Propulsion

After an in-depth dive, we found an alternative to DC motors: coreless motors! Coreless motors are one of the most lightweight motors that usually found in mini quadcopters. Our propulsion method was unanimously changed to propellers as the squid legs were comparably heavy to propellers and offered no clear advantage. With the propeller, continuous thrust can be achieved. Besides, the bladder mechanism was barely able to counter the weight of propulsion legs. This would definitely lead to issues when trying to pitch down since a moment due to the bladder may not be attainable.

We settled on replacing the propulsion legs with one propeller​. The lightweight coreless motor with propeller has roughly the same weight as that of propulsion legs​. We would also be able to place it at the bottom of the balloon instead of at the back, allowing bladder mechanism to be better positioned​.

When using DC and coreless motors, an electronic speed controller (ESC) is required. We chose a 6.5cm propeller as it was the recommended propeller for our coreless motor. By securing it down to a heavy block on a weighing scale and positioning it perpendicular to the ground, we obtained an experimental thrust of 0.118N(12 grams). 

Avionics

We decided to use a 9X Turnigy remote control to steer our balloon due to its reliability and easy use of controls. 3 channels were employed for throttle, pitching and yawing respectively. After reading up on LiPo batteries, we decided to use a 1S battery with a 1200mAh capacity to lengthen our flight duration (31.1min). We had separate batteries for the motors and camera due to safety considerations. It would be dangerous for the camera to power down before or at the same time as the motor as that would mean the pilot would be flying without visual cues. Hence, a main 1S battery and a 1S sub-battery with 200mAh capacity with a greater working duration (60min) would be necessary even though it adds on to the weight of our blimp.

By referencing to some drone schematics, we figured out that the main 1S battery must be connected to the ESC and before connecting to the coreless motor and the receiver. Servos for yawing of the propeller and bladder mechanism will be connected to the receiver.

Balloon

Shape: Ellipsoidal
Dimemsions: 130cm x 50cm
Number of Mylar pieces: 2
Seal: Double-sealed with contact adhesive
Lift: 0.206N (21 grams)

The balloon was too small to lift up our electrical components, which was projected to weigh ~130 grams. As such, we had to design a larger balloon.