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Chriske
Kijkerbouw Urania
Reged: 08/15/04
Posts: 1937
Loc: Boechout, Belgium
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This Equatorial platform is not so difficult to build.
Basically it's nothing more than a few wooden planks, a polar axis and a wooden arc of a circle matching your latitude.
Usage :
1- Small to very large telescopes.
2- Reflector (mostly Newtontelescopes).
3- Transportable.
for clearness' sake only the mount is shown here.
Large image
Large image
Large image
Large image
Large image
Large image
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Chris
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Chriske
Kijkerbouw Urania
Reged: 08/15/04
Posts: 1937
Loc: Boechout, Belgium
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This is the one I'm refering to.. 
A very nice mount made by Ed Jones.
The mount in the drawings above is modified to match my latitude (51°N). Although it was rather difficult I managed to make the mount only 8" high.
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Chris
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Ed Jones
Pooh-Bah
Reged: 04/06/04
Posts: 1081
Loc: Sin-sin-atti
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Chriske,
Yes I think this is about as simple a platform as there is. How big a platform did you draw? Mine is only 3 inches high. I don't see your rocker box pivot. I ended up putting 2 drive motors on it and it tracks great. Everyone Dob should have one!
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Ed Jones
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Chriske
Kijkerbouw Urania
Reged: 08/15/04
Posts: 1937
Loc: Boechout, Belgium
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Ed,
I must admit, made this one a bit larger compared to the other mounts I drew for the 'DIY mounts thread'. I will use these dimensions for my owne large scope. This one is made for latitude 51°. The combination of these two factors made the mount a bit higher than yours. I'll draw a smaller later on.
And I'll forgot the Teflon pads indeed, I'll correct that.
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Chris
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Chriske
Kijkerbouw Urania
Reged: 08/15/04
Posts: 1937
Loc: Boechout, Belgium
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As promised the smaller one to fit the other scopes in the DIY Mounts thread.
It took me a few attempts to make this one as small as possible and at the same time not to high. I ended with a 'Ed' only 102 mm high. So not to bad for a mount at 51°N. Remember at higher altitude it is very difficult to keep this mount low. So I had to make some compromises.
Still very easy to build.
Large image Looking South.
Large image Looking west.
Large image looking north
Large image At the start of its tracking.
Large image Knurled tracking axis, like Ed's.
Large image At the end of it's tracking.
Large image Telescope lifted a few inches to have a better view at the mount itself.
Large image Very narrow spacing between the north bearing and the base of the mount.
Large image 8" Dob sitting on it's platform.
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Chris
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LateViewer
professor emeritus
Reged: 11/17/05
Posts: 606
Loc: Westchester NY
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Great. And a great link to the Ed Jones thread as well.
I will bookmark this thread for another day.
Al
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12.5" Discovery String Truss Dob
DSV-1 Alt-Az Mount
WO 66mm Petzval
Orion 127mm Mak with WO 2" Dielectric Diagonal
Celestron CG-5 GoTo
8.8, 14, 18, and 24mm Meade UWA Series 5000 EP
32, 40mm Orion Optiluxe EP
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Steven Aggas
sage
Reged: 04/15/08
Posts: 287
Loc: Arizona
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I agree the drawings look great, but the polar axis does not even come close the the center of gravity of the combined mass of the ota, rocker, ground board, and platform top, and would fall over faster than you can say "Look Ma, no hands!"....
The teflon pieces should be directly above the three bearings for a straight-through transfer of stress, thereby avoiding a cantelever situation and flexure/bouncing. This could easily turn a one second vibrate-after-a-thump scope into a 5 second vibrate-after-a-thump tracking scope easily....
The serrated drive roller may work but could be problematic if a scope has a high value of moment arm, whether by having a preferred stiffer alt-az motion of longer FL, especially when the acope is pointed east or west and moved in altitude where the result could be uncontrolled skipping across that roller. A drive that is engaged or disengaged to a sector might be preferred and give peace of mind.
I do like the representations of the pieces though.... Very cool.
Steven
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Mr. Wizard
Elements in Harmony I, an 8"f6 German Equatorial - Stellafane Winner,
II a 20"f4.2 Newt-Dob - Astrofest Winner,
III a 6"f3.5 Finder/Newt-Dob, and
IV a 36"f4.5 Newt-Dob - "If it's up there, it's in here."
www.DarkSkyObserving.com
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jdownie
professor emeritus
Reged: 02/24/06
Posts: 721
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Quote:
I agree the drawings look great, but the polar axis does not even come close the the center of gravity of the combined mass of the ota, rocker, ground board, and platform top, and would fall over faster than you can say "Look Ma, no hands!".... I do like the representations of the pieces though.... Very cool.
Steven
Seems a rather harsh judgement, given that these are illustrative renderings and Ed's design is proven, in real execution, don't you think?
John
John
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ATM project - a terrible waste of good Pyrex.
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Chriske
Kijkerbouw Urania
Reged: 08/15/04
Posts: 1937
Loc: Boechout, Belgium
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Quote:
Quote:
I agree the drawings look great, but the polar axis does not even come close the the center of gravity of the combined mass of the ota, rocker, ground board, and platform top, and would fall over faster than you can say "Look Ma, no hands!".... I do like the representations of the pieces though.... Very cool.
Steven
Seems a rather harsh judgement, given that these are illustrative renderings and Ed's design is proven, in real execution, don't you think?
John
John
Wait John,
Steven has someting to say that could be important here.
Most of you guys know by now I'm busy making a list of drawings to be used as quick overview by novice amateurs.
That does not mean I build them all myself. All mounts in this 'DIY mounts' thread are all built by someone.
Except three (I think) I've build all these mounts in that list. That includes platforms. My personal platform is the Boxmount A long time ago I also build a Poncet. But I did not build A 'Ed' mount - yet -
I think it's normal that someone who actually build this type of mount should warn me about flaws in my drawings.
In fact I'm a bit ashamed I did not inform myself about a mount I did not build myself before I started drawing it... 
Give me some clues here Steven, Ed, ....
I'll correct it.
Thanks..
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Chris
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jdownie
professor emeritus
Reged: 02/24/06
Posts: 721
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Fair enough, Chris, but I was referring to tone, 'and would fall over faster than you can say "Look Ma, no hands!"....', more than content.
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ATM project - a terrible waste of good Pyrex.
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Ed Jones
Pooh-Bah
Reged: 04/06/04
Posts: 1081
Loc: Sin-sin-atti
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John,
You have to go through the math to be sure COG is close. But if you use two drive motors as I did it will not slip even if the COG is a ways off. I knurled the shafts on this one but not on the last one proving to myself that knurling is unnecessary.
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Ed Jones
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Steven Aggas
sage
Reged: 04/15/08
Posts: 287
Loc: Arizona
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Thanks Chris.
Typically one can't use just a pin or roller bearing in the plane of the platform top piece as the CG is way too low and therfore with a scope on it be way too top heavy and tippy at any part of the rotation besides when the top plate is horizontal. Instead, a larger diameter sector is used to provide a 'virtual' polar axis, or if a roller bearing is used its on a pedestal to raise its center to pass through the CG. Here you can see the larger diameter sector, while here you can see one using the pedestal to accomplish the same thing, to raise the polar axis to pass through the calculated CG of the ota, rocker, ground board, and platform top piece. All of that must swing freely about the pole for the amount of travel available on the sectors.
The first link, but not the second, is a good example of teflon placement. All teflon pieces are directly above the center of each of their sectors. Additionally, metal sectors help reduce flexure when the teflon can't be directly above the secot as is found when the platfor is at the beginning or end of travel.
I've built both drive mechanisms for my platform, a D'Autumn style with a 125 pound 20"f4,2 on it, and the engaged drive sector is by far the best in terms of using it to do ccd imaging when it's not quite balanced in 3D. The amount of offset, which wasn't much, a few pounds force, is no problem for the one but was enough to skip on the serrated roller.
Steven
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Mr. Wizard
Elements in Harmony I, an 8"f6 German Equatorial - Stellafane Winner,
II a 20"f4.2 Newt-Dob - Astrofest Winner,
III a 6"f3.5 Finder/Newt-Dob, and
IV a 36"f4.5 Newt-Dob - "If it's up there, it's in here."
www.DarkSkyObserving.com
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jg3
sage
Reged: 05/27/07
Posts: 207
Loc: near Auburn, CA
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Quote:
I agree the drawings look great, but the polar axis does not even come close the the center of gravity of the combined mass of the ota, rocker, ground board, and platform top
Chriske's design is for 51 degrees latitude, and shows a low-CG scope upon it. That design runs into limitations at much lower latitudes, such as Arizona (33 +/- degrees, where Mr. Aggas hails), and also for tall scopes. That's where the CG would be difficult or impossible to place along the rotation axis, resulting in torque to the motor, draining the battery and/or upsetting its speed. There is also a little extra tipping risk early and late in the run cycle because the CG shifts. Allow for that by just making the platform bigger.
For a given tolerable tip angle, higher latitudes get some more time per run than lower latitudes. Figure that as part of the design. Also, the arc might need to be cut straight in the center for ground clearance, at lower latitudes. Again, just part of the design.
Those of us at lower latitudes and/or taller scopes usually solve the CG height problem with either a pedestal for the south pivot, or another arc instead of a pivot. (I'm designing mine with two arcs for a tall scope at 39 degrees latitude.) Maybe if we are nice to Chris, we will get to see some cool illustrations of such a design.
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Steven Aggas
sage
Reged: 04/15/08
Posts: 287
Loc: Arizona
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Quote:
Maybe if we are nice to Chris, we will get to see some cool illustrations of such a design.
I'd be interested in seeing illustrations of such a double arc design....
I built my platform for N43 and then five years later moved to Arizona at N33. Since the south pivot point uses three roller bearings to capture the edge and face, while the other two sectors ride directly on top of rollers, that tip required a heavy duty spring to pull the platform top back in contact with that sector-face touching bearing fortunately before an accident occurred with the scope and platform top sliding off to the north (platforms with bearings to hold all three sectors captive may have an advantage...). There was still a problem with the alt bearings compensating for the additional 10 degree tip of the rocker and that this tip shifted the CG relative to the three teflon pads with more weight on two at any one time. I built a wedge to make the scope level again but at the expense of the system CG being higher than the rotational axis. A steel plate placed on top of the platform top piece brought the CG back in line.
Lattitude changes are a big deal....
Steven
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Mr. Wizard
Elements in Harmony I, an 8"f6 German Equatorial - Stellafane Winner,
II a 20"f4.2 Newt-Dob - Astrofest Winner,
III a 6"f3.5 Finder/Newt-Dob, and
IV a 36"f4.5 Newt-Dob - "If it's up there, it's in here."
www.DarkSkyObserving.com
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Ed Jones
Pooh-Bah
Reged: 04/06/04
Posts: 1081
Loc: Sin-sin-atti
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My second platform has 2 sectors. One of the cool features is that it can be pushed back to start in 2 seconds since the Newport posts that drive it aren't knurled. I doubt if any other platforms can be reset so fast.
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Ed Jones
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Steven Aggas
sage
Reged: 04/15/08
Posts: 287
Loc: Arizona
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My reset time is close to that. The worm is released and re-engaged quite fast but the extra time comes in how fast I want to move a 150 pound structure that's not compact.... About 7 seconds is as fast as I've ever felt comfortable. The worm is spring-loaded to quickly disengage when released to save any teeth and the platform top has my hand on it at all times and moved to the beginning and worm reengaged.
I'm probably 70% of the way done with the design for the 36" which weighs in at 1400 pounds, plus the platform top expected to be 200 pounds. I'll still use the sping-loaded worm but have a mechanical advantage built in to rewind the massive top assembly back to its beginning.
Things left to do are the worm sector/gearbox selection using a 2" threaded rod at 4.5 thread per inch, servo v. stepper motor, and an azimuth adjust system to assist in polar alignment. With the 20"/platform I've used a crowbar to scoot the platform CW or CCW horizontally, but with the new scope and platform total system weight approaching 1800 pounds I'll need something else (besides a bigger crowbar).
Steven
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Mr. Wizard
Elements in Harmony I, an 8"f6 German Equatorial - Stellafane Winner,
II a 20"f4.2 Newt-Dob - Astrofest Winner,
III a 6"f3.5 Finder/Newt-Dob, and
IV a 36"f4.5 Newt-Dob - "If it's up there, it's in here."
www.DarkSkyObserving.com
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