IARC Progress Report – 3/12/11

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Spring break has been a welcome opportunity to make some progress towards the physical realization of the Emu. Yes, that’s what I’m naming the thing. And yes, I know emus don’t fly. But by setting the nomenclatural bar so low, I’ll hopefully come away from this experience pleased. Here’s a run down of everything I’ve accomplished in the past 2 weeks or so.

1) Physical Frame Realization

I had the top and bottom frames completed awhile ago, but adding in the vertical struts was the hardest part. Shaping quarter inch square balsa strips to mate perfectly with nylon bearings was a painstaking task, made slightly easier by the use of a dremel for cutting recesses. I had to make sure the bearings lined up so that a carbon fiber axle could fit in and lay horizontally, as well as ensuring constant clearance between the bottom of the frame and the top. This involved repeated applications of sandpaper and measuring.

2) Modularize Components

Last year the motors and ESCs were soldered directly together. In terms of weight minimzation, it was the best option. In terms of prototyping, it was a nightmare. I added some bare leads to the motor and speed controller, and I’m going to make an interface board/hub where I can plug everything in. This way, everything on the blimp will be theoretically replaceable. Unfortunately, with one of my 3 brushless motors broken, there is no plan B.

3) Melted a wire.

I think I connected a ground to a positive lead. Luckily this wire chose to burn first. The “weakest link” tipped me off that I screwed up before any other components or wires fried.

4) Endurance Testing

I ran a test with a single motor running at full power for over four minutes. The run time of the competition is approximately 2 minutes. Since I’m going to be running 2 motors plus a few lower-draw servos and a camera, a 500 mAh LiPo battery (the smallest and lightest I have) should suffice. I continued running one motor at 50% for another five minutes before the indicated voltage dropped below 6 volts so I have a little extra juice if needed. I may want to purchase another battery, however, so I can swap out packs between runs.

5) Wireless Testing

Using a numerical signal strength readout on my iPod, I was able to gauge the level of wireless interference being dished out by blimp components like the camera. Since almost all consumer electronics operate at 2.4 GHz, I was reasonably assured that disrupted Wi-Fi would also equal disrupted blimp communications.

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