July 7, Tuesday

We went for a drone simulation training conducted by Kanesh, a mentor who helped us in the deciding the technical aspects of our blimp. While the training simulates an outdoor setting, the remote-control handling skills we learnt are applicable to help us in flying our blimp indoors too.

 

After much deliberation since week 2, we decided to change the propulsion method from the flapping of legs to a single propeller. While performing a free body analysis, we discovered that the legs that were designed to be attached to the back of the balloon were heavier (46.6g) than the bladder mechanism (39g). This is forecasted as a problem for pitching of the blimp since it is back-heavy. Additionally, it is also much easier to maneuver the blimp by controlling the direction of the propeller which provides a consistent thrust instead of “pulses” of thrust provided by the legs. Kanesh kindly passed us a whole box of motor and propeller components, which sparked the idea of using coreless motors.

July 8, Wednesday

“A deadline is negative inspiration. Still, it’s better than no inspiration at all.” – Rita Mae Brown

We held an all-day MS Teams meeting to research on electrical components and circuit design (the links to some of the resources we used are provided at the bottom of this page). In the initial design, we wanted to use servos to control the legs as we were apprehensive of the weight of a DC or brushless motor. After Kanesh introduced us to coreless motors, we realised that they are one of the lightest motors we could get our hands on. They are mainly used for mini-quadcopters. This further cemented our decision to switch to propellers instead.

The circuit is split into a main circuit (motors, servos) powered by a main battery and a sub-circuit for the camera, which was powered by a sub-battery. This design was recommended by Kanesh due to safety reasons. The 6.5cm propeller and motor (8.5x20mm, 53500RPM) were picked based on what were recommended together by the supplier. SG90 servos to control the bladder mechanism and yawing were chosen due to their levity (9g). We then decided on a 9X Turnigy remote control (RC) that was highly recommended by Kanesh too. The use of the RC allowed us to scrap our programming since the joysticks on the RC can move the servos and power the motor.

After scrutinising a few Do-It-Yourself drone guides, we understood that we were unable to connect the motor directly to the RC’s receiver of the RC unlike the servos. An electronic speed controller (ESC) had to be integrated into the circuit. This wrapped up the list of components to be added into the main circuit.

 

 

Choosing the right lithium polymer (LiPo) battery proved another challenge.  Properties of a LiPo battery are described by XXS (number of cells in series) and XX capacity. A short visual is presented above. The dangers of LiPo were made well-aware to us during our drone briefing. As circuit design was extremely foreign to all of us, we visited many websites to get started. Operating voltages and working voltages of each component were all taken into considerations and we narrowed the choices down to either a 1S (3.7V) or 2S (7.4V) LiPo battery. These voltages are the nearest to the working voltage range of the SG90 servos (3.5V – 6V, operating voltage: 4.8V). Though we were leaning towards the 1S LiPo, we decided to consult Kanesh first before making any uninformed confirmations.

 

July 9, Thursday (1st Progress Meeting)

During the 1st progress meeting, we presented our initial plan, proposed our new propulsion mechanism (and the rationale for abandoning the old one), circuit design, and struggles with circuitry and balloon construction to Dr Ho and Kanesh. They gave us valuable advice on how to move on from there, such as the types of electrical components to look out for, and how to better seal the Mylar pieces together using the double seal technique.

 

This simple technique requires an additional fold in the seams in case the first seam is imperfect which can result in micro leaks.

Kanesh also taught us a method to calculate the thrust for the legs’ flapping in the event where we decide to use the old propulsion mechanism (we eventually tried it out in week 7). After the meeting, we also managed to confidently choose a 1S 2000mAh LiPo as the main battery and a 1S 200mAh LiPo as the sub-battery. Finally, our components list was confirmed and we proceeded to order. The ESC was an unexpected component that added another 5g, which pushed the total component mass to almost 100g. As such, we had to start making considerations for a much larger balloon that can lift a payload of 100g.

 

Referenced Materials:

How to Choose a Lipo Battery For RC

https://www.build-electronic-circuits.com/circuit-design-from-scratch/

The Battery Eliminator Circuit

https://power-calculation.com/battery-storage-calculator.php