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Monday, June 21, 2004
Armadillo Aerospace News: Good intentions, bad results
Armadillo Aerospace: If anyone missed the mid-week update I did about the perfect flight of the small vehicle, go read that first. We had problems trying to hover the big vehicle this weekend.
A minor improvement I have made to the laptop software is to display the dilution of precision (PDOP) number from the GPS on the status light, because previously it would have been green even if it was running with very poor coverage. I need to spend some time and collect more GPS diagnostic information, like satellite S/N ratios, but I’m not sure if I want to add a lot more traffic to the serial port during actual run times.
The first problem we ran into was installing the batteries in the new battery boxes on the big vehicle. We have started using upset thread lock nuts for a lot of things now, but when rapidly tightening them down on one of the battery clamp studs, it galled onto the stud. We use stainless for everything, because a little mist of peroxide will corrode steel bolts pretty badly, but galling is a common issue for us. Using anti-seize prevents this, but we should probably use nylon insert lock nuts in areas that aren’t going to be heat affected, and leave the all-metal locking nuts just for areas near the engine. We had to cut off the studs and weld new ones in place, all inside the vehicle, because the battery boxes are permanently bonded in.
When we rolled the vehicle outside, we noticed something off when I ran an extra check on the jet vane controllers: vane one was moving about half speed one direction, but full speed the other direction. We puzzled over this a bit, finding that swapping controllers around always had that actuator displaying the move-slow-one-way behavior, so we were confident it was the actuator. This was the new one that we had replaced after melting one of them last test. We were thinking that we could still test with a slow drive, because it was still moving fast enough to work, but while exercising it with normal flight movement, Phil looked over our way and let out a cry of “Smoke!” A pretty good quantity of smoke was coming out of the cabin where the electronics were mounted. One of the motor drives was fried. Fortunately, we have plenty of spares of the driver board, so we prepped up another one and replaced it. To make us even more confused, when we tested the problem actuator directly with a manual switch box, it was full speed both ways, and when we pulled the valve off and tested it with a different channel on the burned board, it also ran fine both directions. The new driver board still showed the slow-one-way problem, so we stopped quickly to avoid smoking it. We finally thought to check the resistance from the motor drive to the vehicle frame, and found that there was a low resistance path from one of the drive leads to the motor shaft, which makes its way to the vanes, conductive graphite bearings, up through the engine, and back to ground through the spark plug return line. None of the other valves were like this. Read More
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