Newbie- help me understand the basics here


W Maxwell
 

I have a losmandy gm8 withe the 492 controller, stock motors, and a gpusb for autoguiding. 

Would the Onstep replace the 492 box AND the GPusb?  Could onstep usb into a laptop and both send guide pulses via PHD2 and move the mount via a planetarium program (not at the same time obviously).

Is the main advantage of replacing the stock motors slew speed? Would the stock motors work, just be "painfully slow" or is there a reason why only certain motors can be used?

Once I have the onstep hardware built, what do I need to know to get it properly synced up with the mount/motors?

Would all of these basic answers apply if I was to also add an onstep to a CG-4 mount, just adjusting for the specifics, like motors and gear ratios, for that mount? Is the basic onstep universal, just  "programmed" for each mount?

Thanks for any info. I'm almost there, just have too many variables to  fully grasp the concept.

-William


JoAnn
 

On Tue, Sep 29, 2020 at 03:36 AM, <williambass5@...> wrote:
I have a losmandy gm8 withe the 492 controller, stock motors, and a gpusb for autoguiding. 

Would the Onstep replace the 492 box AND the GPusb?  Could onstep usb into a laptop and both send guide pulses via PHD2 and move the mount via a planetarium program (not at the same time obviously).

Is the main advantage of replacing the stock motors slew speed? Would the stock motors work, just be "painfully slow" or is there a reason why only certain motors can be used?

Once I have the onstep hardware built, what do I need to know to get it properly synced up with the mount/motors?

Would all of these basic answers apply if I was to also add an onstep to a CG-4 mount, just adjusting for the specifics, like motors and gear ratios, for that mount? Is the basic onstep universal, just  "programmed" for each mount?

Thanks for any info. I'm almost there, just have too many variables to  fully grasp the concept.

-William
I just finished my GM8. I just have the RA base but would be the same info for DEC as well. You can use the stock motors. They are 24 step motors with 150 gear reduction. the onstep controller would connect to your guiding program via ascom (or st4 cable if you went that route). I don't use it for GOTO because , yes, it is WAY too slow. I used the Wemos R32/cnc shield to build mine. 
My main use is solar so I just point to the sun. As a camera tracker, I would aim manually, platesolve, and the slew the small distance to target. 

Once built, you would connect to ASCOM software like any other mount. There is an app or webserver to get initialized. Howard has a nice planetarium program that has many features. 

When programming OnStep using Arduino, you have to enter certain values based on your mount specifics like worm wheel teeth, gear reduction etc but there is a excel sheet for that. 

The main troubles with the GM8 in replacing motors is trying to add some reduction to the imaging train. You have to find a coupler that is small enough in diameter to replace the current coupler or have a way to turn down the standard 19/20mm diameter flexible coupler. Also, for imaging, you really need more gear reduction than simply attaching the NEMA motor directly to the worm. 3/1 would be minimum. You can get nema motors with a planetary gear head but I am not sure how bad the backlash would be, plus they stick way out and are heavy. 

see my build pics here: https://photos.app.goo.gl/ziBjWwY3BFbEhXAv5

JoAnn


W Maxwell
 

Thank you. Most helpful.

Just so I am clear: The WemosR32 does what the GPusb is now doing in mine? If so, is there a way to just use the GPusb that I have?


JoAnn
 

On Tue, Sep 29, 2020 at 03:36 AM, <williambass5@...> wrote:
Could onstep usb into a laptop and both send guide pulses via PHD2 and move the mount via a planetarium program (not at the same time obviously).
you would not use the GPusb if doing pulse guiding. You mount (Onstep) and guide camera would have to be connected to PHD2. You could add an ST4 port for use with a hand controller. 


Khalid Baheyeldin
 

On Tue, Sep 29, 2020 at 06:36 AM, <williambass5@...> wrote:
Would the Onstep replace the 492 box AND the GPusb? 
Yes and Yes.

And if you want, you don't need an ST4 port with OnStep, since ASCOM (or INDI) can be used to send the pulses directly to the mount without an intervening ST4.

Could onstep usb into a laptop and both send guide pulses via PHD2 and move the mount via a planetarium program (not at the same time obviously).
Yes to all.

Is the main advantage of replacing the stock motors slew speed?
Yes. Depending on how you connect the new motors, there may be precision advantages as well (e.g. very little backlash, and predictable periodic error).

Would the stock motors work, just be "painfully slow" or is there a reason why only certain motors can be used?
It is a balance/trade-off between a sufficiently high overall reduction rate (to get down to a good resolution), but not too much reduction so as to not be fast enough in slewing.

Once I have the onstep hardware built, what do I need to know to get it properly synced up with the mount/motors?
You need to know:
- The steps per degree for the motors (usually 200 or 400).
- Their maximum current for the motors.
- The gear ratio between the motor and the worm gear (pulley ratio, or 1:1 if directly coupled).

Those values are entered in a spreadsheet (see the Construction page on the Wiki), and it calculates the numbers needed.

Would all of these basic answers apply if I was to also add an onstep to a CG-4 mount,
Yes.
The mechanical part would be different (pulley sizes, ...etc)
But the electronic part is the same.

just adjusting for the specifics, like motors and gear ratios, for that mount? Is the basic onstep universal, just  "programmed" for each mount?
If you have a controller, it works with any mount that has steppers, provided the drivers can output enough current for the motors (if those are different). So yes, it is a matter of reprogramming.


"Guilherme Vênere
 

Hi

I had your exact same setup a few weeks ago before replacing it with OnStep. My GM8 used the 492 controller with stock motors and hand controller, and now I control everything via OnStep. I replaced the motors with a 400 step/degree Nema17, and it is connected directly to the gear worm without any reduction, and it works great for astrophotography. Just see the attached image which was the first one I did after the conversion. 

As for controlling the mount there are several options. You can control it via USB serial, or via IP connection. My choice was to have everything done via IP. My OnStep joins my home WiFi and I connect Stellarium for planetarium software, N.I.N.A to control the mount and my camera gear, and PHD2 for guiding. All of that is using the ASCOM driver for OnStep connected via IP.

I can also control the mount via my iPhone, either directly via the web page served by OnStep, or by the gotomote app, or via Redshift Pro planetarium

There's no point in using the GPUSB after installing OnStep. It would just add more complexity as you would need to add an ST4 port to OnStep, and connect your GPUSB there and have your computer+gpusb  do the work that OnStep should be doing

Guilherme


119963117_3701688983198544_3210251431978618042_o.jpg
120069108_3701688906531885_2507810754929714904_o.jpg
119641451_3701689039865205_3330260693539259337_o.jpg

On Tue, Sep 29, 2020 at 9:23 AM Khalid Baheyeldin <kbahey@...> wrote:
On Tue, Sep 29, 2020 at 06:36 AM, <williambass5@...> wrote:
Would the Onstep replace the 492 box AND the GPusb? 
Yes and Yes.

And if you want, you don't need an ST4 port with OnStep, since ASCOM (or INDI) can be used to send the pulses directly to the mount without an intervening ST4.

Could onstep usb into a laptop and both send guide pulses via PHD2 and move the mount via a planetarium program (not at the same time obviously).
Yes to all.

Is the main advantage of replacing the stock motors slew speed?
Yes. Depending on how you connect the new motors, there may be precision advantages as well (e.g. very little backlash, and predictable periodic error).

Would the stock motors work, just be "painfully slow" or is there a reason why only certain motors can be used?
It is a balance/trade-off between a sufficiently high overall reduction rate (to get down to a good resolution), but not too much reduction so as to not be fast enough in slewing.

Once I have the onstep hardware built, what do I need to know to get it properly synced up with the mount/motors?
You need to know:
- The steps per degree for the motors (usually 200 or 400).
- Their maximum current for the motors.
- The gear ratio between the motor and the worm gear (pulley ratio, or 1:1 if directly coupled).

Those values are entered in a spreadsheet (see the Construction page on the Wiki), and it calculates the numbers needed.

Would all of these basic answers apply if I was to also add an onstep to a CG-4 mount,
Yes.
The mechanical part would be different (pulley sizes, ...etc)
But the electronic part is the same.

just adjusting for the specifics, like motors and gear ratios, for that mount? Is the basic onstep universal, just  "programmed" for each mount?
If you have a controller, it works with any mount that has steppers, provided the drivers can output enough current for the motors (if those are different). So yes, it is a matter of reprogramming.


Khalid Baheyeldin
 

Guilherme,

Thank you for sharing the pictures. I added your mount to the Showcase page.


W Maxwell
 

Thank you all. Superb and very helpful replies.


W Maxwell
 

On Tue, Sep 29, 2020 at 09:39 AM, "Guilherme Vênere wrote:
Nema17
Are those the Nema 17 motors that are about $13 each? Did it take any special adaptation to attach them to your GM8? Probably a really basic question, but does "bipolar" on a motor mean "reversible?

The outcome looks great on your mount and bravo on the image as well.


"Guilherme Vênere
 

Hello

As you may have noticed from my pictures I use a premade box from Instein.eu. The motors and supports came with the kit so i didn't really have much to do there as it comes adjusted for the GM8. 

The motors are these: 17HM15-0904S 

They come with a support plate that is screwed directly to the worm support plate and use a flexible coupling to attach to the worm instead of the oldham coupler

Guilherme

On Tue, Sep 29, 2020 at 1:03 PM williambass5 via groups.io <williambass5=yahoo.com@groups.io> wrote:
On Tue, Sep 29, 2020 at 09:39 AM, "Guilherme Vênere wrote:
Nema17
Are those the Nema 17 motors that are about $13 each? Did it take any special adaptation to attach them to your GM8? Probably a really basic question, but does "bipolar" on a motor mean "reversible?

The outcome looks great on your mount and bravo on the image as well.


W Maxwell
 

also,  Guilherme, (since you had what was my exact setup and I could end up with your current exact setup):
What were these values on the motors/onstep/gm8 you used?


- The steps per degree for the motors (usually 200 or 400).
- Their maximum current for the motors.
- The gear ratio I assume is 1:1?

So, to state the obvious, and what appears to have been the original motivation from the originator of the project, its possible to get a, functionally speaking, Gemini setup (although a laptop is needed) on a losmandy mount for about $100?? Crazy. I don't think you can buy a losmandy rubber foot for that...Not to disparage the brand, great engineering, love mine, but rather exciting that a goto system is within reach of us mortals. Kudos to the original designer and for making it public.


Dave Schwartz
 

And 'bipolar' just means that the motors are designed for drivers that run current through the coils in either direction. You will also see 'unipolar' which supports designs from the stone age where drivers were implemented with discrete components and the design was much simpler if you never reversed the current (just went from zero to the maximum in one of the directions). The most common 'Unipolar' motors had center-tapped coils where one half of the coil was for current in one direction and the other half for the other direction. You can use unipolar motors in bipolar mode by either ignoring one half of the coil or ignoring the center tap (generally ignoring one half of the coil is preferred).

All steppers are reversible... they run in a direction according to the relative directions of the current in the coils.

On 2020-09-29 4:17 p.m., "Guilherme Vênere wrote:
Hello

As you may have noticed from my pictures I use a premade box from Instein.eu. The motors and supports came with the kit so i didn't really have much to do there as it comes adjusted for the GM8.

The motors are these: 17HM15-0904S
https://www.omc-stepperonline.com/nema-17-bipolar-0-9deg-36ncm-51oz-in-0-9a-5-4v-42x42x40mm-4-wires.html

They come with a support plate that is screwed directly to the worm support plate and use a flexible coupling to attach to the worm instead of the oldham coupler

Guilherme

On Tue, Sep 29, 2020 at 1:03 PM williambass5 via groups.io <http://groups.io> <williambass5=yahoo.com@groups.io <mailto:yahoo.com@groups.io>> wrote:

On Tue, Sep 29, 2020 at 09:39 AM, "Guilherme Vênere wrote:

Nema17

Are those the Nema 17 motors that are about $13 each? Did it take
any special adaptation to attach them to your GM8? Probably a
really basic question, but does "bipolar" on a motor mean "reversible?

The outcome looks great on your mount and bravo on the image as well.


Henk Aling
 

You are getting some good advice here.  Let's assume you are now convinced that the GPusb is no longer needed and that you will get different stepper motors.

The Instein deal is hard to beat if you want minimum hassle and a nicely finished product.   If you just want the cheapest way to cobble something together with just the motors working (the most important part), I can recommend the Wemos R32 / CNCv3 shield.  You can basically just plug the boards together, for mode switching with SPI (different step rates for slewing and tracking) you need to plug in some female/female connectors.

Here are pictures of my setup: https://onstep.groups.io/g/main/message/25542 .  Note that I put a Raspberry Pi 2B right next to it, I use it for running Ekos/Kstars for controlling OnStep, autoguiding, planetarium control, etcetera, remotely logged in through VNC.  It is a Linux based alternative to Ascom that is quite powerful.  There are others using it too.  The Pi only uses 2W or so, as opposed to a power hungry laptop.  I have no Wifi but Bluetooth works great with the OnStep Android app.  I use that app for alignment.  The RJ45 connectors are big and ugly but it looks like a piece of (preschool) art.  It works great.


"Guilherme Vênere
 

William

Some of these questions will depend only on the components you choose to assemble your OnStep. 

- The steps per degree for the motors (usually 200 or 400). 
==> This comes from the motor you choose. The one i mentioned before has 400 steps/degree and is enough to allow good tracking even for astrophotography

- Their maximum current for the motors.
==> These parameters depend on the motor itself, and the type of controller you use. The motor I recommended hyas max current at 0.9A. The Instein box I have uses the TMC2130 driver, which is configured via SPI by OnStep. That means i have all my current limiting set to OFF in the config.h

- The gear ratio I assume is 1:1? 
==> That would be true for the first gear ratio needed by the OnStep Configuration tool (http://o.baheyeldin.com:1111/). The Losmandy GM8 have 180 teeth in the worm gear, and i used that value as the second ratio (GR2). I also used 64 microsteps for tracking/goto. In the end, my configuration for the motors look like that:

image.png

which translates to: 

// AXIS1 RA/AZM
// see https://onstep.groups.io/g/main/wiki/6-Configuration#AXIS1
#define AXIS1_STEPS_PER_DEGREE     12800.0 //  12800, n. Number of steps per degree:                                          <-Req'd
                                          //         n = (stepper_steps * micro_steps * overall_gear_reduction)/360.0
#define AXIS1_STEPS_PER_WORMROT   25600 //  12800, n. Number of steps per worm rotation (PEC Eq mode only:)                <-Req'd
                                          //         n = (AXIS1_STEPS_PER_DEGREE*360)/reduction_final_stage

#define AXIS1_DRIVER_MODEL            TMC2130_QUIET //    OFF, (See above.) Stepper driver model.                                      <-Often
#define AXIS1_DRIVER_MICROSTEPS       64 //    OFF, n. Microstep mode when tracking.                                        <-Often
#define AXIS1_DRIVER_MICROSTEPS_GOTO  OFF //    OFF, n. Microstep mode used during gotos.                                     Option
#define AXIS1_DRIVER_IHOLD            OFF //    OFF, n, (mA.) Current during standstill. OFF uses IRUN/2.0                    Option
#define AXIS1_DRIVER_IRUN             OFF //    OFF, n, (mA.) Current during tracking, appropriate for stepper/driver/etc.    Option
#define AXIS1_DRIVER_IGOTO            OFF //    OFF, n, (mA.) Current during slews. OFF uses same as IRUN.                    Option
#define AXIS1_DRIVER_REVERSE          OFF //    OFF, ON Reverses movement direction, or reverse wiring instead to correct.   <-Often
#define AXIS1_DRIVER_STATUS           OFF //    OFF, TMC_SPI, HIGH, or LOW.  Polling for driver status info/fault detection.  Option

#define AXIS1_LIMIT_UNDER_POLE        180 //    180, n. Where n=150..180 (degrees.) Max HA hour angle + or - for Eq modes.    Adjust
#define AXIS1_LIMIT_MAXAZM            360 //    360, n. Where n=180..360 (degrees.) Max Azimuth + or - for AltAzm mode only.  Adjust

But again, these are specific to the box i use (well, GM8 worm gear teeth is standard) so you need to define a few things before looking at these values

Guilherme


 


On Tue, Sep 29, 2020 at 2:05 PM Henk Aling <haling@...> wrote:
You are getting some good advice here.  Let's assume you are now convinced that the GPusb is no longer needed and that you will get different stepper motors.

The Instein deal is hard to beat if you want minimum hassle and a nicely finished product.   If you just want the cheapest way to cobble something together with just the motors working (the most important part), I can recommend the Wemos R32 / CNCv3 shield.  You can basically just plug the boards together, for mode switching with SPI (different step rates for slewing and tracking) you need to plug in some female/female connectors.

Here are pictures of my setup: https://onstep.groups.io/g/main/message/25542 .  Note that I put a Raspberry Pi 2B right next to it, I use it for running Ekos/Kstars for controlling OnStep, autoguiding, planetarium control, etcetera, remotely logged in through VNC.  It is a Linux based alternative to Ascom that is quite powerful.  There are others using it too.  The Pi only uses 2W or so, as opposed to a power hungry laptop.  I have no Wifi but Bluetooth works great with the OnStep Android app.  I use that app for alignment.  The RJ45 connectors are big and ugly but it looks like a piece of (preschool) art.  It works great.


Khalid Baheyeldin
 

On Tue, Sep 29, 2020 at 04:20 PM, <williambass5@...> wrote:
So, to state the obvious, and what appears to have been the original motivation from the originator of the project, its possible to get a, functionally speaking, Gemini setup (although a laptop is needed) on a losmandy mount for about $100?? Crazy. I don't think you can buy a losmandy rubber foot for that...Not to disparage the brand, great engineering, love mine, but rather exciting that a goto system is within reach of us mortals. Kudos to the original designer and for making it public.
Yes, we are all grateful to Howard Dutton for creating and sharing OnStep with the world ...

By the way, most companies that sell mounts do not develop the controllers firmware in-house at all.
For example, the Gemini system for Losmandy was developed by Rene Goerlich.
And that is why they don't continue to improve it at the same pace that OnStep does ...


Dave Schwartz
 

Same thing for Meade. AutoStar software development was outsourced and I don't think they have the expertise to modify the code very much themselves (and may not even have access to the original developer). That's why Meade only releases the most basic updates despite some glaring bugs that have existed for a very long time. The best code support comes from two chaps who have reverse engineered the machine code to patch it and even add new features (although at only about 1/1000th the rate of OnStep and in a way that only someone from the 1960s would understand).

On 2020-09-29 5:48 p.m., Khalid Baheyeldin wrote:
On Tue, Sep 29, 2020 at 04:20 PM, <williambass5@yahoo.com> wrote:

So, to state the obvious, and what appears to have been the
original motivation from the originator of the project, its
possible to get a, functionally speaking, Gemini setup (although a
laptop is needed) on a losmandy mount for about $100?? Crazy. I
don't think you can buy a losmandy rubber foot for that...Not to
disparage the brand, great engineering, love mine, but rather
exciting that a goto system is within reach of us mortals. Kudos
to the original designer and for making it public.

Yes, we are all grateful to Howard Dutton for creating and sharing OnStep with the world ...

By the way, most companies that sell mounts do not develop the controllers firmware in-house at all.
For example, the Gemini system for Losmandy was developed by Rene Goerlich <http://www.docgoerlich.de/Gemini.html>.
And that is why they don't continue to improve it at the same pace that OnStep does ...


W Maxwell
 

On Tue, Sep 29, 2020 at 02:05 PM, Henk Aling wrote:
The Instein deal
The Instein setup is extremely tempting. A bit more money certainly, but looks great and is quite close to "turn key".

Again, many thanks to all for the replies. Very very informative, useful, and clarifying.


George Cushing
 

On Tue, Sep 29, 2020 at 01:42 PM, Dave Schwartz wrote:
You will also see 'unipolar' which supports designs from the stone age
Hey what's this, another diss of my Neanderthal ancestors!!? They've been gone for 30,000 years. No, in 1960, the large-angle type PM step motor was the most used step motor. This two-phase, bifilar wound PM step motor advanced 45° mechanical with each pulse from the drive, while by 1962 PM step motor drives  were using halfstep 22.5° mechanical excitation strategies to try to smooth motion.


W Maxwell
 

Guilherme:  Does the Instein for the GM8  come "preprogrammed" with these settings (below) ? Apart from the physical installation (including fine tuning the worms if needed...) and software "on the other end" (ie phd2, planetarium, wifi receiving device..) is the unit preconfigured for the combination of mount/new motors/onstep?

Looking ahead, are there configurable parameters, for example, which would balance tracking accuracy vs slew rate. In others words, if I wanted better tracking, but was willing to trade off some slew speed, is that something that can be fined tuned? Am I understanding correctly, though, that you saw an improvement, or at least no loss, of tracking quality with the parameters that came "stock" with the Instein and GM8?

In looking at the Instein webpage, it seemed there were some very useful tools: meridian flip options, and a "motion limit" to keep the scope from hitting the pier. Am I correct about these options, especially the "motion limit".  Are there others that you found especially useful? Are these generally available via any onstep/mount combination?

Again, many thanks to all who have replied. You have all been very helpful.

On Tue, Sep 29, 2020 at 02:34 PM, "Guilherme Vênere wrote:
// AXIS1 RA/AZM
// see https://onstep.groups.io/g/main/wiki/6-Configuration#AXIS1
#define AXIS1_STEPS_PER_DEGREE     12800.0 //  12800, n. Number of steps per degree:                                          <-Req'd
                                          //         n = (stepper_steps * micro_steps * overall_gear_reduction)/360.0
#define AXIS1_STEPS_PER_WORMROT   25600 //  12800, n. Number of steps per worm rotation (PEC Eq mode only:)                <-Req'd
                                          //         n = (AXIS1_STEPS_PER_DEGREE*360)/reduction_final_stage

#define AXIS1_DRIVER_MODEL            TMC2130_QUIET //    OFF, (See above.) Stepper driver model.                                      <-Often
#define AXIS1_DRIVER_MICROSTEPS       64 //    OFF, n. Microstep mode when tracking.                                        <-Often
.....etc


ybaransky
 

Hi - I bought the Instein version for the gm8. works great. the package comes with motors and controller and an optional SHC. it is all preconfigured to work as a unit, so you need to replace the existing Losmandy motors with the ones Instein provides. I did not have to enter any parameters. zero. part of its appeal.
-yurij