93 replies to this topic

[skaven]

It's hard to tell without fully assembling the scope and actually pointing at something, whether the new tubing is better or worse (or the same) as the existing tubing.  My hope is that the thicker sidewall results in a stiffer bearing surface that has less of a tendency to "stick" when the scope comes to rest.

 

If I don't notice any improvement, I will try the soap.

 

I was able to get the scope out for a full night last night with the new tubing installed.

 

I can say, without any hesitation, that both the friction and the stiction are GREATLY reduced with the thicker, opaque tubing.

 

However, it turns out this isn't necessarily a good thing.  The reduced stiction is great, because it makes pointing/tracking much easier.  However, the reduced friction is not so great -- the balance became so critical that simply removing the eyepiece from the focuser caused the scope to drift back up to vertical.  That was REALLY frustrating, because I'd find the object I was looking for in my 30mm eyepiece, then try to swap it out for a higher-power eyepiece, only to find when I came back to the scope, that it had slipped several degrees toward the zenith.

 

I ended up wrapping a bungee cord around the UTA and shimming some rocks from around the observing site under the elastic to improve the balance.  However, this was a game of cat-and-mouse: when the scope was aimed lower toward the horizon, I had to remove some counterweight from the UTA to keep it from slipping *down* when an eyepiece was installed.  And when observing closer to the zenith, I had to add more counterweight to keep it from slipping further up toward the zenith.

 

So it seems my current combination (2 well-polished coats of StarBrite marine polish + new base tubing) is ultimately a fail.  In the spirit of only changing one variable at a time, I'll try adding the soap treatment next.  If that doesn't work as planned, I'll swap the new base tubing for the old one, and if it's still no good, remove the soap (which would put me back to square one).

[areyoukiddingme]

Hmm, I noticed in your previous description that you'd like low stiction, and high friction.

 

My thinking is that you want 'highish' stiction, and low friction. 

 

When I use the term stiction, I'm referring to the static friction between the scope and the tripod ring. I want that to be moderately sticky, because I want to be able to switch eyepieces or just sit in one place without the scope drifting. Over time I notice that the stiction does increase, and can be returned to 'normal' with a new application of turtle wax. But that's almost purely aesthetic. I find the scope has performed pretty much flawlessly for at least a year in this state.

 

But once that static friction is overcome, it is pleasant to have a nice smooth, and relatively low friction because that makes it easy to move the scope and track objects. Smoothness is the key; if the surfaces have an uneven supply of grease, then it's likely to become a bit herky-jerky. That's definitely time for new wax.

 

I do not know how soap will perform in this scenario, but I have never heard of anyone else using a Portaball with this solution. That's not reason not to try it, but there do appear to be several people happy with the turtle wax solution. Given that this works for others, that suggests to me that there's either some substance on your sphere and/or contact surface that is interfering with that application.

[skaven]

My thinking is that you want 'highish' stiction, and low friction. 

 

When I use the term stiction, I'm referring to the static friction between the scope and the tripod ring. I want that to be moderately sticky, because I want to be able to switch eyepieces or just sit in one place without the scope drifting. Over time I notice that the stiction does increase, and can be returned to 'normal' with a new application of turtle wax. But that's almost purely aesthetic. I find the scope has performed pretty much flawlessly for at least a year in this state.

 

But once that static friction is overcome, it is pleasant to have a nice smooth, and relatively low friction because that makes it easy to move the scope and track objects. Smoothness is the key; if the surfaces have an uneven supply of grease, then it's likely to become a bit herky-jerky. That's definitely time for new wax.

 

We're definitely using the same definitions for stiction and friction in this case.  And your explanation does indeed make sense -- some degree of stiction is necessary to ensure that slight imbalances of the scope (e.g. due to eyepiece swaps) don't trigger movement.  The problem, in my case, is that the act of overcoming the stiction to get the scope moving, is itself a "herky-jerky" action.  Increasing pressure is applied in one direction, and then all of the sudden, *pop*, the stiction breaks free and is replaced by very low friction, and the result is a large, sudden movement, when only a small movement was desired.  Even if I keep the stiction relatively high, high friction is necessary to ensure that once the static friction is overcome, that the scope doesn't slip by a large amount, thus allowing finer control over pointing.

 

My experiments with different bearing and lubrication materials is ultimately an effort to find the best balance of stiction and friction -- one that ideally gets stiction at a level where the scope "sits still" when I change eyepieces, but that is still easy to make fine pointing adjustments with.

[Pierre Lemay]

However, the reduced friction is not so great -- the balance became so critical that simply removing the eyepiece from the focuser caused the scope to drift back up to vertical.  That was REALLY frustrating, because I'd find the object I was looking for in my 30mm eyepiece, then try to swap it out for a higher-power eyepiece, only to find when I came back to the scope, that it had slipped several degrees toward the zenith.

Now THAT I can relate to! On my 20 inch Ball scope, which uses a 30 inch diameter plastic hemisphere, I could never remove the 2.5 pound, 20mm ES100 eyepiece (except when viewing near zenith) without the scope trying to climb up. Removing a half-pound, 82 deg AFOV 1.25" eyepiece does not make the tube move. But removing a 2" 100 deg AFOV will.

 

I know a lot (but not all) dobs have similar problems. In a dob the problem can be considerably reduced through proper design in the azimuth bearing positions and trunion size. Plus, its easy to add breaks, clutches or springs. No easy solutions with a ball scope: balance must always be nearly perfect. 

 

That's why I designed this eyepiece turret. The 20mm eyepiece is always on the UTA. It's part of the counterweights used for telescope balance. When I need to find an object I rotate the 20mm eyepiece in the light path. For higher power views, I swing the 20mm eyepiece to its parking position and a 1.25" higher power eyepiece is now in the optical path. 

 

[skaven]

 

I know a lot (but not all) dobs have similar problems. In a dob the problem can be considerably reduced through proper design in the azimuth bearing positions and trunion size. Plus, its easy to add breaks, clutches or springs. No easy solutions with a ball scope: balance must always be nearly perfect. 

 

That's why I designed this eyepiece turret. The 20mm eyepiece is always on the UTA. It's part of the counterweights used for telescope balance. When I need to find an object I rotate the 20mm eyepiece in the light path. For higher power views, I swing the 20mm eyepiece to its parking position and a 1.25" higher power eyepiece is now in the optical path. 

 

Wow, that is quite an ingenious design!  How are you able to adjust focus?  I imagine you have both eyepieces set more-or-less at their focus point when rotated into the optical path, but how do you achieve fine focus?

[klim]

 

 

I know a lot (but not all) dobs have similar problems. In a dob the problem can be considerably reduced through proper design in the azimuth bearing positions and trunion size. Plus, its easy to add breaks, clutches or springs. No easy solutions with a ball scope: balance must always be nearly perfect. 

 

That's why I designed this eyepiece turret. The 20mm eyepiece is always on the UTA. It's part of the counterweights used for telescope balance. When I need to find an object I rotate the 20mm eyepiece in the light path. For higher power views, I swing the 20mm eyepiece to its parking position and a 1.25" higher power eyepiece is now in the optical path. 

 

Wow, that is quite an ingenious design!  How are you able to adjust focus?  I imagine you have both eyepieces set more-or-less at their focus point when rotated into the optical path, but how do you achieve fine focus?

 

It would appear that each eyepiece is situated in its own helical focuser.

[Pierre Lemay]

Klim is correct: each eyepiece on the turret has it's own focuser. In the interest of keeping the UTA lightweight, I made two helical crayford type focusers: a 2" one and a 1.25". The entire turret, with its double focuser and all hardware for mounting and turret rotation weighs just under 1.5 pounds. That's less than a single, dual-speed Feathertouch focuser.

Collimation is always done through the 1.25" focuser since it is in this one the shortest focal length eyepieces (highest power) will be used.

[Earthbound1]

Hey, has anyone tried graphite as a dry lubricant? Sorry it's gray and the portaball is white, but it might provide an answer... Worth trying in my opinion. Could be wiped off with viva paper towels and soap... Someone should try either powdered graphite or taking a number 2 pencil to it. Talc might be worth trying too, not as slick as graphite but better looking... Just my 2 cents.

[sedmondson]

Old thread but ...

 

I have a 12.5" portaball from about 1999 (?). Peter met me halfway from my house to deliver the scope. Zambuto mirror is awesome. Unfortunately, it doesn't get as much use these days as it should.

 

Periodically I have to clean the ball with denatured alcohol (methanol) and then apply a thin coat of marine polish (Starbrite?). Works well for me. You want enough stiction so that tube does not move during eyepiece changes, yet moves smoothly with small nudges while tracking at high powers (300x).

 

Also I have not had much problem with the electrical system, although I do sometimes blow a fuse. I have only had to replace the battery once in 20 years. Oh, and once for the electrical heater on the secondary mirror.

[Earthbound1]

I'm pretty sure I've conquered the stiction/balance issues with ball scopes. Ferric composite shell, magnetized base with PTFE over the magnets. I have to play with different strengths of the magnets to get it perfect, but I plan on doing that soon enough. Depending on the size ball and weight therein will probably determine how strong a magnet it needs. I hope to document all this in the next few months. Waiting on my next mirror and build materials, but early tests show no reason whatsoever why this is not the answer.

[ltha]

In the late 90s I read something about Portaball and asked for their brochure. At the time I was living in Long Beach, CA and for any chance at "dark skies" had to drive anywhere from two to four hours so the portability was a huge plus, as were the Zambuto optics. After a chat or two with Peter Smitka I ordered a 10" Portaball and then waited for it to be built. From the moment I unpacked the scope and set it up for the first time I knew I had made a great decision. What a marvelous scope! My best ever view of Mars was through the 10"PB easily beating the 6" refractor I had at the same time. I liked the scope so much I ordered a 12.5" PB with a Roundtable tracking platform. Selling the 10" was hard as it had been such a great scope, but the 12.5" gave a bit better performance especially on globulars and deep sky. I still have the 12.5" along with a Starmaster 18", 5" Takahashi FC-125, a unique Cave 12.75" with Quartz primary, and TEC200ED. The PB holds its own against everything and bests them in terms of portability. Many years ago I had friends over to look at Saturn. At the time I had the 12.5" PB, a Takahashi FS-152, a Cave 8" F/8 and a couple of smaller APOs. One of my friends asked "If you could only have one telescope what would it be?" Without a seconds hesitation I said, "The Portaball!" That is still true today. 

Edited by ltha, 02 March 2019 - 01:18 PM.

[ltha]

My 12.5” PB. A Smitka original. I did spend close to an hour with Peter on the phone searching for an electrical gremlin. That was years ago and so far so good!

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Edited by ltha, 02 March 2019 - 10:00 PM.

[SkyRanger]

 

 

 

Who needs a shroud in N AZ?

 

GG

Edited by SkyRanger, 03 March 2019 - 08:02 AM.

[peleuba]

My 12.5” PB. A Smitka original. I did spend close to an hour with Peter on the phone searching for an electrical gremlin. That was years ago and so far so good!

 

Larry -  in Peter's day, no two Portaballs were wired exactly the same.  

 

 

 

Who needs a shroud in N AZ?

 

 

 

Gordon - I've always been jealous of your clear, dry, high desert environment.

  

I have recently just performed some upgrades to my Portaball.  I have owned both a PB-12 and 4 iterations of the PB-8.  I still own a PB-8 purchased from Dave Jukem at Mag1 once he redesigned the new, thin, machined aluminum uppercage.      Its my favorite telescope; the one I'll never part with.  But that's not to say its perfect.  On the newer PB-8's Dave offered a boundary layer fan that was tiny.  Its basically a 1"x1" fan that did not move a lot of air and in my observing conditions worked marginally.  To this end, I reworked the boundary layer system and replaced the small fan with a larger more efficient model.

 

The battery powering the PB-8 is 12V but only rated at 1.2 amps.  It supplies the secondary dew heater, main rear cooling fan, boundary fan, Rigel Quickfinder and the dew heater built into the Quickfinder.  I replace the battery once a year or so and use a microprocessor-controlled modern de-sulphating trickle charger that's always connected when not in use.  And, in the past, on all-nighters, I have run out of juice (not me, the telescope).  To remedy this, I added a second identical battery wired in parallel - doubling the capacity (amp hours) while maintaining the existing voltage (12V).

 

I also encased each of the anodized truss poles in heat shrink tubing as well as updating the sphere truss connectors with the new clamping style that just became available from Mag1.  The combination of heat shrink tubing and new connectors slightly improved the vibration dampening time.

 

Pics below show the new truss connectors on the sphere, the tiny stock PB boundary layer fan, the new larger fan I installed and the addition of a second Mag1 battery tray for a total of two.

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Edited by peleuba, 04 March 2019 - 01:07 PM.

[Jeff Gardner]

I own 2 Pballs, A 12.5" bought in 1997 and an 8" F6 bought in 2000. Peter was an interesting guy and we enjoyed hanging out with him every summer at the Cherry Springs Star Party. The scopes were amazing, not so with the electronics. Anyone who looked through either scope were always blown away with the views. The user friendly design couldn't be beat for public outreach. A real crowd pleaser RIP Peter!

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[SkyRanger]

Larry -  in Peter's day, no two Portaballs were wired exactly the same.  

 

 

 

 

 

Gordon - I've always been jealous of your clear, dry, high desert environment.

 

  

 

Paul, 

Yes, Arizona is blessed with some great skies, but also with rapidly falling temps at night fall.  This winter has been unusually wet and snowy so my astro time has not been up to par.

 

My 12.5" went back to PB World Headquarters for refurb over a year ago. I now have the lightweight upper ring, upgraded electrical, and Moonlight connectors.  It also came with the small boundary layer fan which I should replace with something larger, encouraged by your example.  No one has ever accused me of being coordinated, and I found the small upper ring awkward, so when the 8" f6 went back, I kept the older connectors and traditional upper cage. The main improvements were improved electrical, some small changes to the cell (I think.) a FT focuser, and new CZ quartz mirror.

 

I do need to get some teflon tubing to replace all my bearings in the stands and the Round Table platform.

Gordon G

[peleuba]

My 12.5" went back to PB World Headquarters for refurb over a year ago. I now have the lightweight upper ring, upgraded electrical, and Moonlight connectors.  It also came with the small boundary layer fan which I should replace with something larger, encouraged by your example.

 

 

Gordon,

 

I am certain the new truss connectors are an original Dave Jukem/Mag1 design and not Moonlight.  The Moonlite connectors I have seen are not like the metal ones that Dave makes. 

 

Adding a larger boundary layer fan requires some thought in that an on/off switch is part of the circuit as well as the new fan being quite a bit larger then the existing fan.  You'll need to create a new fan mount out of sheet metal and then splice the new fan wires in down-current from the switch.   

[peleuba]

I own 2 Pballs, A 12.5" bought in 1997 and an 8" F6 bought in 2000. Peter was an interesting guy and we enjoyed hanging out with him every summer at the Cherry Springs Star Party. 

Yep - me too.  Cherry Springs is my dark sky sight of choice.  I try to get there 4 or 5 times a year for a week at a time.

[mic1970]

Great thread.

[areyoukiddingme]

So far as electrics go . . . 

 

I didn't have many issues with mine. I had a large lead acid battery in the cell, which ran the center/bottom mounted fan, the Rigel finder, and the secondary heater.

 

The only thing that would play up was the Rigel finder, and I never used the secondary heater as it's just not an issue in coastal CA.

 

So after some mulling, I decided to remove all of the electrics and replace the Rigel with a standard battery powered unit (and keep a couple of extra watch batteries in my case).

 

That has worked out well so far, with the exception that my battery install is actually fairly poor and has failed twice. I need to get the soldering right.

 

Oh, and I also experimented with adding a potentiometer to the fan, but wasn't happy with the results. I'll probably try installing a boundary layer fan at some point, but I'm skeptical it will work well in the mostly enclosed sphere.

 

Does anyone have tips on that? I assume that turbulent air will bounce off the walls of the sphere.

[GeneT]

In 1997, I made a mistake in purchasing a 20 inch Obsession classic--too much hassle in loading, setting up, and reloading in a vehicle. Peter Smitka's concept--the largest possible telescope that was easily portable intrigued me. I sold my Obsession, and purchased a 12.5 inch Portaball. I have enjoyed it for more than 20 years. You can't use DSC's and you can run into balance issues with heavier eyepieces. I bought a Tom O Platform, which was designed specifically for my telescope. It worked great, but now I rarely use the Platform. Just find, and nudge to keep the object in view. The Portaball is fun, and easy to use. You can easily spin the telescope to place the eyepiece exactly where you want it. It is very easy to load and set up. I put the telescope on my front seat, secured with a seat belt. The accessories are then placed in empty spaces in the vehicle. The optics are excellent, and the 12.5 inch Portaball performs outstandingly on all objects. Planetary detail is sharp and detailed. Deep sky objects show up very well at dark sky sites. I had purchased an 18 inch Ultra Compact. My Portaball gave better planetary views than the UC, however the UC had twice the light gathering capacity and sucked in the deep sky objects much better. I don't know of Mag 1 still exists and makes the excellent Portaball. If I were buying a new telescope, I don't know if I wouldn't buy a different model. However, I do not plan to buy a new telescope, and I believe my 12.5 inch, F5 Portaball is my last, and my 'forever' telescope.   

[sedmondson]

Jeff,

good to see a picture of Pete again.

 

I never met anyone who did not like the Portaball. The anit-dew (heated) QuickFinder was a great idea, and I don't know why it was never offered on the open market.

 

The only possible drawback to the Portaball, which is also one of its attractions, is the lack of DSCs; it is strictly a push-to, star-hopping scope. And this thread is making me want to break it out again. Lately I've been enjoying a 130GT and Mewlon 210 on a DM-6 mount with Nexus wifi to iPad running SkySafari, a completely different (but still push-to) experience.

 

And I've never felt a need to upgrade my Portaball. I guess at some point the mirror may need some attention.

[Jeff Gardner]

Thought everyone would enjoy this  picture. This image was from a jealous club member who wished he was a Pball owner! LOL

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Edited by Jeff Gardner, 06 March 2019 - 09:23 AM.

[peleuba]

 

 

Oh, and I also experimented with adding a potentiometer to the fan, but wasn't happy with the results. I'll probably try installing a boundary layer fan at some point, but I'm skeptical it will work well in the mostly enclosed sphere.

 

Does anyone have tips on that? I assume that turbulent air will bounce off the walls of the sphere.

 

 

Turbulent air is not the main issue - though it can cause problems.   The primary concern is the mirror is a heat sink and there is a temperature differential between the air that hangs very close to the surface of the mirror compared with the rest of the air in the sphere.  This temperature delta creates a boundary between the different air masses inside the sphere.  In the Portaball, the fan mixes the air up so that the starlight is traversing a homogeneous air mass.   IMO, the slight turbulence caused by the fan is less damaging to the image then having the light path traverse two distinct air masses, twice. 

Edited by peleuba, 06 March 2019 - 10:32 AM.

[peleuba]

I don't know of Mag 1 still exists and makes the excellent Portaball. If I were buying a new telescope, I don't know if I wouldn't buy a different model. However, I do not plan to buy a new telescope, and I believe my 12.5 inch, F5 Portaball is my last, and my 'forever' telescope.   

 

Gene - Mag1 is still around.  Its owned by the machinist who manufactured all of the parts for Peter.  See this post in the this thread:

 

https://www.cloudyni...ises/?p=7898733