lot of weight from the fuselage (body of drone) when we manufacture it from carbon fiber but the weight of the wing would be increased when we manufacture it from carbon fiber. We calculated the weight taking the volume from CAD design and multiplied it by density. I also did quite a research on different types of carbon fiber manufacturing, layering techniques and calculated the strength of carbon fiber in different directions according to layering.
Then my next task was to design a structure for the wing and fuselage for a new drone. The aerodynamic design was already designed by a friend. I had to design a structure according to that design and make sure the drone is strong and reliable enough to take flight and easy to manufacture. First, different structures were designed for the wing and the structures were simulated in ‘Ansys’ for stress analysis to know stress at different places and total deformation on the structure. For stress analysis, the uniform load of total weight of drone with certain factor of safety was applied along the wing. We needed the deformation of structure to be minimum. The sizes of spars are also chosen according to the stress analysis. Then the structure for the fuselage was selected using the stress analysis considering the stress given by weight of battery, thrust given by motor and propeller, etc. and doing some impact tests. For impact test, impact on structure of drone due to small crash was analyzed.
Searching and trying for new things to solve certain problems is quite fun. Every time I work as an engineer in this project, I really feel proud to be part of such a novel project. It is very fun to be around innovative ideas and work on an innovation field. You always get to think differently and nurture your brain and skills. Also, watching your ideas, works and skills being used to solve problems really overwhelms your heart. Instead of doing some repetitive work, doing research where you face new challenges everyday and the excitement of overcoming those challenges makes the work very adventurous.