August 3, Monday

In order to make a balloon with a larger volume (around 5x larger to achieve ~0.981N/100g of lift) without increasing the length and width of the balloon too drastically, we decided to seal 3 pieces of Mylar instead of 2. This technique was inspired by a hobby blimp maker with a lot of experience in Mylar balloon construction.

 

 

The dimensions of the stencil were larger at 180cm by 106cm, and they include the 5cm margin for the contact adhesive this time due to an oversight by us (i.e. the actual size of the 1 sheet is at 170cm by 96cm). 

A size upgrade

Similar to our previous balloon, this balloon was also double sealed with contact adhesive. However, the process was much more tedious than before as there were more sides to seal. Also, we discovered that sponges were effective substitutes for brushes too. 

 

Sponges are ergonomical brushes

While waiting for the adhesive to dry, we tested out the thrust generated from the initial squid propulsion legs we had in mind before the propeller. 

 

Measuring thrust with a weighing machine

 

 

3 legs were able to generate a thrust of 0.186N (19g) and hence 0.373N (38g) of thrust for 6 legs.

Thrust testing for 1 propeller was done in a similar fashion, with it being taped down to a weight placed in the centre of the weighing machine. 1 propeller was able to generate a thrust of 12g. Although it is lesser than that of 1 pair of squid legs, using the propeller is much more lightweight and it also gives us the freedom to shift it around for moment-balancing. At this point, we have decided to abandon the legs design completely and move on solely with propellers in mind.

August 6, Thursday

During our 2nd progress meeting, we went through our project’s concept and the design and physics behind our blimp. Pertaining to calculating the moments about the blimp’s CG, Dr Ho gave us some advice where he suggested using dummy weights to represent the different electrical components on the blimp and attach them along the edge with blue tack.

We also spoke to Kanesh about the difficulty in calculating the volume of helium in the balloon as using the formula of the volume of an ellipsoid or a prism is likely to be inaccurate. He suggested placing one ellipse piece of the Mylar on a Cartesian plane and record the coordinates of the curve of the ellipse. These values can then be used to create a rough 3D sketch of our balloon on a CAD software, which will then able to give us the volume of our shape. We subsequently carried out his suggestions and the results are further elaborated under Week 12.