July 21, Tuesday

In fluid dynamics, a drag coefficient is a dimensionless quantity that is used to quantify the drag or resistance of an object in a fluid environment. The higher the drag coefficient, the higher the drag the object experiences. In order to minimise the drag on our blimp, an ellipsoidal shape seemed to be the best option. Most commercial blimps like the Goodyear airship adopt this configuration, and we saw a few other homemade blimps that are also ellipsoids with sharp noses and tails.

For the first balloon, we made a rough ellipsoidal version of the actual size (110cm x 40cm) and double-sealed them by ironing the Mylar pieces together. Tears were repaired to the best of our abilities with tape. We inflated the balloon multiple times due the presence of new leaks every time we filled it up. As such, we decided to try folding the excess edges of the balloon and iron them together to strengthen the sides.

 

After countless agonising attempts to repair the leaks, it was obvious that we were fighting a losing battle and heat sealing was not the way to go. Though it is indeed a quick and easy method, troubleshooting the end product proved more trouble than what its worth.

July 23, Thursday

Most of the components that we have ordered have arrived and we started to test them out to ensure they are in working condition. As the Arduino IDE was not working and our RC set has not arrived, we could not test out the servos. However, we were able to test out our coreless motor and propeller.

 

To our dismay, many parts that were supposed to be connected together did not have matching connectors, such as the battery to the ESC. The ESC did not even come with connectors to the motors! After much soldering and frustration at reading the RC manual, we successfully connected our servos and ESC with coreless motor to the receiver, and the battery to the ESC. We were also able to control them with our RC. Channel 3 of the 9X RC was reserved for throttle (coreless motor) while the rest were suitable for servos only. After which, we had an unofficial project update with Dr Ho on what we have accomplished so far, and the technical skills that we picked up along the way.

 

 

We also had to consider the direction of the propeller and motor after Kanesh pointed out that there are “pull” and “push” propellers, which are made with a counter-clockwise propeller and a clockwise motor, or vice versa. 

 

After we were done with the motors, we tested out our wireless video transmitter and receiver too and they were able to work on 4 different channels. We settled on a 5.725GHz frequency which was indicated by a blue-white flash from the transmitter. Though there was a bit of static when the camera was brought further away from the receiver, the graphics were decent with a 150 degree field of view.

 

Although the batteries for the main circuit and camera could be charged via a tabletop power supply (4.2V, 1.0A), we had to solder an adaptor piece to the battery wires in order to charge them with a LiPo battery charger if we ever have to. It is important to note that if the battery is not be in use for a long time, we have to discharge it to its storage voltage of 3.7V to prevent it from getting damaged.