You'll find in the first post I mentioned a "removable secondary mirror with an integrated dew heating system". For the primary mirror there is the typical heated strap option that is readily available from numerous suppliers, and I am working on another system too! See, full of surprises.
For the primary mirror there is the typical heated strap option that is readily available from numerous suppliers, and I am working on another system too! See, full of surprises.
Alex - you would never put active heat directly into a primary mirror via a heat strap to stop it from dewing up , it would ruin the optical figure . Refractors are more forgiving as they tend to be wrapped around the dew cap and lenses have 4 times the surface tolerance anyway .
Typical truss dobs even without shrouds tend to be a little warmer in the mirror box which helps with preventing dewing - a scope with a completely exposed mirror is always going to be tricky.
question, are the carbon fibre rods pultruded or woven?
reason I ask is the first pic shows a number of them bowing. if pultruded, these tubes are designed for axial loads, that is compression and have low strength against radial forces, but then in a truss design, all members are either under tension or compression unless they cross a certain length.
the woven ones have fibres in different directions and resist deflection better, but are more expensive.
I presume you've done a lot of tests, but with a laser collimator in, does the laser move out of the primary when going from vertical to horizontal?
I'd suggest slightly thicker tubes or even square tubes. square tubes have lower deflection than round.
apologies if you've already considered all of this.
where does the Upper assembly sit in the box?
is the wood all cut by hand?
Yes, all you mentioned has been taken into consideration. The poles are pultruded ones. The bow that's induced into the poles was a deliberate design factor. As you noticed, the poles end up working against each other but working together. I have to leave the 3K woven poles as an individual custom choice as they are so much more expensive, and there is no mechanical advantage over pultruded poles for this application.
Yes, the secondary cage sits inside the mount-box when stowed.
No, the components are not cut by hand - hand cutting cannot produce repeatable accurate cuts.
Thank you Mike for the opportunity to launch my new baby at IISAC '14. It was a very daunting exercise, and my nervousness was very much on display.
Thank you to everyone who came along to my presentation too. I felt that the IISAC would be a great launch platform as there would be so many people who I am familiar with from here in IIS. That helped me a lot as it felt I was amongst family. The only shame was that Saturday night was overcast and I couldn't show of Marana's true skills under starry skies.
Thank you for all your questions, ideas and thoughts. Things were very positive about my venture. My next mission is to attend many of the other club based star parties. I'm hoping to have as good a reception at these as I did at IISAC '14.
Any other questions, you are most welcome to ask me in this thread or PM me.
I'm happy to say that the committee of ASNSW has approved me to promote Gondwana Telescopes at their South Pacific Star Party,
I will be at the Astronomy Bazaar with my telescopes, and if you would like to speak to me afterwards, you will be able to find me by looking for the "Gondwana Telescopes" flag banner:
To show my appreciation, I'm looking to hook up with the good folks from 3RF to share my 17.5" dob for some Sky Tour time with fellow SPSP attendees.
I've offered to do a sketching workshop, but with the schedule being quite full, my workshop will be on if there is inclement weather. However, if the weather is fine, but you would still like to have some instruction on astro sketching, you are most welcome to ask me for some time,
My sketches will also be available for purchase.
The Gondwana Telescopes website is only a couple of days away from publication. I will make an announcement when it is finally up and running.
Queensland Astrofest this July
I am also looking to attend the Qld Astrofest this July. I been given the greenlight to promote Gondwana Telescopes up at Duckadang. I am very much looking forward to Astrofest as I've been asked many times if and when I'd be attending,
Introducing Karee - our new strut ultralight telescope.
An Australian Aboriginal word for 'Sun', Karee is the latest addition to the Gondwana Telescopes stable of ultralight dobsonians.
Based around the design of my own 17.5" strut ultralight, it has proven itself over the last four years to be rigid, reliable, versatile, and capable of dealing with the rigors of long distance travel.
Karee is offered for apertures over 16" and up to 20". It's parallel strut design allows for multiple finder scopes to be placed on the secondary cage and coupled to the rear strut, or even for a smart phone, tablet or other wifi system to be mounted onto the strut. This not only eliminates the need for a stand alone stalk, but with the finder set on the secondary cage makes for a built in counterweight solution. When an eyepiece of excessive weight is used, the finderscope on the sec. cage is removed, there by re-establishing balance of the instrument, but the aiming of the instrument is still possible due to the second lot of finderscopes or the wifi system mounted onto the strut.
Karee is capable of incorporating servo motors to create a complete go-to solution. As with its little brother, Marana, encoder couplings come standard to provide as easy a transition to plug'n'play with a system such as Argo Navis.
Its highly collapsible design makes for a very compact stowed configuration, and a configuration that allows for the telescope to be fit into a car in its various smaller components, not as large units. The stowed telescope comfortably fits into the rear compartment of most SVU's, and still allows for ample gear to be packed around it. While we all look after our precious equipment, having a telescope that can deal with the rigours of long distance car travel removes much of the worry of an instrument that is overly fragile.
Karee's secondary cage can be made in one of two configurations: 1, as a single sheet of plywood as seen in the photos, or 2, as a more orthodox enclosed secondary cage. All to give the customer the most flexibility in their personal requirements.
Both Karee and Marana will be on show at the Queensland Astrofest this coming July. Here in NSW, both Karee and Marana feature regularly at the gatherings at Katoomba Airfield.
There are currently two Karee's in production for two customers - one 16" and a 20". Pictures of these two projects will be posted on the Gondwana Telescopes website and here as they develop.
Gondwana Telescopes - a new choice in dobsonian telescopes.
Gorgeous scopes, and nice to see an Aussie built, bigger apature dob that looks like it has been given the attention it deserves.
I'll certainly be pestering my family for one of these - tho' I fear it will have to wait some years
Just a quick quiz on the 'Karee'. Why did you go with a 4 vane spider instead of three vanes mounted 'with' each truss pole? I would have thought this would provide 'better' stability with one less obstruction.
Good point about the vanes. When I built the original Karee scope, I used the original spider that came with the scope I removed the optics from. The secondary cage is much more rigid than the force exerted by the vanes would begin to compromise the stability. The Al brackets flex before the cage is compromised.
I've never had a problem with this as the ply is very stiff. If the spider's vanes are in the same plane as the ply, the only significant advantage would be to save space by reducing the height of the cage. The new Karee scopes will have the vanes in the same plane as the ply.
Now, if a customer has an existing scope that they would like to reuse components from, I have all confidence in the stability of the secondary cage to place the spider in the same fashion as the original scope. The amount of force that the spider exerts on the ply is very small, and the Al brackets flex way before the sec. cage would begin to buckle.
Alex.
Last edited by mental4astro; 27-06-2014 at 11:38 AM.
Gondwana Telescopes will be at SPSP this May
