Perseid's Truss Tube

ariefm71 · Post by **ariefm71** » Fri Nov 19, 2004 12:31 am

the bible of truss dob making and a must have reference for all dob owners ...
http://www.globaldialog.com/~obsessiontscp/Book.html

kayheem · Post by **kayheem** » Fri Nov 19, 2004 8:14 am

ariefm71 wrote:kay heem, is this shift related to the use of four poles instead of eight? if this is the case, how bad was it when you're using the two poles last time for the 10" dob? i'll be using four 1" poles at the corners and tighten them using ball and socket clamps ordered from moonlite.
btw, my kriege&berry book just arrived, reading the first chapter now ...

Hi Arief,

It is not so much the number of poles, but the arrangement of the 8 truss tubes to form a solid structure that resists the shift. My old design was bad enough to feel it when pushing the upper cage to move it. I suppose if you use the much smoother bearing which I had installed (but not tested), it would be much better.

Kay Heem

Post by **Airconvent** » Fri Nov 19, 2004 2:24 pm

kayheem wrote: Hi Arief,
It is not so much the number of poles, but the arrangement of the 8 truss tubes to form a solid structure that resists the shift. My old design was bad enough to feel it when pushing the upper cage to move it. I suppose if you use the much smoother bearing which I had installed (but not tested), it would be much better.
Kay Heem

Hi Kay Heem
Would the problems you describe be so significant or it will only affect high magnification views like Planets? If its not too bad, it could be a good compromise for simplicity, weight and price...

rich

kayheem · Post by **kayheem** » Fri Nov 19, 2004 3:15 pm

Airconvent wrote: Hi Kay Heem
Would the problems you describe be so significant or it will only affect high magnification views like Planets? If its not too bad, it could be a good compromise for simplicity, weight and price...
rich

The shift will only occur on moving the scope. Once the force is released, it *should* spring back. Each person may have their own level of tolerance for such things, so better to try it out personally first.

Kay Heem

elton · Post by **elton** » Sat Nov 20, 2004 5:24 pm

kayheem wrote:
Hi Rich,

No, it is not 'parallelogram error' but 'parallelogram shift'. If you fix the mirror box and apply a lateral force to the upper cage, does the upper cage shift or move? If it does, there is parallelogram shift. If you can visualize it, the upper cage is displaced laterally over the mirror box and forms a paralleogram with the truss tubes instead of forming a rectangle.

That is why most truss dobs utilize the standard serrier truss configuration. I believe the teleport also suffers from a bit of this, but is not as bad, as the truss tubes extend further down the deep mirror box. Elton, please correct me if I am wrong.

Kay Heem

Kay Heem,
The teleports' truss tubes are secured at 2 points in the deep box, one at the bottom and one at the top of the box. This eliminates the problem of weakness at the joints. Any weakness in the setup comes from flexture of the bogen struts. The upper assembly is very light so unless you are binoviewing Pentax XLs, it should not be a problem. I'm sure there is some shift because the setup looks so flimsy, but this at the eyepiece collimation is maintained except when going down to close to 0 deg altitude. I guess if Tom Knowe was not satisfied with his design, he would not have use it on his 14" Teleports. I think Pereid is on the right path. Would like to get one for an Aussie trip next year!

ariefm71 · Post by **ariefm71** » Sat Nov 20, 2004 9:42 pm

I think Perseid is on the right path. Would like to get one for an Aussie trip next year!

hi elton, maybe you might consider selling your 10" teleport and get cc's portaball + perseid's 8" f/6 dob structure.
you can use the portaball in singapore or mersing, if you want to travel overseas, just put the 8" zambuto mirror into perseid's airline portable structure and carry on board. how's that?

Post by **VinSnr** » Sun Nov 21, 2004 12:02 am

ariefm71 wrote:
I think Perseid is on the right path. Would like to get one for an Aussie trip next year!
hi elton, maybe you might consider selling your 10" teleport and get cc's portaball + perseid's 8" f/6 dob structure.
you can use the portaball in singapore or mersing, if you want to travel overseas, just put the 8" zambuto mirror into perseid's airline portable structure and carry on board. how's that?

Dude, asking him to sell his teleport is like asking our goverment to remove all taxes and COE.

elton · Post by **elton** » Sun Nov 21, 2004 3:07 pm

I'm always open to a sale if there are sincere buyers. Aperture fever strikes from time to time and 14" beckons....

Post by **Airconvent** » Sun Nov 21, 2004 5:34 pm

elton wrote:I'm always open to a sale if there are sincere buyers. Aperture fever strikes from time to time and 14" beckons....

well Elton...you should get a car first...after that, all the big scopes seems so accessible, right?

rich

kayheem · Post by **kayheem** » Tue Nov 23, 2004 12:44 pm

OK, for all you guys looking for a portable truss dob, take a look at this:

http://lib1.store.vip.sc5.yahoo.com/lib ... eshow.html

Kay Heem