September 24, Thursday

Preparations for avionics of V3 were almost complete. We also requested for Kanesh to come down and supervise our progress.

Both speakers were tested in the MNT lab – 1 member was holding the speaker and the other holding the microphone, both standing at opposite ends of the lab. Though the smaller one was more lightweight (36g), its sound quality was poor. Instructions relayed were extremely muffled could not be deciphered. We ultimately settled on the bigger one (96g) since our balloon could support its weight anyways and it provided excellent sound quality.

 

As tested before, the seams were more than capable of supporting 25g each. We  carefully punched 4 holes using a hole puncher – 2 on each side along the seams – to not puncture the balloon itself. The first pair was located near the front while the 2nd pair was located close and slightly behind the CG. 1 string was strung through each pair and both strings were used to hold up the speaker, thus distributing its weight over 4 holes. By adjusting the length of each string, we were able to adjust the position of the speaker between the first pair and second pair of holes.

After doing moment-balancing, we flew our blimp again. However, the blimp was veering to the right when we did not touch the yaw control – it was unable to perform straight flight. Since we have eliminated the torque factor, it is plausible that we did not align the propeller well along the centre line and its line of action does not align with that of the balloon.

 

Furthermore, pitching did not seem effective at all. Initially, we thought it was the addition of the large mass of the speaker that hindered pitching. However, this could not be the case since the balloon was lifting almost similar masses for both flights. In the initial flights without the speaker, blue-tack was used as counterweights to ensure buoyancy. In the flights with the speaker, blue-tack was also used to ensure buoyancy. Hence, weight is not the issue since the propellers are pushing a blimp carrying similar mass but rather, the distribution of weight.  The larger mass of the speaker meant a larger moment about the CG at the front half of the blimp.  When the propellers are pitched down to push the blimp up, the blimp has a negative angle of attack (AOA) and its nose points downwards instantaneously. This is due to the large anti-clockwise moment of the speaker which is also increased by the propellers pitching down.  The blimp with speaker is much more stable in negative AOA since the clockwise moment from individual avionics and small masses of blue-tack are very small. Propellers that are pitched down in this stable negative AOA position are angled closer to the horizon.  Thus, the vertical vector of thrust is much lower and pitching motion of the blimp as a whole is not effective. As compared to the blimp without speaker, the masses are much more evenly distributed. Hence, it is not not as stable in negative AOA, allowing it to rotate back quickly and provide a large vertical vector of thrust.

Here is an overview of Kanesh’s critics and suggestions:

1. Unable to achieve straight flight – not much suggestions apart from realigning the propellers
2. Unstable propeller holder (wobbling and vibrating) due to abrupt, jerky servo motions – redesign a more sturdy propeller holder
3. Loose servo arms and prone to falling off – screw the arms to the servo motor
4. Servos were connected weakly to the propeller holder with tape – redesign 3D connection parts to accommodate the servos