Re: Dec backlash adjustment
On 5/16/2025 12:32 AM, Oberon510 via groups.io wrote: Hi,
I have been getting some complaints from PHD2 that my Dec backlash is high and I used this video to adjust the spring loaded worm gear ".
It didn't make much difference and now I am about to clean and regrease the worm gear but hoping for some more advice/pointers on other things to look for or do as part of the process.
Any guidance appreciated.
Thanks,
Ken Hi Ken, In my experience with my GM811, I was never able to get my raw (uncompensated) DEC backlash below about 2000mS (two seconds) by merely adjusting / tweeking / re-greasing.? And that was after carefully doing the worm bearing squeeze and setting a value for TVC.? Sometimes it was better.... and sometimes it was much much worse.? Pointing location and balance had major impact on the amount of backlash. You can adjust the value of the TVC parameter in Gemini2, which will compensate for a fixed amount of backlash.? TVC is actually my preferred backlash compensation because it runs at about 10X the guide speed (unlike PHD2's compensation which runs in real time) so (for example) 2000mS of backlash compensation occurs in about 200mS using TVC.? But there's a BIG catch..... if your uncompensated backlash changes over time and ever drops below the amount of TVC compensation, the system will oscillate.? In my experience, the total system backlash was variable enough that even with a carefully chosen value for TVC, PHD2's backlash compensation (which was in the area of 2000mS give or take a lot) would occasionally fall to near zero and DEC would oscillate.? Reduce TVC and try again and you eventually end up with a very low value for TVC.... So in desperation I did a deep dive into the system and identified several suspect areas, most of which were inherent design choices or machining limitations. I made several mechanical changes to the DEC (and RA) drives (some simple and some not so simple), run my clutches very loose, and my backlash is now very consistent.? I also made and installed a 3rd axis counterweight to compensate for the fact that my filter wheel shifts the center of mass of the scope off the DEC axis slightly. After all this, and with a carefully chosen value for TVC, PHD2's backlash compensation CONSISTENTLY runs between about 200mS and 800mS.? If it ever rises above 800mS I know it is time to re-adjust the "spring loaded worm" pressure, which is typically required twice a year due to seasonal temperature changes. If there is any interest (and if it is allowed here) I can go into more detail.? All but one of my modifications are non-destructive, fully reversible and of varying difficulty.? But the bottom line is the combination of bearing choices and machining tolerances in the GM811 added up to quite a bit of backlash (and significant 74 second periodic error too).? After my modifications.... "it just works" and I get very good tracking and guiding.? A bad night for me is anything above 0.6" RMS.? On very stable nights (Detroit metro area) I have seen it in the high 0.3" RMS range.? My 240 second periodic error is almost un-measurable.? But more importantly, it does that night after night regardless of where I am pointed. Maybe a longer answer than you were looking for, but it is a complicated subject. Paul -- Paul Goelz Rochester Hills, MI USA pgoelz@... www.pgoelz.com
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Hi,
?
I have been getting some complaints from PHD2 that my Dec backlash is high and I used this video to adjust the spring loaded worm gear "https://www.youtube.com/watch?v=LGmj3bEDVNM".
?
It didn't make much difference and now I am about to clean and regrease the worm gear but hoping for some more advice/pointers on other things to look for or do as part of the process.
?
Any guidance appreciated.
?
Thanks,
Ken
?
?
|
?
Are you planning to "tuck-in" the steppers and use belt drive reduction to transmit stepper motion to the worms or are you going classic Losmandy style straight line with the stepper coupled directly to the worm?? Lots of options here.?
?
--
Chip Louie Chief Daydreamer Imagination Hardware?
Astrospheric Forecast - South Pasadena, CA?
?
?
?
|
I
had a very dusty dirt road about 20 feet from my G11.. For me, as ¡°closed¡± as
possible was preferable.. Landlord wanted to pave it, but I threw a fit about
that.. Didn¡¯t want a heat retaining piece of tarmac due west and close to my
scope.. Dust was preferable to bad seeing!
??? Ancient
history now.. City dweller and 3/4¡¯s blind..
Derek
?
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From: [email protected] [mailto:[email protected]] On Behalf Of John Kmetz via groups.io
Sent: Thursday, May 15, 2025 12:12
AM
To: [email protected]
Subject: Re: [Losmandy_users_io]
New (to me) older G11
?
On Wed, May 14, 2025 at 01:11 PM, Derek C Breit wrote:
I much prefer thrust washer, thrust bearing, thrust washer,
anodized donut, spring washer, and finally the clutch knob.
This allows the ¡°anodized donut¡± to help keep dust and dirt out of
the thrust bearings and provides an even load on the thrust washer..
Pretty sure this was the ¡°preferred¡± method from Winslow
astronomy.. Someone knows.. or can say I am crazy..
Derek
It will probably work that way as well, Derek, maybe even better I'm
just going by how it comes from the factory. User's choice.
_____________________________________________________________________________________________________________________________________________________________________________
Losmandy G11G2 on pier; refurbed Losmandy G11 with OnStep controller; SkyShed
design roll-off observatory; ZWO ASI2600MM-P; ZWO ASI071MC; Sky-Watcher Esprit
100 ED with field flattener; Celestron C925 Edge HD with 0.7XFR, William Optics
Zenithstar 61 APO; PHD2, NINA, Sequence Generator Pro and PixInsight user
|
On Wed, May 14, 2025 at 07:51 PM, Jesse Lichtenberg wrote:
<<< SNIPPED >>>
?
I'm glad to hear that nothing is missing in the photos and that the spacer rings are just undersized. I may pick up a set from Losmandy or perhaps just make something myself (or be fine with what I've got). Yes the polar scope was out at the time I took that photo - it is now back in place. I will likely remove it again and make a cap for it as I don't often use polar scopes anymore. I actually replaced the lens in the polar scope of my EQ6 with something a bit more suitable and made an adapter to mount a small mono sensor. Something like a Polemaster, I suppose, just for polar alignments. I may do the same with the G11.
?
Lots of good info here shared for the worm adjustments. I spoke a bit with Losmandy and while they didn't comment on the age of the mount it does seem a safe bet that it's of an older vintage. They did recommend a cleaning and relubrication. I have SuperLube on hand but will make sure it's the right stuff before I tear into things. I have to move about 800 miles away first. Hoping to start working on it in June.?
<<< SNIPPED? >>>
?
If you are going to be using a computer with your mount you will have no need for a polar scope.? So you can recoup a little money by selling it especially if it is in good condition and has the small silver illuminator and current reticle.? This will more than pay for replacement polar cap and regular sized thrust bearing spacers.??
?
The replacement polar scope cap is an all machined threaded alloy cap that is black anodized to match the mount.? You will not save anything by making your own and for what they charge for the right part.?
?
The SuperLube multi-purpose NLG1/2 with Syncolon (Teflon) should be the synthetic oil based grease, NOT the silicone based version!??
?
--
Chip Louie Chief Daydreamer Imagination Hardware?
Astrospheric Forecast - South Pasadena, CA?
?
?
?
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Lots more good information here - thank you again! I was turned to the bellows coupler as an option after reading the OnStep forums regarding other G11 installations. What I've purchased is pretty much exactly what they recommended, but I've no problem deviating from that if the system calls for it. More reading and research on my part is needed, and I'm grateful for the information and sources shared here!
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Re: Question about the G11T
The center of gravity (CoG) of the scope and accessories is closer to the RA center of rotation (CoR. Thus the counter weights and weight of weight shaft and its housing being farter from the CoR than the OTA &? etc. can be less than the payload. Multiply the object's distance from the datum (end of weight shaft here) by its weight to give you the movement for each object. Add up the movements of all the relevant objects. Here's some rough sentiments.
?
Mount 40"
Center of Mass 20"
OTA & etc. -- 70#
Cntr mass 33" from datum
Ctr wt. shaft 5#
Ctr mass 10"
Ctr wts. -- 50#
Ctr mass 3.75"
? ? ? ??
x =? M1*20+M2*37+M3*10 M4*3.75 =?
? ? ? ? ? ? M1+M2+M3? ? ? ? ? ? ? ? ? ? ? ?
40*20+70*33+5*10+50*3.75 = 6,527.5 = 20.3"
? ? ? ? ? ?40+70+5+50? ? ? ? ? ? ? ? ? ?165
?
So this comes up with a CoG of 20.3" from the datum selected, which was the end of the weight shaft. Note the two 25# weights are assumed to be at the lower end of the shaft. You may get better tracking by adding weight and moving their moment further up the shaft. I assumed that the mount's CoM was at the CoR.? It may be more like 60/40 top heavy when the weigh shaft is considered separately.
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On Wed, May 14, 2025 at 07:51 PM, Jesse Lichtenberg wrote:
Thank you for all the replies here, I very much appreciate the advice on where to head next. Double disc couplers were one I wasn't familiar with before. At the moment I have some bellows style stainless steel couplers I'd planned to use. They certainly weren't as cheap as some of the other options I could have gone with but were also nowhere near the cost of the double disc style from Ruland.
?
I most certainly have some work to do with the worms and I appreciate the information regarding R4 Belleville discs - that is something I've read a bit on and sounds like a sound way forward. Keeping them in alignment while setting backlash will be an adventure, but I've plenty of clamps and I can always pick up some angle aluminum as was mentioned here as well.?
?
I'm glad to hear that nothing is missing in the photos and that the spacer rings are just undersized. I may pick up a set from Losmandy or perhaps just make something myself (or be fine with what I've got). Yes the polar scope was out at the time I took that photo - it is now back in place. I will likely remove it again and make a cap for it as I don't often use polar scopes anymore. I actually replaced the lens in the polar scope of my EQ6 with something a bit more suitable and made an adapter to mount a small mono sensor. Something like a Polemaster, I suppose, just for polar alignments. I may do the same with the G11.
?
Lots of good info here shared for the worm adjustments. I spoke a bit with Losmandy and while they didn't comment on the age of the mount it does seem a safe bet that it's of an older vintage. They did recommend a cleaning and relubrication. I have SuperLube on hand but will make sure it's the right stuff before I tear into things. I have to move about 800 miles away first. Hoping to start working on it in June.?
?
John I will definitely reach out to see about a list of parts. That would be a huge help! I do think it would be worth my time to tear it all down and replace all I can. I have several bearing puller tools from prior projects so hopefully I can finish it with the tools on hand. And Derek I have seen several arguments back and forth regarding the 'proper' order ahead of the clutch knobs. I'll tackle that when I come to it!?
?
Jesse,
?
Coupler choice should be based on the mechanical needs of the coupler.? Unless you radically change the drive system the best choices are going to be an Oldham or a 2-disc type coupler and while Ruland are likely the best there are other good brands that cost less.? The ideal coupler for a power coupler driving a real time precision instrument will be a zero backlash constant velocity type even when misaligned, has no or very low buffering of torque, is low inertia and tolerant of some axial movement without screwing up everything else. This is a low speed application but all of this is important for this telescope mount drive coupler.? Don't pick a coupler based on what you have or price especially for this application, many issues have been caused by people using other types.? So do your research on couplers and look carefully at what is needed for this drive configuration to have no impact on power transmission.? Google the Ruland coupler comparison chart, it is very informative.?
?
The bearing blocks are an easy fix.? But if you look carefully there is a reason the original non-spring loaded $500 per axis Losmandy OPW was designed the way it was.? That design was optimized fully but cost $500 so a simpler version with a small design compromise was made and the cost difference was huge.? If you are going to go to the trouble of tying the worm bearing blocks together you might as well optimize the relationship between the worm block axis and whatever input drive you are going to use so you can choose the best coupler.? Think about it and look at the original Losmandy OPW design.?
?
Also think about the thin thrust bearings races having contact at only three small spots with the wavey washer.? This is an obvious assembly issue, the solution is to support the bearing races fully on both sides using the thick heavy spacer and placing the wavey spring between two much more solid surfaces of that thick spacer and the clutch adjustment knob that can carry that load smoothly.??
?
Regarding bearings, clean and inspect works for the major bearings so unless they are obviously damaged after cleaning they are probably fine.? The only bearings IME that should be replaced rather than cleaned and greased are the worm bearings.? They are cheap and you will never get them clean and lubed well enough to not have an impact on tracking.? This seems like a contributing source of low amplitude high frequency worm noise seen in tracking data.??
?
--
Chip Louie Chief Daydreamer Imagination Hardware?
Astrospheric Forecast - South Pasadena, CA?
?
?
?
|
On Wed, May 14, 2025 at 01:11 PM, Derek C Breit wrote:
I much prefer thrust washer, thrust bearing, thrust washer, anodized donut, spring washer, and finally the clutch knob.
This allows the ¡°anodized donut¡± to help keep dust and dirt out of the thrust bearings and provides an even load on the thrust washer..
Pretty sure this was the ¡°preferred¡± method from Winslow astronomy.. Someone knows.. or can say I am crazy..
Derek
It will probably work that way as well, Derek, maybe even better I'm just going by how it comes from the factory. User's choice.
?
John
--
_____________________________________________________________________________________________________________________________________________________________________________
Losmandy G11G2 on pier; refurbed Losmandy G11 with OnStep controller; SkyShed design roll-off observatory; ZWO ASI2600MM-P; ZWO ASI071MC; Sky-Watcher Esprit 100 ED with field flattener; Celestron C925 Edge HD with 0.7XFR, William Optics Zenithstar 61 APO; PHD2, NINA, Sequence Generator Pro and PixInsight user
|
Thank you for all the replies here, I very much appreciate the advice on where to head next. Double disc couplers were one I wasn't familiar with before. At the moment I have some bellows style stainless steel couplers I'd planned to use. They certainly weren't as cheap as some of the other options I could have gone with but were also nowhere near the cost of the double disc style from Ruland.
?
I most certainly have some work to do with the worms and I appreciate the information regarding R4 Belleville discs - that is something I've read a bit on and sounds like a sound way forward. Keeping them in alignment while setting backlash will be an adventure, but I've plenty of clamps and I can always pick up some angle aluminum as was mentioned here as well.?
?
I'm glad to hear that nothing is missing in the photos and that the spacer rings are just undersized. I may pick up a set from Losmandy or perhaps just make something myself (or be fine with what I've got). Yes the polar scope was out at the time I took that photo - it is now back in place. I will likely remove it again and make a cap for it as I don't often use polar scopes anymore. I actually replaced the lens in the polar scope of my EQ6 with something a bit more suitable and made an adapter to mount a small mono sensor. Something like a Polemaster, I suppose, just for polar alignments. I may do the same with the G11.
?
Lots of good info here shared for the worm adjustments. I spoke a bit with Losmandy and while they didn't comment on the age of the mount it does seem a safe bet that it's of an older vintage. They did recommend a cleaning and relubrication. I have SuperLube on hand but will make sure it's the right stuff before I tear into things. I have to move about 800 miles away first. Hoping to start working on it in June.?
?
John I will definitely reach out to see about a list of parts. That would be a huge help! I do think it would be worth my time to tear it all down and replace all I can. I have several bearing puller tools from prior projects so hopefully I can finish it with the tools on hand. And Derek I have seen several arguments back and forth regarding the 'proper' order ahead of the clutch knobs. I'll tackle that when I come to it!?
|
thrust washer, thrust bearing, thrust washer, spring washer, anodized
donut, and finally the clutch knob.
***
I
much prefer thrust
washer, thrust bearing, thrust washer, anodized donut, spring washer, and
finally the clutch knob.
This
allows the ¡°anodized donut¡± to help keep dust and dirt out of the thrust
bearings and provides an even load on the thrust washer..
Pretty
sure this was the ¡°preferred¡± method from Winslow astronomy.. Someone knows..
or can say I am crazy..
Derek
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Show quoted text
From: [email protected] [mailto:[email protected]] On Behalf Of John Kmetz via groups.io
Sent: Tuesday, May 13, 2025 7:12
PM
To: [email protected]
Subject: Re: [Losmandy_users_io]
New (to me) older G11
?
My second G11 is a refurbed 1997 era mount with the OnStep conversion.
Since yours is even older I would recommend replacing all bearings and thrust
washers, even the needle bearings inside. You will need a bearing puller to get
to these latter ones as it's near impossible to get any tool in behind them.
From the pics you are showing, I assume you are wanting to replace the lower
thrust washer assembly which goes in the following order - thrust washer,
thrust bearing, thrust washer, spring washer, anodized donut, and finally the
clutch knob. If you send me a PM I can give you a list of all the parts you
need and where to get them. I also can supply a lubricants sampler, with enough
original Losmandy greases to redo the mount.
There may be nothing wrong with the original stainless worms, which I
just reused on my mount. It all depends on their peak to peak error in
arcseconds; mine were around 10-12. Between using PPEC in PHD2 and Howard
Dutton's PEC correction tool, you get can your guiding errors down to pretty
low numbers. My worm connects directly to the motor via a bellows coupler, with
the right angle aluminum stock as already mentioned holding the motors in
place. But you should also do some type of Belleville washer upgrade on the far side
block to keep the bearings compressed and the 76s error to a minimum.?
Please let me know if I can help further.
_____________________________________________________________________________________________________________________________________________________________________________
Losmandy G11G2 on pier; refurbed Losmandy G11 with OnStep controller; SkyShed
design roll-off observatory; ZWO ASI2600MM-P; ZWO ASI071MC; Sky-Watcher Esprit
100 ED with field flattener; Celestron C925 Edge HD with 0.7XFR, William Optics
Zenithstar 61 APO; PHD2, NINA, Sequence Generator Pro and PixInsight user
|
On Tue, May 13, 2025 at 06:30 PM, Ray Gralak wrote:
The PEC ON log file shows that the mount's Declination was 89.9472, close to the celestial pole. This is a terrible place to measure periodic error, so the result with PEC ON is probably incorrect. You should run the calibration wizard with PEC enabled, which will offer to slew the scope to a good position in the sky.
Ray,? Once I clean and regrease the unit I will do another run and slew the mount again after the OFF run. I just ran the ON session straight after the initial OFF session without a slew - seems odd that it went that far.
?
I double checked the PHD2 calibration slew and the mount did a meridian flip when the small push north step ran at the end of it's slew - seems there is a mount limit in affect.
?
Thanks,
Ken
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On Tue, May 13, 2025 at 09:30 PM, Ray Gralak wrote:
The PEC ON log file shows that the mount's Declination was 89.9472, close to the celestial pole. This is a terrible place to measure periodic error, so the result with PEC ON is probably incorrect. You should run the calibration wizard with PEC enabled, which will offer to slew the scope to a good position in the sky.
?
Good catch, Ray! I didn't notice that in the logs, but for sure, that's the worst place to measure PE. Celestial equator near the meridian would be a much better start :)
?
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Hi Jesse,
?
My second G11 is a refurbed 1997 era mount with the OnStep conversion. Since yours is even older I would recommend replacing all bearings and thrust washers, even the needle bearings inside. You will need a bearing puller to get to these latter ones as it's near impossible to get any tool in behind them. From the pics you are showing, I assume you are wanting to replace the lower thrust washer assembly which goes in the following order - thrust washer, thrust bearing, thrust washer, spring washer, anodized donut, and finally the clutch knob. If you send me a PM I can give you a list of all the parts you need and where to get them. I also can supply a lubricants sampler, with enough original Losmandy greases to redo the mount.
?
There may be nothing wrong with the original stainless worms, which I just reused on my mount. It all depends on their peak to peak error in arcseconds; mine were around 10-12. Between using PPEC in PHD2 and Howard Dutton's PEC correction tool, you get can your guiding errors down to pretty low numbers. My worm connects directly to the motor via a bellows coupler, with the right angle aluminum stock as already mentioned holding the motors in place. But you should also do some type of Belleville washer upgrade on the far side block to keep the bearings compressed and the 76s error to a minimum.?
?
Please let me know if I can help further.
?
John
?
--
_____________________________________________________________________________________________________________________________________________________________________________
Losmandy G11G2 on pier; refurbed Losmandy G11 with OnStep controller; SkyShed design roll-off observatory; ZWO ASI2600MM-P; ZWO ASI071MC; Sky-Watcher Esprit 100 ED with field flattener; Celestron C925 Edge HD with 0.7XFR, William Optics Zenithstar 61 APO; PHD2, NINA, Sequence Generator Pro and PixInsight user
|
Hi Ken,
From your PEC ON log file:
# Declination # 89.9472
The PEC ON log file shows that the mount's Declination was 89.9472, close to the celestial pole. This is a terrible place to measure periodic error, so the result with PEC ON is probably incorrect. You should run the calibration wizard with PEC enabled, which will offer to slew the scope to a good position in the sky.
-Ray
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-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Oberon510 via groups.io
Sent: Sunday, May 11, 2025 10:42 AM
To: [email protected]
Subject: [Losmandy_users_io] PEC request
Hi,
I had cause to redo my G11G (with all latest firmware) PEC training and my OFF/ON PemPro logs seem to indicate
the PEC training was a success. The only problem is that my PHD2 Guiding Assistant logs (with tracking off)
show the periodic error is still there. I double checked PEC is enabled in the Gemini Telescope driver at startup.
Maybe I am reading something wrong so hoping someone could review the logs below for a second opinion.
There appears to be other things at play also but just hoping for an opinion on the PE work.
Thanks,
Ken
PS - BTW, how is the new Gemini PEC work progressing?
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Good Evening!
New to the group but not to Losmandy. I am looking into the G11T to mount my Meade 14 inch SCT (the non-ACF version) for both imaging and visual. I am going to guess around 70 pounds with all of the imaging and other accessories attached and with that number I am attempting to calculate the amount of counterweights that I need. I am figuring around 80 to 85 pounds (from my math) but another telescope site notes that all I need is 60% ( 45 pounds does not sound right) of the weight of the scope and accessories. Which number would be the closest to correct? This would help me decide how many extra counterweights to add to any future order. I have two 11 pound weights that I use with my current G11 (non-Gemini).
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One more: I would I need the MAL and the MAL to MA adapter to mount the G11T on the tripod that came with my G11? I do have the Meade Giant field tripod that came with the 14 inch. I do question the stability for imaging when compared to my Losmandy tripod.?
?
Thanks for the help!
?
Ken
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Re: DIY Spring Loaded Worms for the G11
Fantastic!! Thank you so much.?
?
What an awesome set of modifications
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Re: DIY Spring Loaded Worms for the G11
On Tue, May 13, 2025 at 12:41 AM, Avishek Aiyar wrote:
Looks like attachments and pictures disappear after a certain period of time.?
?
I would love to see the original attachments in these posts....is there a way to see them ??
?
This group has a limit of 1GB of photos and attachments storage. When folks upload new images or send large attachments (sometimes large movies!), older attachments are removed to make space for new ones. The only way to get around the 1GB limit is to convert this group to a paid group, which will require an annual payment to be collected and paid to Groups.io. The other alternative is to share large files through an external file sharing service, rather than sending them as attachments (dropbox, google drive, etc.)
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Re: DIY Spring Loaded Worms for the G11
Hi Avi -
Hmmm.? ?Yeah, I dont see the original images here either now.
I'm not sure Ive got everything duplicated at cloudy nights, but this should be enough to give you an idea:
https://www.cloudynights.com/topic/769071-losmandy-g11-onstep-conversion/?p=11116588
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Re: DIY Spring Loaded Worms for the G11
Looks like attachments and pictures disappear after a certain period of time.?
?
I would love to see the original attachments in these posts....is there a way to see them ??
?
Thanks!
?
Avi?
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Chip Louie
Paul Kanevsky