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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Backlash
From: Bruce Stark
Date: 2005 Nov 20, 14:52 EST
From: Bruce Stark
Date: 2005 Nov 20, 14:52 EST
Alex,
I may not be able to join in on your backlash experiment (Nov. 11 posting). For one thing, it'll be mostly rain, overcast, or fog around here for the next five or six months. But I'm interested, and hope others will take part. I've always felt that making contact by always turning the adjusting knob the same way was a waste of effort. Except perhaps for instruments with stiff pivots and index arms that might flex.
Friction in the pivots of my two sextants is so slight the index could be moved with a feather, and the index arms are quite stiff. A powerful spring forces the gear teeth together, and the design of the sharp teeth would seem to prevent any backlash there.
But some time ago I did my own experiment by measuring the sun's diameter, making an equal number of contacts turning the knob to the right and to the left while on the arc. Then the same off the arc. Sorting these out so as to isolate the effect of backlash from personal error (the way I see a contact when closing a gap, as opposed to the way I see it when pulling one image off of the other) there was no backlash effect whatever. The sun's diameter was measured accurately either way.
What surprised me was that there was only a slight effect from personal error.
But that was just one experiment with one sextant (a Tamaya).
Bruce
I may not be able to join in on your backlash experiment (Nov. 11 posting). For one thing, it'll be mostly rain, overcast, or fog around here for the next five or six months. But I'm interested, and hope others will take part. I've always felt that making contact by always turning the adjusting knob the same way was a waste of effort. Except perhaps for instruments with stiff pivots and index arms that might flex.
Friction in the pivots of my two sextants is so slight the index could be moved with a feather, and the index arms are quite stiff. A powerful spring forces the gear teeth together, and the design of the sharp teeth would seem to prevent any backlash there.
But some time ago I did my own experiment by measuring the sun's diameter, making an equal number of contacts turning the knob to the right and to the left while on the arc. Then the same off the arc. Sorting these out so as to isolate the effect of backlash from personal error (the way I see a contact when closing a gap, as opposed to the way I see it when pulling one image off of the other) there was no backlash effect whatever. The sun's diameter was measured accurately either way.
What surprised me was that there was only a slight effect from personal error.
But that was just one experiment with one sextant (a Tamaya).
Bruce
