Re: Occasional error in guide speed - massive overcorrections


While you're here, Howard, I was wondering if you might have any idea about a couple of things.

I know you don't use APT, but it seems I cannot use a slew rate slower than 2x sidereal, or 0.00835654 degrees/sec.  Anything lower than this results in an error.  I notice that the ASCOM device hub, under capabilities, it shows primary and secondary axis rates as .00833 - 2.00000.  Perhaps this is connected to the reason APT cant move slower than 2x?  Any way to adjust this?  I don't see anything obvious in the driver.  I assume this is a slew rate limitation and not a pulse guide rate limit, since I can manually pulse guide in PHD2 at 0.5x just fine.  However, confusingly, this seems to be what changes the pulse guide rate resulting in my wild overshoots while guiding.  I'm scratching my head trying to make sense of it.

Also, a quick side question that doesn't warrant it's own thread.  Is there any way to issue a Find/Home command or a Home/Reset command from ASCOM (device hub, poth, or any clients using the ASCOM driver)? 

Thanks for any insights,

On 5/27/2021 10:37 AM, Howard Dutton wrote:
Thanks for the heads up, I'll keep this interaction in mind.

Re: MiniPCB v2 - Teensy 3.1 losing communication with wemos #wemos #wifi

Howard Dutton

Glad you seem to have it sorted.

Re: Occasional error in guide speed - massive overcorrections

Howard Dutton

Thanks for the heads up, I'll keep this interaction in mind.

Re: My DIY Friction Drive Mount #maxesp3 #cnc #diy #mount #esp32


Backlash was the reason I ask about the mechanism for applying normal force for the friction drives.  Looks like you did a great job! I would evaluate performance for a while before you consider adding encoders, as I expect slippage will not be an issue - but you know the mounts capability better than I.

Re: hello everyone, i have a new question. If I install a powerful servo motor with encoder instead of stepper motor, will the system work? #mount

Howard Dutton

The Step/Dir interface is an industry standard and is not limited to driving stepper motors.

There is no end to the options available, most of us use stepper motors with open loop control since it's cheap and effective.  I doubt the scale of whatever "larger telescope" is beyond something that can be handled by a stepper motor of some sort but nothing stopping you from using a servo.

Here's another source that's been mentioned here before:

Re: My DIY Friction Drive Mount #maxesp3 #cnc #diy #mount #esp32


Thank you John for yor reply and suggestions. Yes, an encoder may be worth it , and I'll take it in consideration in the next "release" if there will be one....but It will be an High resolution one for sure. 

@Gildo I'm from Brescia 🙂

Zhumell Z8 Dobsonian accuracy troubleshooting/showcase #dob #backlash #maxesp3


Alright, so I've had a night out under the stars with my telescope! I had to increase stepper current to 1000 and decrease microsteps to 32 as I was running into stalling problems due to high RPMs on the stepper motors. I don't know if that was overkill, but I am pretty sure that solved the issue. 

Here's my build so far:
I used Nema 17 motors with 100:1 gearboxes, then going from a 40 tooth gear to a 320 tooth gear for an 8:1 ratio. I had to make belt tensioners in order to get things tight enough. I just bought a 5 meter length of GT2 belt from amazon, and used a 3D printed belt clamp on the altitude axis, and I sanded 2 inch sections and Gorilla Glued the belt together for the azimuth axis. So far after a week of being under tension, all seems good! 

So far, I've been having issues with figuring out backlash, which using the method layed out on the wiki, I am using 960 for the altitude, and 300 for the azimuth. Do these sound like they could be in the right range? After doing a 3 star alignment, here is the view that I get with my aligned laser when slewing to a star for reference. It is probably more than a moon's width away from the target star. Is this a good level of accuracy? 

Besides that, I just really don't understand how the backlash feature works.. Because even when I align it with the star, because of the backlash it doesn't track the star until it has moved around significantly in the eyepiece, usually leaving the view. 

I'll also link my config file and Excel spreadsheet.

Re: G11 Dual Axis & G8 Single Axis Configration #configuration


On Wed, May 12, 2021 at 04:07 AM, Dave Schwartz wrote:

Final slove the issue..

CP2102 not able to detect or not able to upload error was fix... it was duel to board manufacture issue, connection RXT n TXD after solder both wire it able to connect just fine... ( i think the board trace line to thin or manufacture defect )


Re: hello everyone, i have a new question. If I install a powerful servo motor with encoder instead of stepper motor, will the system work? #mount


I find it worth a shot.
Because my goal is a bigger carrier. and connect and operate a larger telescope

Re: MiniPCB v2 - Teensy 3.1 losing communication with wemos #wemos #wifi


Hello Howard,

Thank you for replying.

I am, indeed, using release 4.24.

I tested the board using an HC05 without problem, and tested it through WiFi as well using the same cellphone (Samsung Galaxy S21) and SkySafari. It all seemed to be working fine.
...except OnStep app kept crashing.

I noticed the app kept getting worse, though. So I cleared the app cache and data, and I have not been able to make this thing crash anymore.
Not yet, at least :D

Now to do some testing using an actual telescope...



Howard Dutton

On Tue, May 25, 2021 at 05:11 PM, Howard Dutton wrote:
  • The scroll rates when entering numbers are pretty fast.  The rates also change rather quickly.  It's easy to overshoot your mark and difficult to get within a minute of desired time.  Setting of coordinates (in goto) has the same issue.
A known issue, I'm busy with other stuff.
I added code to regulate the scroll speed when navigating the u8g2 interface, this includes the menus and also controls for setting values.

Rather than using a fixed scroll speed I implemented acceleration, so at first it moves slowly then after about 5 seconds it's very fast.  This is needed since some of the catalogs are quite large and would take forever to scroll through otherwise.

Seems to be working quite nicely here.

Re: hello everyone, i have a new question. If I install a powerful servo motor with encoder instead of stepper motor, will the system work? #mount

Khalid Baheyeldin

On Wed, May 26, 2021 at 04:13 PM, sami wrote:
If I install a powerful servo motor with encoder instead of stepper motor, will the system work?
In general, OnStep is desgined for stepper motors, in an open loop design (i.e. no feed back from an encoder).

However, there are some specialized stepper drivers that are able to drive servo motors.
They are driven by Pulse and Dir pins, and therefore can be driven from OnStep controllers, with some rewiring.
Pulse is the same as Step in stepper motors.


Re: My DIY Friction Drive Mount #maxesp3 #cnc #diy #mount #esp32

John Petterson


This is phenomenal work.  Thanks for sharing what is possible. 

With a friction drive, you might want to consider adding a set of encoders to the mount that would allow you to maintain the OnStep's alignment if the mount gets bumped, or if you manually swing it to another target.  I know there are steps you can take through the menus to sync it to the new location as well.  But the machine work on this is very nice.

Re: My DIY Friction Drive Mount #maxesp3 #cnc #diy #mount #esp32

Gildo Bosi

Fantastic project, congratulations, what city are you from?

Gildo (Bagnacavallo, Ravenna)

hello everyone, i have a new question. If I install a powerful servo motor with encoder instead of stepper motor, will the system work? #mount


hello everyone, i have a new question.  If I install a powerful servo motor with encoder instead of stepper motor, will the system work?

Re: Home sensors

Howard Dutton

On Tue, May 25, 2021 at 07:43 AM, Martin Bonfiore wrote:
Personally, I would prefer to establish a mechanical reference when powering the telescope mount back up using the HOME sensors.  In my implementation, they are opto-interrupters with a few microns of repeatibility error.  On the other hand (based on my understanding which could be mistaken) the designers of Onstep chose to base the PARK/UNPARK operaton on an assumption that the mount and the relationship of the telescope to the mount did not change between power on and power off sessions. 

The case that the scope did not move is for most cases very reasonable in my opinion...any movement would require (for most implementations) back driving a worm gear which is typically not possible and/or bumping the scope such that any clutches slipped.  

While I accept that argument and certainly highly respect the designers (I could not have designed this system), I have been experimenting with changing the software (small modifications) in order to change the HOME with sensors operation to allow the homing after power up approach without needing to redo the alignment.  I am not sure where this will take me...understanding the code has not been easy for me, but certainly an interesting challenge and I have gained a great appreciation of what it takes to provide Onstep functionality.  I am no where close to sharing anything in that regard since my hacking is at the moment, not well understood or tested.
Think this should work in release-4.24 ...

Just find this line in OnStep.ino:
VLF("MSG: OnStep is ready"); VL("");

Then add this one under it:

Having the mount do an un-commanded rapid motion on startup is not a feature I will be adding.

I understand the appeal of (the option for) doing a home operation before the first Goto and that doesn't seem especially worrisome to me, just takes more effort to stage the events so not trivial and so not something I'll add to 4.24.

Re: Home sensors


Thank you for replays. I will make this solution in Ekos starting script. I will add:
If mount is not parked goto home, home restet, etc. If mount is parked after power on run normal startup procedure.

I have to learn dbus interface to KStars. In onstep  wiki I found that if home sensor are used i dont have to align?. I always do plate solving so I don't need good model and super point acurracy before plate solve in Ekos. 

Re: My DIY Friction Drive Mount #maxesp3 #cnc #diy #mount #esp32

Howard Dutton

Not too much difference between RA (0.53") and Dec (0.47").  Most noise happened in bursts, perhaps wind.
Looks promising to be capable of better.

Re: My DIY Friction Drive Mount #maxesp3 #cnc #diy #mount #esp32


Oh, I'm sorry Khalid.

In the first image  was

0.71" RMS, the 2nd one 0.66" RMS 🙂

Re: My DIY Friction Drive Mount #maxesp3 #cnc #diy #mount #esp32

Khalid Baheyeldin

I can't read the RMS numbers in the guiding graph screenshots.
Can you please send them as a reply, in text form? Everyone can read text.

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