Re: Kilian's Mount: Design changes.

Bob Madden (madden@netcom.com)
Sat, 29 Apr 1995 21:26:57 -0700 (PDT)

Lets see, I hope I can remember my structures. If the telescope were considered a free body (no counter weights) The force and moment acting on it would be such that it would want to move in the direction if the sum of the weight. But lets only consider the telescope having weight, thus the force. now to keep this body from moving in the direction of the force _AND_ from rotating there must be counter acting force and moment. Hope you have the picture. now lets counter the force somewhere, say the main mount, polar or tripod. what is left is the moment caused by the weight being at a distance from the center of the bearings (or couple reaction points). Now the farther apart the bearings are the lower the resulting forces. Infact whrn one bearing is directly under the tube force there will be no moment or couple. There fore the second bearing isn't doing any thing. My conclusion would be the farther apart you would put them (with in reason) the better. Now weight and space are a consideration, but I just don't understand the knits over this problem. Heck, the size of the shaft and the 3/8 thick plate for the size of the OTA are probably ample.

Friendly Bob

):-{])) <---- madden@netcom.com madden@svpal.org Remember amateur astronomers: "keep looking for the next Universe"

On Sat, 29 Apr 1995, Andy Steere wrote:

> Bear with me... hold your long printout so the dec shaft is horizontal and
> the scope is on the left. Ignoring the counterweight for a moment... the
> scope will push down on the bottom-left surface of the left bearing, which
> will cause the right end of the shaft to want to come up. The top surface
> of the right bearing stops it from doing this. The longer the distance
> between the bearings, the more bending force is exerted on the center of
> the shaft between them. The counterweights add to this force from the
> opposite end, causing the center of the shaft to bend "up" even more.
>
> 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).
>
> Also, in your design, the load from the bearings was being transferred to
> the 3/8" aluminum plate supporting them. In my design the bearings are
> mounted much closer to the thicker main housing instead of hanging out in
> the breeze. All the weight is being transferred to the ground and your
> 1-5/8" shaft, oversized bearings, and the main mount housing can deal with
> the weight better than the long thin aluminum plate you had supporting the
> bearings.
>
> The only positive thing about a long shaft I can think of in this instance
> is to give the mount better leverage on the slop in the bearings. Maybe
> Opticraft's design lets them get by with cheaper bearings. ;-) Don't use
> sloppy bearings and you don't have to worry about it.
>

Lots a cut text --------------

>
> Andy Steere
> dmislas@clark.umsystem.edu
>
>