Propulsion Mechanism

Our inspiration came from the previous year’s HoverFish project, and we wanted to build a balloon that could improve on the flaws that they had. Their fish was unable to travel in a straight line due its fin-flapping mechanism and it was slow in terms of moving and turning. Hence, we wanted to build a balloon that is faster, more maneuverable and equally compact.

 

 

We were inspired by the biomechanics of a squid and came up with our preliminary ideation.

We settled on a similar flapping propulsion mechanism as the HoverFish​. However, instead of a single fin, we want to replace it with 6 legs​ with 3 on each side. They will be made with a large piece of lightweight material between them to control the yaw​ as well. We also wanted to employ elevators instead of a bladder to control the pitch​.

Leg Design

2 main designs were simulated to determine structural integrity​. The one on the right was chosen as it managed to produce more force in a rudimentary test that we carried out.

Optimization

Axles were used to pass on the rotational energy from the servo to the legs. A universal joint was chosen for rotation on different planes​. Although it was heavy (~40g), the 2nd iteration (middle) was chosen​. We conducted an experiment to deduce the amount of forward thrust produced by 1 set of legs, which was found to be  produced 0.186N (19g). This meant that around 0.372N of forward thrust will be generated from both sets of legs.

Leg Attachments

From a flapping dynamics research paper that we found, factors for a higher lift include:

  1. Low thickness,
  2. High flapping motion frequency
  3. Redundancy for swept wings
  4. High amplitude of motion

These factors were then considered before we dived deeper into designing the flaps to be attached on the legs.

Pitching Mechanism

At lower speeds, an elevator is likely to slow down the balloon’s movement due to its increasing overall surface area when deployed. Hence, we decided to use the bladder mechanism instead.

Test Balloons

Shape: Circular
Dimemsions: 20cm x 20cm
Number of Mylar pieces: 2
Seal: Double-sealed with iron

 

Shape: Ellipsoidal
Dimemsions: 110cm x 40cm
Number of Mylar pieces: 2
Seal: Double-sealed with iron