Perseid's Truss Tube

Here is the place to talk about all those equipment(Telescope, Mounts, Eyepieces, etc...) you have. Not sure which scope/eyepiece is best for you? Trash it out here!
User avatar
ariefm71
Posts: 2304
Joined: Wed Jan 28, 2004 4:15 pm
Location: bedok

Post by ariefm71 »

the bible of truss dob making and a must have reference for all dob owners ...
http://www.globaldialog.com/~obsessiontscp/Book.html
User avatar
kayheem
Posts: 1039
Joined: Tue Sep 30, 2003 9:59 am
Location: Sennet Estate

Post by kayheem »

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
User avatar
Airconvent
Super Moderator
Posts: 5804
Joined: Tue Sep 30, 2003 11:49 pm
Location: United Federation of the Planets

Post by Airconvent »

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
The Boldly Go Where No Meade Has Gone Before
Captain, RSS Enterprise NCC1701R
United Federation of the Planets
User avatar
kayheem
Posts: 1039
Joined: Tue Sep 30, 2003 9:59 am
Location: Sennet Estate

Post by kayheem »

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
Posts: 255
Joined: Mon Oct 06, 2003 10:42 am

Post by elton »

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!
User avatar
ariefm71
Posts: 2304
Joined: Wed Jan 28, 2004 4:15 pm
Location: bedok

Post by ariefm71 »

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?
User avatar
VinSnr
Administrator
Posts: 2310
Joined: Sun Sep 28, 2003 7:01 pm
Location: Andromeda Galaxy

Post by VinSnr »

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
Posts: 255
Joined: Mon Oct 06, 2003 10:42 am

Post by elton »

I'm always open to a sale if there are sincere buyers. Aperture fever strikes from time to time and 14" beckons....
User avatar
Airconvent
Super Moderator
Posts: 5804
Joined: Tue Sep 30, 2003 11:49 pm
Location: United Federation of the Planets

Post by Airconvent »

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
The Boldly Go Where No Meade Has Gone Before
Captain, RSS Enterprise NCC1701R
United Federation of the Planets
User avatar
kayheem
Posts: 1039
Joined: Tue Sep 30, 2003 9:59 am
Location: Sennet Estate

Post by kayheem »

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
Post Reply