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Denny Hair at General George S. Patton

Denny Hair at General George S. Patton

   Steve and I went to visit Midway Village for the annual World War II Days reenactment.  A couple weeks ago I finished a very detailed book on the Nuremberg Trials.  One of the speakers at the reenactment is Denny Hair who portrays General George S. Patton.  He is an avid Patton historian and likes to take questions in character from audience members acting as press core.  A couple years ago I asked the general what he "thought of our Russian allies" and the face he made got the entire audience to roar with laughter.  After reading my book on Nuremberg I wondered how the general felt about the idea of war crime trials.  There were two schools of though: one was to bring those who were responsible for starting the war and carrying out atrocities to trial.  The other was simply to shoot them all. 
   After talking with the general, Steve and I went in search of some of the lesser known groups in the war.  The Ukrainians were already gone, but we did spend some time talking to the Polish army and some Russian sailors.
   It is now officially fall.
   I meant to take an after picture, but forgot.  This is the before.  Over the summer months I do not run the oven on clean cycle.  Now that the weather has cooled off it was time for a good clean.  While the oven clean cycle is for the oven itself, the heat produced makes the top of the range hot.  This helps the oven cleaning chemical work.  I generally work to keep the oven fairly clean but it gradually builds up over the summer months and looks like this by fall.  After heating for about 2 hours I used some oven cleaner and without too much effort turn that entire surface white again.  The secret is having a hot surface.  Once it is hot, very little effort is needed to scrap off even months worth of baked on grim.
   One of many docks mostly underwater along Monona Bay.  The weather had cooled off but then warmed back up.  My ride to breakfast was around 64°F/18°C and very humid.  It is now completely dark at 5:30 am and still dark when I arrive to breakfast at 6:00 am.  This morning I was about 7 minutes early as there was a strong tailwind from the west.  The morning temperatures would fall all day.  By the time I left work the temperatures were barely 60°F/16°C and falling.  The humidity also dropped dramatically to around 60%.  With the strong headwind, cooler temperatures and low humidity I am glad I used a long sleeve shirt and leggings for the ride home.  After two weeks for riding each work day I was already tired, and with the strong wind I didn't feel like pushing hard.  So I had a slow but very pleasant ride home with a lot of stopping for photographs.  The clouds have been interesting the last couple of days, the trees are just starting to turn, and the feeling of fall is in the air.
   Did some experiments today with some stepper motors.  The only library I found that can control them was designed for use with a CNC machine.  It takes G-code.  That is more complected than I had hoped but I have worked with G-code before—when I made a giant fricking robot with vision and lasers for work.  I was able to do some basic control but never got the speed control as turned as I would have liked.  The stepper motors, for my first project, are just going to move a laser mirror around.  So I think I will look for a more basic control library.  Otherwise, I'm just going to have to strip this one down.

Last week I wrote about an experiment I did using a 100 watt white LED COB for a strobe light. This weekend my 100 watt blue LED COB arrived and I was eager to see if it improved the freeze effect of my strobe experiment. The short answer: no.

I started to have my doubts about the strobe duration I read about. 1/1000th of a second, or 1 ms, was what I was using. While I don’t remember exactly where I saw the number I had been searching for number used for photograph strobe lighting. So I went in search of other numbers. One product I saw was an LED strobe used for high speed photography. They listed light pulse duration between 20-1000 µs. My setup can do timings this fast so I decided to give it a try. The results: 100 µs light pulses stop a spinning fan blade.

The problem is, even with a 100 watts of LED light, a 100 µs light pulses isn’t much overall light. The product I was reading about uses 2,000 watts of LED light—20 times the light output I have available.

Time for a little math. I was using 1 ms light pulses at 100 watts which is 0.1 joules for energy. By switching to 100 µs pulses, I have 0.01 joules. I would need to dump in 10 times the power—1000 watts—to get the same amount of light energy. I could do a bank of 10x100 watt LED COBs, but there is one other thing to consider.

LEDs output is limited by their temperature. The temperature increases because there is a voltage drop across the diode in where the energy is turned into heat. Thus the current that goes through an LED must be low enough to allow the heat to escape. A 100 watt LED with the correct heat sink is rated for continuous usage. We are only pulsing the device for a 100 µs at a time, and at most once every 100 ms. This gives a duty cycle of 0.1%. I’ve read “Most high-brightness LEDs have an effective upper limit of 6X to 8X over current capabilities, based on a typical 150 microsecond (µs) pulse width and 0.15% duty cycle.” That means my single 100 watt LED should be able to handle between 600 and 800 watts for 100 µs. I would only need 2x100 watt LED COBs in order to produce 0.1 J light pulses.

1 comment has been made.

From Noah

September 19, 2018 at 8:14 PM

It's very interesting that there is only a certain limit to the tradeoff of duty cycle % to driving current. I'll bet that there are some wickedly complicated heat-transfer equations out there somewhere!