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Forum Index : Other Stuff : 8th April 2007, Easter weekend
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Well its good to get a few days off. I finally got around to making the foam ribs for Trev. These are to make the plug for a 2 meter blade, and use profle NACA2410. I entered the figures into the old faithfull Warlock blade calculator and used the results to draw up the rib sections in Autocad. The blade calculator gave tips of only 70mm chord length, so these were scaled up to 100mm, and the points near the hub were scalled down to 300mm, as these were almost 500mm. Once I had all the profiles scaled to size, I nested them together to fit a piece of 25mm PVC foam Trev gave me for the job. To save material and machine time, I used something we call bridge cut, where the parts are joined together with little bridges. This means the router can stay down for longer. The cad work took about 2 hours, and the routing on the machine took about 1 hour. 
Added some panel meters to my battery box. I bought a couple of those cheap LCD panel meters from Dick Smith. Now these need 9 volts to run, but this 9 volts must be isolated from the voltage you are measuring, ie, you can not measure the meters own power supply. Oatley Electronics sell a little isolated power supply board for just this reason, http://secure.oatleyelectronics.com/files/K212notes.pdf, and in last months Silicon Chip magazine there was a article about it. But I found a cheaper way. The old network cards, the ones with the BNC coax connector, have a 5 to 9 volt isolated inverter on the circuit board. If you have one of these old network cards in the junk box, have a look for the model number on the inverter and do a google search. 
I found the data sheet for this one.... 
As you can see, they are tough little buggers, built to last. So to use these inverters, all you need is a 5 volt regulator, like a 7805 for a couple of dollars from Dick Smith, a 10uF cap on the 7805 input, a 1uF cap on the 7805 output, and thats it. Bet you wish you never threw out those old network cards now dont ya 
I wanted my panel meters to read battery voltage and amps. Volts is easy, but for amps I needed a shunt. I ended up using a length of 1/4 inch threaded rod, about 170mm long. I found that 120mm was the magic length for the shunt measurement, 120mm gave 10mV per amp. So my amp meter reads +-199 amps,with a resolution of 0.1 amps. 
Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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