Archive for November, 2014
After many years, it finally consumed all the batteries in the apartment, so it was time to fix it.
The label of screw threads was removed forever. It only looked neat, but was never used.
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The label of screw threads was removed forever. It only looked neat, but was never used.
...Continue Reading
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The decision was made to convert contact lens agitator #2 to a traditional levitator, since so much work went into it. Would find a cheap thing to hang from it. Instead of reusing the existing electronics, would make a simpler circuit using knowledge gained over 9 years to do a better job. The original circuit had a full H bridge. The new circuit would just pull.
Opening it after 9 years revealed a few critters. It was indeed a steaming pile of dog turd. It was a miracle the original circuit ever worked at all, since it didn't use star grounding, relied on a dog slow LM324, had a lot of unnecessary parts for what seemed to be lowpass filtering. It relied on extreme capacitance to work around the grounding. It was the product of many experiments without an oscilloscope.
The 1st attempt used a MOSFET with full belt & braces snubber diodes. It quickly overheated & destroyed itself. It went back to a tried & true BJT with no snubber diodes.
...Continue Reading
Opening it after 9 years revealed a few critters. It was indeed a steaming pile of dog turd. It was a miracle the original circuit ever worked at all, since it didn't use star grounding, relied on a dog slow LM324, had a lot of unnecessary parts for what seemed to be lowpass filtering. It relied on extreme capacitance to work around the grounding. It was the product of many experiments without an oscilloscope.
The 1st attempt used a MOSFET with full belt & braces snubber diodes. It quickly overheated & destroyed itself. It went back to a tried & true BJT with no snubber diodes.
...Continue Reading
It was finally time for a 3rd stab at a contact lens agitator. After years of levitation & home made linear motors, this one would be a tried & true laboratory shaker, using a stepper motor. The linear motor couldn't make enough thrust, was too noisy, & shed metal filings. The levitator had proven completely ineffective but looked neat.
There was hope a computer fan could do the job. Those turned out to use a dead simple half bridge. 1 pin is always 12V. The other 2 pins alternate going to ground. They spin in only 1 direction, no matter the polarity.
The next step was a traditional brushless gimbal motor. A 3 phase motor controller would have been ideal, but completely unaffordable. A pair of BJT's from a burned out lightbulb would do the job. They didn't need spudger diodes like MOSFETs. The same half bridge arrangement of a computer fan actually provided enough of a shaking motion when applied to a brushless gimbal motor.
After much effort, a C program for driving it with PWM wouldn't compile properly. The compiler choked on a counter equality comparison. After redoing it in assembly, PWM was once again a noisy failure. Even at 22khz, it was too noisy because the PIC at 8Mhz couldn't get the timing close enough. A linear regulator would lower the 20V input to control speed, the heat from which would heat the payload.
How to mount a regulator on a CPU heatsink to heat the payload....Continue Reading
That was disappointing. They lost 3 in 2007, when an oxidizer tank exploded. Like last time, they'll never release the cause of the accident. This was probably another oxidizer tank failure. The pilots would have been ejected by the blast. The guy in the left seat would have been the unlucky one, knocked by just the right piece of carbon fiber to knock him out.
There comes a point in a space program when enough people have been lost by the same cause that there is a definite safety issue in the management or the system. Hybrid rocket engines just may not be safe enough because they require too much gas under too much pressure for current materials. People have struggled with carbon fiber tanks for decades. They haven't been consistently able to contain a rated pressure.
It's hard to believe they'll be able to make another vehicle without any money coming in from customers. The plan was always to mass produce them, but only after the money was coming in from the 1st one. Dick Branson had slowed funding to a crawl. It's hard to slow it any further without stopping it.
It's yet another story of another guy giving his life in the quest to reach space. As long as space is just 62 miles away, they'll keep reaching for it & some won't come back. Maybe we'll lose 1 per decade. No-one died in the 1990's, when the number of people going up was at its peak. There hasn't been enough money since then. The 2010's are still benign compared to the 2000's.
Virgin Galactic/Scaled was the last to continue the legend of people coming to the high desert of Calif* to ride a vehicle into space, test pilots whose names no-one knew, who rode horses & drank at a run down bar. The legend is really over. Kazakstan ended up being the place for going into space. The new space cowboys drink Vodka & drive trucks with dashcams on the wrong side of the road.
