Airserve is an Indian start-up based in Hyderabad which uses sophisticated drones for aerial surveys and data analytics for various industries, such as construction, mining, and agriculture. Airserve approached T Works through the Product Design Services (PDS) channel with the task of designing a payload container that could attach on to their custom multi-rotor drone which can fly autonomously from one set waypoint to another. The container would be designed to carry essential medical supplies, such as blood and other body fluid samples, vaccines, or even anti-venom, from a periphery medical hub to near-by locations that may be difficult to access by road.
FASTER MEDICATION THROUGH INNOVATION - DESIGN REQUIREMENTS
There were several design requirements for this payload that made the product design an interesting engineering challenge. The major requirements were:
The volume of the container should be sufficient to carry 100 standard vials. The maximum weight of the cargo was capped at 1 kilogram. Since the total weight of the payload directly affects the flight time, the weight of the container had to be minimised to improve efficiency.
Many medical samples and supplies have to be stored at low temperatures (typically in the range of 2-8℃). Therefore, the container should thermally insulate the items for the duration of the flight to the destination (30 minutes).
The payload should be easy to attach to the drone underbody, it must remain securely fastened for the duration of the flight, and should be able to automatically detach via remote trigger once it reaches its destination.
FORM EXPLORATION
The dimensions of the container was constrained by the space available under the drone. The form is the shape of payload container of the and is an important aspect of any product’s industrial design. Our designer prepared several form choices for Airserve to choose from. Some forms emphasized aesthetics while others were optimised to reduce aerodynamic drag. Some form options are presented below.
Form exploration for the payload. The client and the design team collectively chose the top-left most form as the best suited for the drone.
MECHANICAL DESIGN
After a form was chosen, the engineering team considered the use of several materials and manufacturing techniques to realise the form. The production quantity is generally the main driving factor in choosing the best suited material and manufacturing process for it. Some techniques, such as injection moulding with plastics or metals, are only economically feasible when the production quantity is in the thousands, whereas we were looking to make a few sample payloads and the production run would be likely less than a hundred. Hence, we limited our selection to low volume prototyping methods.
We initially considered machining the entire container out of a slab of plastic but that would been both expensive and wasteful. Instead, we chose to fabricate the enclosure out of aluminium sheet metal as it was more economically viable, lightweight, and durable while being able to maintain the chosen form. The individual sheets were riveted together for easy assembly. The door is machined out of HDPE plastic. The payload mount is 3D printed out of ABS as it is lightweight and resistant to deformation at temperatures up to 90℃.
Final CAD model of the assembly
One drawback of using aluminium in this application is that it is a great thermal conductor and would quickly transfer heat from the hot ambient air to the cargo. In order to insulate the enclosure and its content, we added a thick layer of phenolic foam, which is an excellent thermal insulator. The door also has a rubber seal to ensure the container is airtight, preventing convective heat transfer with the ambient. We tested the device with cooled vials and the insulation was sufficient to maintain the storage temperature for the duration of the flight.
The assembled aluminium sheet metal enclosure (left) and the phenolic foam insulation (right) with a black 3D printed inner lining
TESTING
During the design phase, we evaluated two options for maintaining the storage temperature of the samples - active refrigeration and passive insulation. Active refrigeration involves the use of an cooling element such as a Peltier cooler. However, such devices are very inefficient and power hungry. Since they would have to run off the drone battery, they would dramatically reduce the flight time. Passive insulation, on the other hand, does not require any electrical power and relies on the use of materials with a low coefficient of thermal conductivity. Low density is also another insulator requirement to reduce overall payload weight. An air gap would have been the ideal insulator as it would be practically weightless but such an air-gap would have to be perfectly hermetically sealed to be effective, which would add a lot of complexity and cost to the design. Instead we used phenolic foam, which is also an excellent insulator and relatively light. We tested the device with cooled vials and the insulation was sufficient to maintain the storage temperature for the duration of the flight.
The payload with 50 vials cooled to a temperature of 4℃. The foam insulation and airtight seal minimises heat transfer to the vials from the external environment, restricting the temperature increase to just a few degrees over the flight duration.
Finally, we designed a novel detachment mechanism that can be remotely triggered to drop the payload once the drone reached its destination. Existing drone payload detachment solutions use a pin which is linearly actuated to detach the payload. This mechanism would not allow a user to easily reattach the box to the drone. Instead we designed a latch mechanism that is actuated by a cam and servo motor. This mechanism makes it easy for any user to easily fasten the payload securely to the drone. A combination lock was added to the door of the device as an added layer of security so that only the authorised personnel can access the sensitive contents inside.
The cam and latch release mechanism
Testing the release mechanism with a frame
Testing the release mechanism on the drone. Works like a charm!
Airserve has started flight testing the payload on its drones and is expected to begin demonstrating its services to interested stakeholders soon. Have a look at their demonstration video on LinkedIn. We at T Works are excited to see our design take to the skies and hope to see it used to expedite critical tasks for hospitals, diagnostic labs, and public healthcare centres.
