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Calculations needed for spur gear drive

Tom Gideon
 

Hi,
I'd like to configure a system for (ok...) a Criterion 4000. It's been refurbished and the optics are actually good. The main gear is a 217 tooth 48P gear being driven by a 13 tooth gear attached to a .75 RPH motor. I had to replace the motor with a 220VAC unit and I'd just as soon do away it.
I've been trying to figure out what stepper motor configuration would work and I'm stuck. Any help would be appreciated!
Thanks,
Tom


Re: Focuser for MaxEsp3

Ken Hunter
 

MaxESP3...

I have just measured my Vref voltage on my drivers. I have 2 ea LV8729 setup for RA/DEC
they have a Vref of 0.3000 volts (close enough) and 1 8825 driver for the Nema 11 Focuser
also set at 0.3000 volts Vref. I can exchange the drivers 8825 and 8729 with no other changes
and the behaviour is the same. I dislike the RJ type connectors so I have just used some pins
and sockets for very reliable connections.

I'll second what was said earlier about the focus motor moving VERY slow. So much in fact was
moving... after about 5 seconds the fast speed kicked in and the motion was then apparent.

I'm taking the liberty of sending a few photos of my system so you might see what does work
in practice. One photo shows where I have put an in-line focus disconnect to make disasembly
of the scope from the mount easier. 

Ken


Re: Focuser for MaxEsp3

Ken Hunter
 

I don't understand why you are passing enough current that the motors and wiring are getting hot.
I am using 2 Nema 17 steppers on Ra/Dec and an Nema 11 for Focuser on my MaxESP3 setup.
They have been continuously powered up on the bench for 3 weeks and its difficult to tell that they
have increased in temperature from ambient. In fact holding one that is disconnected in one hand
and a connected one in the other hand they are so close to the ambient temperature of the room
that I totally disregard the setup as far as the curent is concerned. I suppose that I could measure
the temperature rise for youThey work as they should and have given not one second of trouble.


Re: Can't get less than 1" total RMS

Henk Aling
 

On Wed, Jul 21, 2021 at 06:12 PM, Khalid Baheyeldin wrote:
Henk,

You can still set the guiding speed to 0.5X on 3.16.
From the Android app, press Guide/Focus.
From there, press the 3 dot menu, then select that speed.
Ahh.  I always use Guide/Focus for manual control by setting the rate to the maximum.  I must have jumped to conclusions as to what it is meant for.  The code actually maxes it to GuideRate1x so I guess that's why it all works.

Meanwhile I hard-coded it in my v4.24 Git branch, and it shows up as 0.5x so I'm good.  But thanks for noting that, next time it will be easier.

Note that whenever you (or any software) change the speed to 1X, that will stick and replace 0.5X.

I recommend that you use PHD2, because it will log guiding details for you, and you can use the phdlogview tool to see what is going on after the fact.
PHD2 is a pain to use with Ekos.  I have two imagers and one time it picked the wrong one, it took me a while to figure it out.  It does not know the Ekos device configurations.

Ekos also provides a log, it is simply an Excel spreadsheet which is just as easy for me at least.

I want to try PHD2 a bit more though but not on a regular basis unless I have to.

Finally, where do you live? Seeing is worse in some places than others (e.g. Great Lake area vs. Hawaii or New Mexico).
Just outside Santa Barbara, Bortle 5 or 6, and yes it had been a warm day. 


Re: Can't get less than 1" total RMS

Khalid Baheyeldin
 

Henk,

You can still set the guiding speed to 0.5X on 3.16.
From the Android app, press Guide/Focus.
From there, press the 3 dot menu, then select that speed.
Note that whenever you (or any software) change the speed to 1X, that will stick and replace 0.5X.

I recommend that you use PHD2, because it will log guiding details for you, and you can use the phdlogview tool to see what is going on after the fact.

Finally, where do you live? Seeing is worse in some places than others (e.g. Great Lake area vs. Hawaii or New Mexico).


Re: Focuser for MaxEsp3

Seven Jones
 

On Tue, Jul 20, 2021 at 07:16 PM, Mike Ahner wrote:
Seven, your 4-pin cable looks like a voice cable. Measure the resistance of the wire from each end, I think you will have a very high resistance. If so, that will cause a large voltage drop and the wire will start to heat up, as well as the motor. I don't see any reason at all that you should need a NEMA 17 or high current for a focuser, unless the focuser is damaged in someway that makes it very stiff to move.

Yes you are right. I have used a voice cable. thats why it getting so warm.
Unfortunately, I have already soldered the RJ10 sockets on the board. Therefore, only the 4P4C plugs fit on the board side.
Should I remove the RJ10 sockets or is there another solution?

Here are the steppers. left 60mm, right 30mn

The NEMA17 30mm was just too hot. You could not touch it. That's why I took one with 60mm. He is also pretty hot but not so much. And it was the only one I had.




Re: Can't get less than 1" total RMS

Henk Aling
 

On Wed, Jul 21, 2021 at 12:52 PM, "Guilherme Vênere wrote:
Phd2 offers multi star guiding which can visibly improve the guiding accuracy. I use it since it was implemented and following some suggestions from friends also using it, I decreased the exposure times to 1s only and I could see a big improvement in my GM8 with OnStep. The reason for it to work in PHd2 is the multi star guiding which can compensate for seeing errors.
Ekos also has multi-star guiding, this is what I use.

Right now with my G811G and Gemini I can get around 0.6" to 1" RMS without much tweaking which is more than enough for me. 
It depends on the FOV, with an ASI2600MC (an APS-C sized sensor) and 1380 mm FL.

Guide rates may depend on the type of issue your mount shows. In general 0.5x is the recommended rate. You can change that from OnStep web interface but the default at least in 4.xx should be that already.
Ah OK.  I am still using the old stable v3.16o but I now see on the Wiki that the stable version is v4.24.  That is great, let me switch to it.  I hope the guide rate is now configurable through Config.h.

.28" step already tells you you won't be able to achieve .25" accuracy. Maybe you need to change your gear ratios or microstep to get a better step ratio. I have the same motors in my GM8 and i use 64 microsteps with it without any problem.  
Will do.  Thanks!


Re: Can't get less than 1" total RMS

"Guilherme Vênere
 

Just a few takes at it but im not an expert.

Phd2 offers multi star guiding which can visibly improve the guiding accuracy. I use it since it was implemented and following some suggestions from friends also using it, I decreased the exposure times to 1s only and I could see a big improvement in my GM8 with OnStep. The reason for it to work in PHd2 is the multi star guiding which can compensate for seeing errors. Right now with my G811G and Gemini I can get around 0.6" to 1" RMS without much tweaking which is more than enough for me. 

Guide rates may depend on the type of issue your mount shows. In general 0.5x is the recommended rate. You can change that from OnStep web interface but the default at least in 4.xx should be that already.

.28" step already tells you you won't be able to achieve .25" accuracy. Maybe you need to change your gear ratios or microstep to get a better step ratio. I have the same motors in my GM8 and i use 64 microsteps with it without any problem.  

just my .02c

Guilherme

On Wed, Jul 21, 2021 at 9:38 AM Henk Aling <haling@...> wrote:
My system is a G11S with OnStep v3.16o, CNCv3 with TMC2130 drivers set at 32 microsteps configured for mode switching and the TMC2130_VQUIET model and 17HM15-0904S steppers (0.9 degrees).  I added DIY spring loaded worms and run it with a 12" Newt with FL=1380 mm, an OAG with an ASI120MM mini guider, altogether 50+ lbs of gear.  OnStep is controlled by Ekos with its native autoguider.  Slewing / goto works great especially with the SLW that prevent the ring gear from binding up, which unfortunately, happens a lot with Losmandy when trying to minimize the backlash.

While I read that several G11 owners achieve 0.25" total RMS, I can't get below 1" - well just once I achieved 0.49" in a session where I had mostly 0.6" over all but that was just once.  I understand that the seeing matters but so do a number of configuration parameters such as exposure time.  This makes me wonder if there is something wrong with my configuration.  I have played around enough with the SLW (also simply disabled them) and guider (tried PHD2 also) that I believe I can eliminate them as the cause.  My PA is good (I use Ekos with plate solving, similar to SharpCap), and my PE is probably around +/- 5" though this depends on the mechanical conditions such as how the worm blocks were set, how much counterbalance was provided and how tight the clutches were turned.  I have not yet started using Ekos' predictive PEC.  I counterbalance with a small extra weight or I put a hoodie over the counterweight.  Doing that cut my RA RMS in less than half (this was before the 1" RMS mentioned).  Guiding at 1" RMS makes images look pretty bad.  I believe that 0.25" RMS should be the norm.

1)  Is 32 microsteps accurate enough?  It leads to 0.28" per microstep.
2)  What is the best autoguider exposure time?  Losmandy users recommend several seconds and say that it matters.  I usually do 1 s, tried 3 s last night but it did not make a big difference (but I will try again).  A larger exposure time reduces the effect of poor seeing but can add errors due to guiding (the guider subs show clearly visible streaks in RA when RA is restless so it's a moving target and can cause unpredictable feedback).
3)  What is the best guide rate?  Cloudy Night users recommend not using 1x, which is the default AFAICT, this is how it shows up in Ekos.  It means that the motor comes to a full step or twice the speed.  Is that ideal, and if not, how can I change it?  I see no GUI in the Android client but there is code in Initialize.cpp that sets it to GuideRate1x that I could change.
4)  Any idea if the ASI120MM is too cheap a guider?  It provides noisy images, shaky too but that may be for the right reason.
5)  Should I switch to PHD2 instead of Ekos autoguiding?  I switched once and did not see improvement.

Only questions (1) and (3) pertain to OnStep, the other ones are uncertain factors that also affect the guiding performance.  Thanks in advance for your response.


Can't get less than 1" total RMS

Henk Aling
 

My system is a G11S with OnStep v3.16o, CNCv3 with TMC2130 drivers set at 32 microsteps configured for mode switching and the TMC2130_VQUIET model and 17HM15-0904S steppers (0.9 degrees).  I added DIY spring loaded worms and run it with a 12" Newt with FL=1380 mm, an OAG with an ASI120MM mini guider, altogether 50+ lbs of gear.  OnStep is controlled by Ekos with its native autoguider.  Slewing / goto works great especially with the SLW that prevent the ring gear from binding up, which unfortunately, happens a lot with Losmandy when trying to minimize the backlash.

While I read that several G11 owners achieve 0.25" total RMS, I can't get below 1" - well just once I achieved 0.49" in a session where I had mostly 0.6" over all but that was just once.  I understand that the seeing matters but so do a number of configuration parameters such as exposure time.  This makes me wonder if there is something wrong with my configuration.  I have played around enough with the SLW (also simply disabled them) and guider (tried PHD2 also) that I believe I can eliminate them as the cause.  My PA is good (I use Ekos with plate solving, similar to SharpCap), and my PE is probably around +/- 5" though this depends on the mechanical conditions such as how the worm blocks were set, how much counterbalance was provided and how tight the clutches were turned.  I have not yet started using Ekos' predictive PEC.  I counterbalance with a small extra weight or I put a hoodie over the counterweight.  Doing that cut my RA RMS in less than half (this was before the 1" RMS mentioned).  Guiding at 1" RMS makes images look pretty bad.  I believe that 0.25" RMS should be the norm.

1)  Is 32 microsteps accurate enough?  It leads to 0.28" per microstep.
2)  What is the best autoguider exposure time?  Losmandy users recommend several seconds and say that it matters.  I usually do 1 s, tried 3 s last night but it did not make a big difference (but I will try again).  A larger exposure time reduces the effect of poor seeing but can add errors due to guiding (the guider subs show clearly visible streaks in RA when RA is restless so it's a moving target and can cause unpredictable feedback).
3)  What is the best guide rate?  Cloudy Night users recommend not using 1x, which is the default AFAICT, this is how it shows up in Ekos.  It means that the motor comes to a full step or twice the speed.  Is that ideal, and if not, how can I change it?  I see no GUI in the Android client but there is code in Initialize.cpp that sets it to GuideRate1x that I could change.
4)  Any idea if the ASI120MM is too cheap a guider?  It provides noisy images, shaky too but that may be for the right reason.
5)  Should I switch to PHD2 instead of Ekos autoguiding?  I switched once and did not see improvement.

Only questions (1) and (3) pertain to OnStep, the other ones are uncertain factors that also affect the guiding performance.  Thanks in advance for your response.


Re: New Project. G11 and OnStep. Which Board, CPU.

Pete
 

Thanks Howard.  5V compatibility is always handy I'll order a Teensy 3.5.  Done.

Here's the board I ordered from JLCPCB.  I am sorry I did not specify the board.  I just figured everyone was now using the MaxPCB2, as I now shall.


Re: FYSETC S6 Focuser dosnt move #fysetc #S6

Juan Sebastian
 

Ok totally my fault, the motor was moving too slow, that i cant percive the movement, i adjusted the config, and now everithing works ok


Re: Connect gearbox and confing help #mount #configuration

George Cushing
 

Commercial step motors came on the scene in 1960 with 6 steps, IIRC.  Nippon Pulse Motor was established in 1962. The PF42-48 made its appearance as part of the Vixen DD and MD drives for the Super Polaris and Polaris in the mid-'80s. They continue to be made and sold to this day. 

In Europe the DK-3 dual drive for EQ-5 mounts and the DK-V for EQ-2 and 3 mounts are sold. They use the current version of the PF42, the PFC42H 48081 with the 1/120 gearhead. Current draw is 0.28A when operated at 5V. Ordinary torque output is 400mN-m. "Destructive torque" is said to be 1200mN-m.

I guess that durability is the reason I get a few requests a year for information on replacing a DD or MD controller. In terms of effort and expense I always offer the OnStep solution. Folks insist they don't want goto. Tell them then ignore it. Otherwise the time spent building something from scratch and coding for each application is prohibitive.

Synta has been selling E2, 3, 4 and 5 drives since the early '90s through Orion and Celestron. They use 42PM series step motors from the Chinese maker MotionKing. These are 24 step designs and thus use high gear reductions to smooth out the pulses. The early Orion Sirius (HEQ5) and Atlas (HEQ6) used similar MotionKing drives. The Atlas had a 1/397 reduction ratio gearhead. Now try to get some slew speed from that!


Re: OnStep fails completely!!!

Howard Dutton
 

On Wed, Jul 21, 2021 at 03:43 AM, András wrote:
can you tell me which hardware you used to handle the encoder and the external drivers (I suppose)?

I tried it on a MaxESP but it is sensible to the levels and will not start with the external driver connected.
If you could elaborate, such as details about the hardware attached to the MaxESP3, I might be able to comment.


Re: OnStep fails completely!!!

András
 

Hello Thomas,

can you tell me which hardware you used to handle the encoder and the external drivers (I suppose)?

I tried it on a MaxESP but it is sensible to the levels and will not start with the external driver connected.
A CNC3 is better but the Wemos ESP8266 has problems handling the encoders, the wifi fails to init normally.


Re: New Project. G11 and OnStep. Which Board, CPU.

Howard Dutton
 

On Wed, Jul 21, 2021 at 03:20 AM, Howard Dutton wrote:
On Tue, Jul 20, 2021 at 07:25 PM, Pete wrote:
Question: Should I go with a Teensy 3.5 or 3.6?  The 3.6 is faster 180 Mhz vs 120 for the 3.5 and the 3.6 has double the memory.  However the 3.5 has all pins tolerant of 5V, which may be useful.
The 5V tolerant pins are handy.  I don't anticipate you needing the speed of the T3.6
Just be sure the board you ordered is a MaxPCB2!  You really didn't say.


Re: New Project. G11 and OnStep. Which Board, CPU.

Howard Dutton
 

On Tue, Jul 20, 2021 at 07:25 PM, Pete wrote:
Question: Should I go with a Teensy 3.5 or 3.6?  The 3.6 is faster 180 Mhz vs 120 for the 3.5 and the 3.6 has double the memory.  However the 3.5 has all pins tolerant of 5V, which may be useful.
The 5V tolerant pins are handy.  I don't anticipate you needing the speed of the T3.6

My Teeny 3.2 in my old mniUSB boards work just fine.  I plan on using TMC5160s as a final solution. 

Does this affect the CPU choice?
No.


Newbie plan to install onstep

Pengembara T.
 

Hi Everyone,

This is my first post here so first of all, thank you to Howard for
creating this project and thanks to all senior members who are helping
other members.

I have a dream to install onstep on my homemade dobsonian mount, need
some suggestion:

1) Motor: I want to get a high builtin gear ratio motor, found
17HS19-1684S-PG100 from OMC stepperonline. Looks like it is not 400
steps/rotation and not 0.9Ampere. It is 200 steps and 1.68A.

What is the difference in terms of power requirement between 0.9A vs
1.68A ? Plan to use a laptop charger. No plan for remote viewing using
a battery.

2) Stepper Driver : LV8729. Is it ok to use LV8729 ? Its maximum drive
current is 1.8A.

And from what I read from this group, we only use around 40% - 70%
from max, so for a 1.68A motor, it should be below 1.2A. Is it correct
?

If LV8729 cannot be used, what is the recommended stepper driver ?

3) Gear wheel. To get a high reduction ratio, I plan to make some big
gear wheels.

There is an article at instructable to use the GT2 timing belt as
gear-wheel, but in that scenario, the gear wheel is used by the
encoder. Not to drive the telescope.
Source: step 2 from
https://www.instructables.com/Control-Your-Telescope-Using-Stellarium-Arduino/

Question: Can I use a GT2 pulley as a gear wheel ?

4) Microcontroller.
Slow Slewing speed is not a concern for me as a beginner.

If LV8729 can be used as a stepper driver, then my choice for
microcontroller is wemos + CNC3.


If the recommended stepper driver is not LV8729, then can I use MKS Gen-L ?


Question about Onstep operation / astronomy in general:

My plan is to track the moon, Jupiter and saturn.

Currently we use a telescope through the balcony. Our view is limited
to a maximum of half sky.
And the light pollution is a little high. Not many stars are visible at night.

Reading from onstep documentation that we need to align to 3 stars to
be able to track objects.
question:
1) Can I use Jupiter / Saturn as an alignment star ?

2) Can I use static objects like towers, or rooftop building lamps as
additional helpers ? as we can find the GPS coordinate of that tower
and also for the building.

3) Lets say my alignment is wrong because I cannot find enough stars.
What happens if we are forced to continue tracking Jupiter ? I guess
it will be inaccurate / out of field view.

Can I fine tune (to make Jupiter inside the field of view) for 1 or 2
first minutes and after that onstep learn and be able to continue
tracking correctly ?

sorry for my english.

Thank You.


Re: New Project. G11 and OnStep. Which Board, CPU.

Pete
 

The case and the PCBs are on order.  I have stepper motors and drivers kicking around even though they are only 8825s, they will get me going.

Question: Should I go with a Teensy 3.5 or 3.6?  The 3.6 is faster 180 Mhz vs 120 for the 3.5 and the 3.6 has double the memory.  However the 3.5 has all pins tolerant of 5V, which may be useful.  My Teeny 3.2 in my old mniUSB boards work just fine.  I plan on using TMC5160s as a final solution.  Does this affect the CPU choice?

Thanks.


Re: Focuser for MaxEsp3

Mike Ahner
 

On Tue, Jul 20, 2021 at 01:28 PM, Seven Jones wrote:
so far it works well. Besides that 4 pin 4p4c cables is pretty hot. Href is 0,75V.
Seven, your 4-pin cable looks like a voice cable. Measure the resistance of the wire from each end, I think you will have a very high resistance. If so, that will cause a large voltage drop and the wire will start to heat up, as well as the motor. I don't see any reason at all that you should need a NEMA 17 or high current for a focuser, unless the focuser is damaged in someway that makes it very stiff to move.

Try a Cat-5 cable, you can temporarily strip back just 4 wires and twist them onto the motor wires. I think you'll find there is a big difference.


Re: Custom Ethernet and INDI: no persistent channel?

Jordi Sese
 

Hi Howard,

Great! this time I only had to modify config.h to select W5500 ethernet mode and it connected/worked fine!!!
It's cloudy right now so I cannot test it for a full session, but it looks good to me using it home with the ccd simulator.

Thanks a lot for your help. 

Regards from Barcelona,

Jordi.

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