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Re: Sextant averager
From: Gary LaPook
Date: 2010 Oct 12, 13:03 -0700
From: Gary LaPook
Date: 2010 Oct 12, 13:03 -0700
It took me a while to figure out how this averager works. At first I thought it was as described at: http://fer3.com/arc/m2.aspx?i=018062&y=200410 that it was simply and integrator that multiplied the displacement from the starting altitude by the time. But when I took one apart I was surprised to find that the time element was supplied by the ball moving across the disk and not by the rotation of the disk which actually supplies the altitude component. I finally figured it out, it is all in the last movement, turning the altitude knob back after the shot. I reasoned it out this way which might help in your understanding of this device, refer to figure 20 in the patent document at: http://www.fer3.com/arc/imgx/MA-2-Manual.pdf These examples should help. Starting with the altitude set to 30 degrees you start the averager and then immediately change the altitude to 40 degrees where it stays until the end of the averaging period, two minutes. Since, at the beginning the ball is located in the center of the disk that rotates when you turn the altitude knob, changing the altitude transmits no motion to the drum so the drum index dial doesn’t move. So when it comes to the point to rotate the altitude knob to move the drum index dial back to zero, no change is required and you read out the average as the final altitude, 40 degrees which is obvious since it stayed at this value for the whole period. Second example. Starting again at 30 degrees you start the averager running. Just before the end of the averaging period you rotate the altitude knob to 40 degrees and then the averager stops. When the altitude knob was turned the ball had reached the edge of the disk so it moved the drum the maximum amount possible and the drum index dial moved the maximum amount also. Now, when you rotate the altitude knob to move the drum index dial back to zero, it will move exactly the same amount as it moved when the altitude was changed from 30 degrees to 40 degrees so the altitude readout will return to 30 degrees as the average which makes sense since it stayed at this value for the entire shooting period. Third example. Again starting at 30 degrees you start the averager running and at the one minute point you change the altitude to 40 degrees where it remains to the end of the shooting period. At the one minute point the ball had moved only half way to the edge of the disk so when the altitude was changed to 40 degrees the drum index dial only moves half as far as it did in the second example. After the shot, when the altitude knob is rotated to move the drum index dial back to zero, the ball has reached the edge of the disk so the drum moves twice as fast as it did when the knob was rotated to change the altitude from 30 to 40 degrees. So now rotating the knob back towards 30 degrees the drum index dial reaches the zero position when the altitude readout has only gone back as far as 35 degrees which is the average. In the more normal case when there are variations in the altitudes during the shooting period the operation of moving the drum index dial back to zero moves the altitude readout back to the average of all the positions taken by the altitude readout during the two minute period. gl On 10/10/2010 5:43 PM, Gary LaPook wrote: > Here is the patent on the Dreimel-Black averager used in the Kollsman > sextant. The patent used an A-10 sextant to illustrate the invention. > > Also see: > > http://www.fer3.com/arc/imgx/MA-2-Manual.pdf > > > The following post describes the operation of the averager but has it > wrong since the ball moves from the center to the edge of the rotating > disk at a constant rate driven by clockwork and the rotating disk is > turned by the altitude knob which is exactly the opposite of this > description. > > > http://fer3.com/arc/m2.aspx?i=018062&y=200410 > > > > gl