rsbfoto
sage
Reged: 06/10/06
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New ? Stepper focuser
#5499304 - 11/01/12 12:02 PM
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Hi,
Maybe this is an old info but did not find anything about this here doing a search.
Lokos like there is a new player in the market.
Anybody knows or has a focuser from this company ?
www.usb-foc.us
I am asking because a friend in Mexico found it and we wrote to them a few e-mails but got no answer so far.
Sorry if this was already mentioned here.
Thanks and regards Rainer
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korborh
professor emeritus
Reged: 01/29/11
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Re: New ? Stepper focuser
[Re: rsbfoto]
#5500035 - 11/01/12 10:05 PM
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I am waiting on reviews for this one. Its great to see a stepper focusing solution that is not outrageously priced. Everything else currently is. I hope this thing works well.
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Raginar
Carpal Tunnel
Reged: 10/19/10
Loc: Rapid CIty, SD
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Re: New ? Stepper focuser
[Re: korborh]
#5500043 - 11/01/12 10:09 PM
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I got an email back. They sounded super helpful. My only issues is not being able to give them the actual measurements to create the adapters needed to fit their focuser to my focuser.
Give it a few days, they're in France I believe.
Chris
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rigelsys
Vendor (Rigel Systems)
Reged: 08/22/06
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Re: New ? Stepper focuser
[Re: Raginar]
#5500180 - 11/01/12 11:39 PM
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Hard to believe they can get enough juice from usb to drive a stepper with any kind of torque and without sucking the PC dry :-)
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korborh
professor emeritus
Reged: 01/29/11
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Re: New ? Stepper focuser
[Re: rigelsys]
#5500277 - 11/02/12 12:57 AM
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Quote:
Hard to believe they can get enough juice from usb to drive a stepper with any kind of torque and without sucking the PC dry :-)
2.5W from USB + reduction gears. Seems quite feasible.
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Phil Sherman
Pooh-Bah
Reged: 12/07/10
Loc: Cleveland, Ohio
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Re: New ? Stepper focuser
[Re: korborh]
#5500654 - 11/02/12 10:16 AM
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I hope they're not using reduction gears. The purpose of a stepper motor drive for a focuser, particularly a Crayford, is to allow absolute positioning of the focuser. Any gears between the stepper motor and the focuser will introduce backlash unless you use the special anti-backlash gearing systems that have been around for about a century. Unfortunately these systems have very little torque capability because they're spring loaded.
The Crayford focuser itself should give a good deal of reduction. If you have a dual speed, and you hook the stepper to the reducer knob, then you'll also get a torque multiplier from the reducer's planetary gear reduction. Most of these don't use gears but use rotating shafts which, like the Crayford itself, have no backlash.
Phil
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rigelsys
Vendor (Rigel Systems)
Reged: 08/22/06
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Re: New ? Stepper focuser
[Re: Phil Sherman]
#5501021 - 11/02/12 02:01 PM
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Big pear shaped gear box underneath round stepper motor is for the reduction gears. Sorry, steppers can't get down to 0.1 deg/step or so, without gears
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bassplayer142
professor emeritus
Reged: 10/03/11
Loc: Michigan
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Re: New ? Stepper focuser
[Re: Phil Sherman]
#5501033 - 11/02/12 02:13 PM
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I don't see why lash would even be an issue. Gearing a stepper down, if anything, creates a higher resolution due to smaller step sizes. Plus the additional torque helps with heavier ep's.
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rigelsys
Vendor (Rigel Systems)
Reged: 08/22/06
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Re: New ? Stepper focuser
[Re: bassplayer142]
#5501044 - 11/02/12 02:22 PM
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Gearing creates backlash, when changing direction gears load from one side of the teeth to the other side before they start turning. Usually amounts to a few steps required after changing direction before focuser starts moving.
Quote:
I don't see why lash would even be an issue. Gearing a stepper down, if anything, creates a higher resolution due to smaller step sizes. Plus the additional torque helps with heavier ep's.
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rigelsys
Vendor (Rigel Systems)
Reged: 08/22/06
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Re: New ? Stepper focuser
[Re: korborh]
#5501259 - 11/02/12 05:19 PM
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Most steppers are run at 12V (higher voltages, more torque) so if 2.5W at 5V is boosted to 12V, that's about 1A which just about matches what a stepper will pull when making a step if its lifting a significant load. So when the stepper steps, expect the lights to dim for all the other usb devices plugged into the PC 
Also when the stepper completes a step can expect some voltage feedback into the box which if not filtered properly can feed back into the usb port and PC.
Quote:
Quote:
Hard to believe they can get enough juice from usb to drive a stepper with any kind of torque and without sucking the PC dry :-)
2.5W from USB + reduction gears. Seems quite feasible.
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korborh
professor emeritus
Reged: 01/29/11
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Re: New ? Stepper focuser
[Re: rigelsys]
#5501441 - 11/02/12 07:33 PM
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What I am trying to say is 500mA at 5V with torque boost from reduction gears ought to be enough to move most focusers....not a lot of power is needed. Also the reverse voltage kick from the stepper is quite simple to filter/clamp out.
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bassplayer142
professor emeritus
Reged: 10/03/11
Loc: Michigan
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Re: New ? Stepper focuser
[Re: rigelsys]
#5509945 - 11/08/12 01:05 PM
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I only see this being a problem if you go just past focus and come backwards to re-find focus, but shoot over due to lash.
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korborh
professor emeritus
Reged: 01/29/11
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Re: New ? Stepper focuser
[Re: bassplayer142]
#5509995 - 11/08/12 01:42 PM
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Most autofocus software can be setup to focus only in one direction, so backlash is non-issue.
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averen
Vendor Main Sequence Software
Reged: 01/20/09
Loc: Austin TX
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Re: New ? Stepper focuser
[Re: korborh]
#5515330 - 11/12/12 12:07 AM
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I made a focuser driver that powers the stepper directly off of USB a while back. It's worked great for about a year now. No issues what so ever. I've ran it directly off of the PC as well as a hub (how it's normally connected). I've powered a MicroTouch motor as well as a Moonlite motor and both have performed well.
The main benefit is that I can microstep (the MicroTouch has a lot of vibration if I don't microstep it). I've never had any power issues even when lifting my Qhy9 + Filterwheel.
The steppers are geared and as such don't draw a ton of power. I use a boost converter to push the 5V up to 12V. Never had any issues with it. I did some tests a while back to see if I could draw enough power to cause problems with my laptop. With the crayford it ended up slipping, the AP130 is a rack and pinion and the stepper ended up missing some steps when jammed but the PC had no problems powering it. I didn't check the amperage that it was pulling.
Also with regards to gear slop...most gear boxes for steppers are pretty tight. You won't get more than a few microns movement on the tube side. That will still put you in critical focus. There are very few focusers out there that employ a direct stepper connection. Even at 200 steps/rev that's not enough resolution to put most scopes within the critical zone. Thus reduction is required. I've never had issues with a reduced stepper motor configuration.
Jared
Edited by averen (11/12/12 12:11 AM)
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wasyoungonce
sage
Reged: 06/07/07
Loc: Land Downunder
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Re: New ? Stepper focuser
[Re: averen]
#5515427 - 11/12/12 01:35 AM
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Probably a little left field...I purchased a very cheap focuser Stepper controller kit (SharpSky controller) from Dave Trewen, in England.
He is a software/hardware engineer..Use your own stepper (he does have some) or use something like a Moonlite stepper (or robo focuser).
Dave's kit is fully ASCOM compliant, works with all the major focus control systems.
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USB_Focus
Vendor- USB_Focus
Reged: 11/13/12
Loc: France
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Re: New ? Stepper focuser
[Re: wasyoungonce]
#5519056 - 11/14/12 04:25 AM
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Hi all
I am designer and reseller of the product USB_Focus (www.usb-foc.us)
If you have any question feel free to contact me.
Best regards
Vincent
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rsbfoto
sage
Reged: 06/10/06
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Re: New ? Stepper focuser
[Re: USB_Focus]
#5524314 - 11/17/12 12:46 PM
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Hi Guys,
Thank You all for the interesting asnwers even if it drifted away from the original question 
Edited by rsbfoto (11/17/12 12:47 PM)
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weikinger
newbie
Reged: 10/03/11
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Re: New ? Stepper focuser
[Re: rsbfoto]
#5531611 - 11/21/12 07:29 AM
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Bonjour Vincent!
I am just considering a new setup and indeed have a few questions regarding usb_focus, which might be of general intrest too:
1) Do you offer or plan to offer mounting brackets for moonlite and baader steeltrack focusers?
2) As the focuser motor is connected to the focuser shaft via a gearbox the question of backlash arises. Do you have any practical experience on backlash issues? Is the backlash compensation feature in FocusMax necessary and sufficient for solving such issues, if any?
3) Have you made any experience with the focus motor connected via a usb hub an not directly to a free usb slot of the PC?
4) Is ist possible to still move the focuer mannually although having the focus motor installed?
5) Is it possible to get the cable connection between the handbox and the motor in a longer version (seems to be < 50 cm from your product images)?
Excusez moi for my denglish (my French is even worse) and many thanks in advance for any answers on the above.
Best and CS
Simon
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USB_Focus
Vendor- USB_Focus
Reged: 11/13/12
Loc: France
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Re: New ? Stepper focuser
[Re: weikinger]
#5534128 - 11/22/12 03:55 PM
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Hi Simon, all
to answer your questions :
1/ Yes brackets available moonlite and baader steeltrack focusers
2/ several experienced customers and I found same backlash, around 58 half-steps. Focusmax is perfect for this job.
3/ provided USB-HUB is self powered, it is no problem. If not, take care to others peripherals attached.
4/ Yes it is possible to move focuser manually as motor attached. You need to unscrew the coupler a little.
5/ Yes a direct DB9 male to female can extend the motor to controller length.
I hope this helps.
Best regards
Vincent
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korborh
professor emeritus
Reged: 01/29/11
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Re: New ? Stepper focuser
[Re: USB_Focus]
#5675059 - 02/12/13 12:27 AM
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Bumping this thread - anybody tried the usb-foc.us and have reviews/opinions on reliability, repeat-ability, ease of use etc.? 
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