Truss project

I am working on a 16 inch truss project that was abandoned by someone else and am working through some problems. It is a pretty traditional truss setup big and bulky. The Mirror box and cell weigh 45 lbs, The secondary cage weighs 7 lbs and will weigh about 11 with the focuser, secondary mirror and eyepiece installed. My mirror is 88 inch focal length.

Two questions. First when figuring the balance point do you use the center of the alt bearings or the edge? Second the original designer was going to use a 6 pole truss setup but when he designed the clamping mechanisms he blundered. The secondary cage has the clamps properly spaced at 120 degree intervals around the secondary cage ring. The mirror box however is square and the clamps have been mounted with a 90 degree angle and two 135 degree angles. If I do the trig and work out the poll lengths and mark them will this system work?

If not should I back up and use a 8 poll system at 90 degrees or change the secondary cage to reflect the 90/135/135 configuration?


Thanks
Dave

David,

Center of the bearings (point you rotate around).

I would go with the 8 poles. Uniform is simple. Simple is great.

Ed

Two questions. First when figuring the balance point do you use the center of the alt bearings or the edge? Second the original designer was going to use a 6 pole truss setup but when he designed the clamping mechanisms he blundered. The secondary cage has the clamps properly spaced at 120 degree intervals around the secondary cage ring. The mirror box however is square and the clamps have been mounted with a 90 degree angle and two 135 degree angles. If I do the trig and work out the poll lengths and mark them will this system work?

1. Use the center of the alt bearings. That is the axis of rotation.

2. You can make it work with what you have, but it is more difficult. I finished a similar project last summer, a 16" with 6 poles. The pole attachments are spaced 120 degrees apart on the secondary cage with an odd spacing on the mirror box. You can make it work, but there are a lot more details to work out, especially the pole connections. I used the Moonlight ball and socket connector to simplify this, but I still had to make some modifications. I did the trig to get an approximation for the pole lengths (3 different lengths), but reached the final length by trial and error and shortening the poles a little at a time.

Hope this helps,
Kevin

P.S. here's a picture of the unfinished scope.

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