I'm still not convinced, but I am willing to be convinced.
Here is what I think about after I read that paragraph:
Push down here
|
V
==================================================== <--- Shaft
| ^
| |
| Push up here
V
Load hangs here
It sounds like you are saying that the farther apart the "Push up" and "Push down" points are, the greater the bending force on the shaft.
I don't think so, yet anyway.
If we keep the "Loan hangs here" and the "Push up here" points the same distance apart, the torque will remain the same right?
And then if we move the "Push up" and "Push down" points farther apart, the amount we need to push down to counteract the torque is lowered right?
So we are pushing down less, on a longer lever arm. Which causes more deflection? I don't know. I'll spend some time on it, and get back to you.
> Now look at mine. The short shaft transfers it's load to the top of the
> right bearing (and the c.w.'s load to the top of the left bearing) before
> it can bend. Yes, we've increased the SHEAR load on the shaft and the
> load on the bearings by a tad (the left bearing is still carrying most of
> the scope's load and the counterweight's is on the right bearing), but
> reduced the shaft's bending load (a function of the shaft's length, which
> we shortened).
Does this mean that if I put the bearings ten feet apart, that the shaft will snap in the center due to the bending load? I just doesn't seem right to me yet.
I tell you what I'll do: I'll simulate both systems, and then tell you how they came out.
I am also completely willing to be convinced that closer bearing spacing is better just by talk alone if I can really understand it.
>
> (Andy asked) "How do you intend to control the tension on the DEC shaft?"
> (I responded) "I don't know what this means."
>
> Well, right now that scope would go whirling around the dec axis at the
> slightest push. You need some way to loosen it so you can move the scope
> in declination and then tighten it back down so it doesn't move.
Oh, I plan on making a circular collar larger than the shaft, and lining it with friction material, and having a screw thread through the aluminum plate that pulls the collar down so that the inside of the collar pushes down onto the top of the shaft.