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DIY ET-8 GOTO Mount

astrophotography eq mount
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#151 Gary.McK

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Posted 08 March 2015 - 09:24 PM

Hi Howard,

 

my motors ar now slewing at 2.4 deg / sec, rotating smoothly and working well at 12 volts. I did a bit of experimenting with full and half step slewing, but you were dead accurate in saying that microstep slewing suppresses resonance. I got smoothest slewing using your suggested settings. Very happy camper now...

 

The programming part is a bit beyond me, I'm afraid, so I'll have to wait for someone to do it. It would be great if it was in Ascom like for example EQmod..., but until then I'm happy to use it as you designed it.....

 

cheers

Gary

 

 

 

 

 

Hi Howard,

 

thanks for the explanation - as a person with a biological background rather than an electronics one I'll take your word for it !!

 

It seems to be working fine, but the slewing speed is a little slow about 1/2 rev per second so I will need to play with settings to speed things up a bit to get to the 2 deg second target I'd like.

 

It would be nice if the ascom driver could handle the initialization - rather than needing your chart program or an android ap (I have a Windows phone!).... My old laptop is filled t the limit with Pinpoint, The Sky 6, Skytools 3, and Astroart.... It would be nice to avoid having to try to fit an extra charting program on to initialize the drive..... I have been using a borrowed android tablet to play....... but this must go back soon.

 

I'm also very appreciative of Steve for doing the boards, and you for doing the development work on the software.... Much applause from a non techie person here....

 

cheers

Gary

 

A MaxRate value of 32 is what I use to get 2.5 deg/sec. on my G11.

 

I'm not a big fan of ASCOM control panels cluttering up my screen, I like control in one application so that's what I did...

 

However, alignment of OnStep really needs just a few commands :A1# :A2# :A3# :A+# .  If using ASCOM's POTH a simple jscript or vbscript could be written to send the required commands (it would take just a few lines of code I believe.)

 

For example:

Use a script to start a two-star align, send ":A2#" using ASCOM's CommandBool().

Use your program of choice to goto a suitable star and center the star with guide commands.

Use a script accept the alignment star, send ":A+#" using ASCOM's CommandBool().

Use your program of choice to goto a suitable star and center the star with guide commands.

Use a script accept the alignment star, send ":A+#" using ASCOM's CommandBool().

Done.

 

Orly was wanting PEC control from ASCOM and this could be accomplished in a similar way.  I'll get around to throwing something together soon if no one else picks it up.  Perhaps a stand-alone windows application.

 

A jscript would look something like this (hacked jscript example provided with ASCOM install.)  Probably doesn't work, but it should be close:

------------------------------------

var H = new ActiveXObject("ASCOM.Utilities.Chooser");
// WScript.Echo("Pick driver in the Chooser. Then click Properties to activate its SetupDialog if required");

// Make chooser for Telescopes

H.DeviceType = "Telescope";

// I added "POTH Hub" below so drvrID is returned immediately

// if an empty string were passed it brings up the chooser dialog

var drvrID = H.Choose("POTH Hub");

if(drvrID === "") WScript.Quit(); // Cancelled chooser
var T = new ActiveXObject(drvrID); // Create instance of selected driver

// Start align one-star

var result=T.CommandBool(":A1#",true);

T = null;

H = null;

------------------------------------

 



#152 hjd1964

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Posted 09 March 2015 - 09:22 AM

 

Hi Howard,

 

my motors ar now slewing at 2.4 deg / sec, rotating smoothly and working well at 12 volts. I did a bit of experimenting with full and half step slewing, but you were dead accurate in saying that microstep slewing suppresses resonance. I got smoothest slewing using your suggested settings. Very happy camper now...

 

The programming part is a bit beyond me, I'm afraid, so I'll have to wait for someone to do it. It would be great if it was in Ascom like for example EQmod..., but until then I'm happy to use it as you designed it.....

 

cheers

Gary

 

Are the motors on the G11 yet?



#153 ssagerian

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Posted 09 March 2015 - 09:51 AM

Sounds like everyone is making progress, including yours truly, My friend John and I tested the LX50 conversion over the weekend and got the RA and DEC motors running. I need to button up everything, which I will do in the next day or two so that we can move on to validating the system as a whole. The next really important test is how well it tracks a star and to that end I wanted to ask how you measure that? I think I read some early measuring tracking performance it wasn't clear to me what tools or software was being used. Whats the process to measure the tracking performance, what tools do you use?

Thanks!

 

Steve



#154 hjd1964

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Posted 09 March 2015 - 01:07 PM

Sounds like everyone is making progress, including yours truly, My friend John and I tested the LX50 conversion over the weekend and got the RA and DEC motors running. I need to button up everything, which I will do in the next day or two so that we can move on to validating the system as a whole. The next really important test is how well it tracks a star and to that end I wanted to ask how you measure that? I think I read some early measuring tracking performance it wasn't clear to me what tools or software was being used. Whats the process to measure the tracking performance, what tools do you use?

Thanks!

 

Steve

 

Any luck getting my Android App and/or Sky Planetarium installed?

 

If you send me your Config.h file I can double-check to make sure everything looks like it's configured properly.

 

PHD2 is probably the tool you're interested in for evaluating tracking performance.



#155 photo444

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Posted 09 March 2015 - 01:10 PM

I was using a guider scope  and a ccd camera (cheap version http://www.cloudynig...ter-than-ln300/) with the MetaGuide which records all the tracking information.  I was analyzing the data to understand what was going on.  PHD2 will do the same thing I think.

 

I recently purchased Vixen SP mount whish is much better than what I have, ET-8.  I am slowly converting it to a GOTO mount with your board.

 

Paul


Edited by photo444, 09 March 2015 - 01:11 PM.


#156 pbunn

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Posted 09 March 2015 - 04:24 PM

I got the OnStep software installed and paired with the mount. Do you have another program available? (Sky Planetarium)

 

I also ordered a pair of Nema 11 motors from MPJA.

 

Going to the coast tomorrow so I'll probably wait til they arrive before doing anything else.

 

 

Pat



#157 photo444

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Posted 09 March 2015 - 07:44 PM

Pat,

 

Download it from the Stellajourney site.  I am enjoying it very much because it has nice features.

 

Paul



#158 Gary.McK

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Posted 09 March 2015 - 10:31 PM

Not yet - I have to make the brackets to mount them. You emailed me the dimensions a couple of months ago. Will be a couple of weeks before I get them up and running, but I will email you when they are go..

cheers

Gary


Are the motors on the G11 yet?

 

 



#159 Geo.

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Posted 11 March 2015 - 08:46 AM

A couple of ideas for SP motor mounts. I wouldn't try that fancy bend in the RA bracket. Better to make the dovetail a separate piece.

 

 

Attached Thumbnails

  • SP Bracket -RA.jpg
  • n_a.jpg


#160 Geo.

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Posted 11 March 2015 - 10:21 AM

The VEXTA 243 would be a nice motor  but I need a gearbox or I'll have to belt drive it and all that mounting will be a pain. I am lazy!

 

 

Pat

 

As is see it you have two problems with the GM8/G11. If you mount the drives as Losmandy does there's a problem with clash and the need for gear reduction. Using some Meade DS worms and crowns with the Vextra 18:1 motor you can mount the drive at a right angle to the worm for a lower profile and get an 18 * 60 = 1080:1 reduction to the worm or a 194400:1 final reduction with the 180 tooth crown.

 

 I have several of these worms and crowns that need employment.

 

Howard, currently I have the Uno R3 and want to experiment with that first. Which revision of OnStep do I want? TIA.


Edited by Geo., 11 March 2015 - 10:25 AM.


#161 orlyandico

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Posted 11 March 2015 - 12:07 PM

You don't need any further reduction on the 18:1 gearbox because the motor is micro-stepped at 1/16 or so. Hence 18 * 16 * 200 steps/rev = 57600 micro-steps per worm rotation. On the GM8 that gives you 0.125" per micro-step.

 

In fact the Atlas uses a 5:1 gearbox only.  And the piece de resistance: I've seen a web page where a G11 was direct-driven by a 400ppr stepper (no gearbox, stepper straight to the worm). With 400ppr and 1/16 micro-step, that's 0.56" per micro-step which is plenty.

 

One benefit of having no gearbox is, you have no gearbox periodic error! since most cheap gearboxes have around 2" to 4" p-p of error from the gearbox itself (the CGEM is a notable exception, as some of them - mine - had 25" p-p from the gearbox thanks to the 8/3).



#162 hjd1964

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Posted 11 March 2015 - 12:29 PM

You don't need any further reduction on the 18:1 gearbox because the motor is micro-stepped at 1/16 or so. Hence 18 * 16 * 200 steps/rev = 57600 micro-steps per worm rotation. On the GM8 that gives you 0.125" per micro-step.

 

In fact the Atlas uses a 5:1 gearbox only.  And the piece de resistance: I've seen a web page where a G11 was direct-driven by a 400ppr stepper (no gearbox, stepper straight to the worm). With 400ppr and 1/16 micro-step, that's 0.56" per micro-step which is plenty.

 

One benefit of having no gearbox is, you have no gearbox periodic error! since most cheap gearboxes have around 2" to 4" p-p of error from the gearbox itself (the CGEM is a notable exception, as some of them - mine - had 25" p-p from the gearbox thanks to the 8/3).

 

My G11 uses basically the same arrangement...  400 step Vexta motors in 32x micro-stepping mode driving the worms directly.  The tracking performance improvement was obvious over the 15:1 reduced 48 step tin-cans of my first goto setup.  And the cost of the motors was much less too.  This is what Gary.Mck is implementing.



#163 orlyandico

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Posted 11 March 2015 - 12:56 PM

Howard, I'm surprised you can slew the G11 with that direct-drive without full-stepping on the slew...!

 

The conventional wisdom always has been, the torque is so low at 1/16 or 1/32 that you won't be able to do high speed slews...



#164 hjd1964

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Posted 11 March 2015 - 01:33 PM

 

The VEXTA 243 would be a nice motor  but I need a gearbox or I'll have to belt drive it and all that mounting will be a pain. I am lazy!

 

 

Pat

 

As is see it you have two problems with the GM8/G11. If you mount the drives as Losmandy does there's a problem with clash and the need for gear reduction. Using some Meade DS worms and crowns with the Vextra 18:1 motor you can mount the drive at a right angle to the worm for a lower profile and get an 18 * 60 = 1080:1 reduction to the worm or a 194400:1 final reduction with the 180 tooth crown.

 

 I have several of these worms and crowns that need employment.

 

Howard, currently I have the Uno R3 and want to experiment with that first. Which revision of OnStep do I want? TIA.

 

 

As pointed out by Orly and tested by myself, the G11 is really simple to adapt.  The motors, thankfully, just clear everything they need to clear and don't stand-off much more than the stock ones.  Plus they're solid with the connecters orientated where no harm is done if it does bump one.

 

The GM8 is a bit of a problem due to it's 180 tooth worm-wheel:

 

The easiest way would be with a Hurst or similar tin-can, that's a drop-in for the stock digital drive motors.  These should be available as a 30:1 reduced 48 step motor unit that bolts right onto the mount.  Your goto speed would be 0.5 to 1°/sec or so.

 

The MPJA should be better and cheaper than the above solution.  I've seen others implement an arrangement where a motor is orientated similar to this:

motor1.jpg



#165 hjd1964

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Posted 11 March 2015 - 02:30 PM

Howard, I'm surprised you can slew the G11 with that direct-drive without full-stepping on the slew...!

 

The conventional wisdom always has been, the torque is so low at 1/16 or 1/32 that you won't be able to do high speed slews...

 

It's perfectly happy doing slews at 2.4 degrees per second (which is limited by my controller until I replace it with Steve's board.)  The 10" F/4 OTA is kind of light weight at just under 20 lbs by itself.  But I have a 5 lb camera in the focuser and a not at all light 80mm guide-scope etc. so it weighs a bit.

 

Reading up on the subject full-stepping vs. micro-stepping a little bit:

 

1. Standing still, full-step is more powerful.  2. In "slow" movement, up to 3 or 4 RPS (3-4 deg/sec for my G11) micro-stepping beats full stepping in torque; full stepping resonates and that wastes power.  3. Above this speed full-stepping rises to as much as about 20% more powerful.  4. Between 5 and 15 RPS more resonance trouble frequently happens (to both full and micro-stepped) that can again rob torque [edit: higher voltages/lower inductance push this toward the high end of that range]


Edited by hjd1964, 12 March 2015 - 02:49 PM.


#166 pbunn

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Posted 11 March 2015 - 04:21 PM

I have a few DS Motors myself and four LDX 55 motors.  I really don't want to introduce any more periodic error than I already have with the GM8.

 

I'll go with the Gemini system on the GM8 (I have one Gemini 2 on my G11) if there isn't a good way to couple this system to the GM8.

 

I was hoping to make the GM8 a decent lightweight  mount for AP that I can transport easier than my MyT. I'll probably mount the Gemini 2 on the GM 8 when I get it back from Losmandy and see how well that it works and if it does a decent job, move the 492 controller and steppers to the G11 and sell it. I'll have to buy a $30 conversion (crystal and new eeprom)

 

 

Pat



#167 ssagerian

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Posted 11 March 2015 - 04:23 PM

I just assumed you were kidding about the MyT..



#168 pbunn

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Posted 11 March 2015 - 06:09 PM

Nope - It is due in 5 weeks

 

I can't wait.

 

One Losmandy has to go.

 

Pat



#169 hjd1964

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Posted 11 March 2015 - 06:15 PM

 

The VEXTA 243 would be a nice motor  but I need a gearbox or I'll have to belt drive it and all that mounting will be a pain. I am lazy!

 

 

Pat

 

As is see it you have two problems with the GM8/G11. If you mount the drives as Losmandy does there's a problem with clash and the need for gear reduction. Using some Meade DS worms and crowns with the Vextra 18:1 motor you can mount the drive at a right angle to the worm for a lower profile and get an 18 * 60 = 1080:1 reduction to the worm or a 194400:1 final reduction with the 180 tooth crown.

 

 I have several of these worms and crowns that need employment.

 

Howard, currently I have the Uno R3 and want to experiment with that first. Which revision of OnStep do I want? TIA.

 

 

I started OnStep out on Arduino Uno Mega328 type hardware, but that's long ago left behind.  Flash is too small and the lack of enough hardware timers seriously limit it's performance.  It's the Teensy3.1 or Mega2560 only now, and I recommend the Mega2560 since the Teesny3.1 isn't as well tested.  A clone Mega2560 with a real crystal oscillator preferably.



#170 Geo.

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Posted 11 March 2015 - 07:52 PM

Got one for $12 delivered at http://www.gearbest.com/. Actually picked up two as smoke insurance. 



#171 hjd1964

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Posted 11 March 2015 - 08:24 PM

First test under the stars for my EM10 with the MPJA Vexta pk223pa-sg18 motors:

 

The first goto landed about 5 degrees off in Dec and near spot on in RA.  After a quick one-star align I went over to the owl nebula.  At more than twice the speed of the old motors this was painless.

 

Once PHD2 was calibrated I took a series of 30x30sec images of the owl with my DSLR. The serial shutter release was being troublesome so I was limited to 30s exposures.

 

My guide camera is a Lumenera LU070m attached to a 50mm finder.  This is the same setup as used to test OnStep earlier in this thread so you can compare before and after.  It's way better now.  I do realize that this isn't as demanding an area of the sky as nearer the celestial equator, but still:

 

TakEM10_Vexta.jpg


Edited by hjd1964, 11 March 2015 - 08:27 PM.


#172 Gary.McK

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Posted 14 March 2015 - 09:44 PM

Hi Howard,

 

ended up making my mounting brackets more quickly than anticipated, so now have everything ready to mount on the G11.

 

I am doing a test of my ST8300 vs my Nikon D7000 with the current Gemini G1 drive. When this is complete I will do a Pempro run with the  Gemini 1 drive to characterise it, and then fit the Onstep steppers and do another Pempro run without altering anything except the drive motors. I'll post the results here. I am sort of anticipating that the direct drive of the worm by Onstep and the 400 step steppers will result in a much smoother tracking result than the geared down servo motors (elimation of gear "noise"), but we shall see!!

 

cheers

Gary

 

 

 

Not yet - I have to make the brackets to mount them. You emailed me the dimensions a couple of months ago. Will be a couple of weeks before I get them up and running, but I will email you when they are go..

cheers

Gary


Are the motors on the G11 yet?

 

 

 



#173 photo444

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Posted 16 March 2015 - 07:28 AM

I recently purchased a used Vixen SP which is in very good shape.  I have finished mounting two Nema 17 400steps/rev with home made brackets.  I am now waiting for the belts to come in my mailbox. With Steve's board I soon be running GOTO.  I always have been fighting reducing the payload of ET-8 but no more!  Vixen SP is much nicer than ET-8.

 

Paul



#174 ssagerian

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Posted 16 March 2015 - 08:47 AM

Paul,

thanks, however, Howard is the Genius behind the board design. I took his initial design and (working with Howard) created a common platform for all us to experiment with, develop new features, explore different motor combiniations/configurations,  find and fix bugs etc.   I really think it was Howard's clever way of getting some free software testers...

 

Steve



#175 photo444

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Posted 16 March 2015 - 09:20 AM

Steve,

 

I know, I know,..  We are deeply indebted to Howard for is endeavor.  Without him all was not possible.  I have been writing a software for myself and gave up immediately when I saw Stellajourney/OnStep.  This forum was started to shine some light to his work.  I am glad and happy many are enjoying and achieving Howard's work and your board.:)

 

Paul




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