Date   

Re: Microstepping or gearbox... #EQ5 #esp32 #bluepill

Henk Aling
 

On Sat, Jul 24, 2021 at 08:39 AM, <nicholas.welham@...> wrote:
I have built and largely tested a Bluepill but still need to finalise the steppers for an EQ5. I have a couple of 1.8deg nema8 motors with pg90 gearboxes which have more than enough torque to do the job. However, there seems to be very little information on the relative merits of microstepping vs. gearboxes for reduction. Microstepping reduces torque leading potential jerkiness, gearboxes eliminates microstepping but increases backlash. There is no problem getting high steps per degree, 200 steps x 90.25 gearbox x 3 pulley x 144 worm / 360 deg = 21660 steps per deg without microstepping.
The vast majority of builds seem to prefer microstepping, is this mainly to do with cost of gearboxes, hovever since the best microstepping drivers are a significant cost too eliminating microsteps reduces the need for smoothness of chopping.
Am I missing something important?
Thanks.
If you go with micro stepping you may be better off going with 0.9 degree steppers.  I am worried about the loss of incremental torque of my 36 Ncm steppers, and compared it with 65 Ncm 1.8 degree steppers.  The incremental torques look like this:



Here, the log2 has been shifted up by 1 for the 1.8 degree stepper so the X axis represents the same angles on the 0.9 degree stepper scale.  This is based on Tinc=sin((pi/2)/nMicroSteps).

Gearboxes lead to additional backlash and PE.  This backlash is more of a problem for DEC less so for RA while the PE is more of a problem for RA.  Personally I don't like having backlash in a mount for slewing.


RA Drift

Jamie Flinn
 

Hi All…

 

I was diagnosing guiding issue last night and solved a mechanical issue that put my guiding back into the realm of “normal”, but as part of that diagnosis I was using the PHD2 Guiding assistance and I was seeing as listed drift in RA that was westwards (read as too fast?) – this tool looks at the guide star without guiding motions, so the “lock position” vs real position is measured.  The drift was noticeable and something like 3” per minute.

 

So I move on and start guiding (got a whole night surprise surprise) and I can see that using INDI/EKOS I was again getting consistent guide-east pulses – put the two together and the obvious answer is the mount is running westward faster than sidereal

 

Pointing is great and I plate solve in very few iterations…but that westward motion I need to kill

 

Can I use the “Frequency –“  function for this (or is it perhaps Frequency + ?) – or would you suggest I play with the worm numbers in config?

 

This is every so slight but it does cause ping pong guiding in RA when DEC is hitting RMS values of 0.34

 

Thought? Opinions?

 

Cheers

Jamie

 

 

 

Sent from Mail for Windows 10

 


Re: Stepper motor driver TMC2130 vs LV8729 #diy #dob

Henk Aling
 

On Sat, Jul 24, 2021 at 11:32 AM, Khalid Baheyeldin wrote:
The TMC2130 is very quiet, even quieter than the LV8729 which is fairly quiet compared to the conventional drivers. When tracking either is almost silent. When slewing the LV8729 emits a bit more noise than the TMC2130, but not much.
It's  very quiet in TMC2130_VQUIET mode, the other modes can be pretty noisy.

A few things you did not consider:
- Not all boards support switching microsteps for all drivers. For example, the FYSETC S6 and MKS Gen-L v2 can switch only with the TMC2130 and TMC5160. So board choice needs to be factored in before driver choice. Not sure if the CNC supports SPI or not. Its Wiki page should say, but as I recall from past discussions, it requires more soldering and such.
If you wire the CNCv3 up properly it supports mode switching, no soldering needed just some wires with female pins.  I should mention that I created my own pin map and wiring scheme because the CNCv3 was not supported in v3.16.o .  It enhanced my understanding so not a bad thing.  The CNCv3 does not support SPI mode switching in the same way as the MKS board does so maybe that means it doesn't but you can wire it up yourself like I said.


Re: Stepper motor driver TMC2130 vs LV8729 #diy #dob

Khalid Baheyeldin
 

Great that someone is reading extensively before building and before asking questions ...

Yes, you generally do not want to rely on extreme microstepping in lieu of gear reduction. Torque is one factor, accuracy of microsteps is another. Using 1/16 or 1/32 is the general rule.

Yes, PULSE works on both.

Using a different microstepping for slewing works on both. Ignore the technical details. The TMC2130 no longer loses microsteps when switching, at least in OnStep 4.x (current stable).

The TMC2130 is very quiet, even quieter than the LV8729 which is fairly quiet compared to the conventional drivers. When tracking either is almost silent. When slewing the LV8729 emits a bit more noise than the TMC2130, but not much.

A few things you did not consider:
- Not all boards support switching microsteps for all drivers. For example, the FYSETC S6 and MKS Gen-L v2 can switch only with the TMC2130 and TMC5160. So board choice needs to be factored in before driver choice. Not sure if the CNC supports SPI or not. Its Wiki page should say, but as I recall from past discussions, it requires more soldering and such.

- Both can drive low current motors, but may not drive motors with more current. So motor selection factors in too. For example 400 step 0.9A motors can be driven by either. The 1.68A motor can too, provided that you stay at the recommended 40% (1.68 x 1.41 x 0.4 = 0.948A)

- The TMC2130 can heat up considerably and some people need to add fans to their case. The LV8729 never has this problem.


Re: Config.h modification

Dahle
 

‌Un GRAND Merci !
Aussi je continue de parler Français pour éviter toute mauvaise traduction.
Je vais commencer par le début:
J'ai reçu une monture Trident de Mark de JTW Astronomy  (Hollande) (voir photo) avec contrôleur Onstep.
Malheureusement, après test, le moteur RA tourne dans le mauvais sens!
Je fais les tests sous Windows 10.
j'envoie toutes les photos nécessaires pour plus de compréhension.
Ma question principale est: peut-on modifier le config.h pour inverser le sens du moteur sans avoir le source du config.h et sans modifier les autres paramètres. 
j'ai installé  Onstep/ Arduino 1.8.15
La carte est une bluSTM32 Blue Pill.
Module WiFi: ESP 8266
Motor driver: TMC 2130
Une fois ce problème résolu, je me préoccuperai du WiFi.
Pour le WiFi, Mark me dit de reflasher... plus facile à dire qu'à faire !
Alain

a big thank-you !
Also I continue to speak French to avoid any bad translation.
I'll start from the beginning:
I received a Mark Trident mount from JTW Astronomy (Holland) (see photo) with Onstep controller.
Unfortunately, after testing, the RA motor turns in the wrong direction!
I am doing the tests on Windows 10.
I send all the necessary photos for further understanding.
My main question is: can we modify the config.h to reverse the direction of the motor without having the source of the config.h and without modifying the other parameters.
I installed Onstep / Arduino 1.8.15
The card is a bluSTM32 Blue Pill.
WiFi module: ESP 8266
Motor driver: TMC 2130
Once this issue is resolved, I will be concerned about the WiFi.
For WiFi, Mark tells me to reflash ... easier said than done!
Alain

 
 
De : "alain"
A : main@onstep.groups.io
Envoyé: samedi 24 Juillet 2021 15:10
Objet : Re: [onstep] Config.h modification
 

I apologize for writing in French but I want to help this guy.

Bonjour,

si tu veux je peux t’orienter un peu pour ce qui est de la configuration puis de la programmation d"OnStep.

Il me faut d'abord connaître un peu plus ton matériel et ton environement.

Travailles-tu sous Windows ou Linux?

Quelle marque et modèle de monture?

Tu dis que tu ne peux te connecter au WiFi? pourquoi? Mauvais mot de passe ou tu ne trouves pas OnStep dans to WiFi?

Pour ton moteur qui tourne à l'envers un recâblage du connecteur pourrait aussi faire l’affaire mais la encore il faut en savoir un peu plus pour pouvoir t'aider.

A + Alain Zwingelsein

 

Le 24/07/2021 à 11:53, Dahle a écrit :
‌Hello everyone,
I am new to the group, I am French and like any good French I do not have a good command of the English language so I trust Google Translate. I just bought a mount with an Onstep controller. I noticed that the RA motor is not turning in the right direction. I know the modification is done in config.h. Hence my questions: How to modify this parameter (AXIS1_DRIVER_REVERSE) if I understood correctly in config.h while I do not have the source (sketch?), And without modifying the other parameters? I'm trying to see how this programming works because I don't know anything about it.
For information, I do not have access to WiFi Onstep (ERR_CONNECTION_REFUSED)

Thank you
Alain
-- 
ЦВИНГЕЛЬШТЕЙН АЛЕН


Re: Microstepping or gearbox... #EQ5 #esp32 #bluepill

Oscar Lithgow
 

It depends on what you're planning to do with the telescope. If its for visual use only, you can use gearboxes. If you want to do astrophotography, its better to use bigger motor and microstepping, and a bit of reduction with belts and pulleys.
Gearboxes always have periodic errors (PE) that will become apparent when tracking, specially in RA movement in eq mounts. Higher quality gearboxes has less PE. Also the RA worm gear of the mount has PE, but this can be managed with onstep. But if you use gearboxes it will introduce more PE in addition of the PE from the wormgear.

Cheers


Re: Config.h modification

alain
 

I apologize for writing in French but I want to help this guy.

Bonjour,

si tu veux je peux t’orienter un peu pour ce qui est de la configuration puis de la programmation d"OnStep.

Il me faut d'abord connaître un peu plus ton matériel et ton environement.

Travailles-tu sous Windows ou Linux?

Quelle marque et modèle de monture?

Tu dis que tu ne peux te connecter au WiFi? pourquoi? Mauvais mot de passe ou tu ne trouves pas OnStep dans to WiFi?

Pour ton moteur qui tourne à l'envers un recâblage du connecteur pourrait aussi faire l’affaire mais la encore il faut en savoir un peu plus pour pouvoir t'aider.

A + Alain Zwingelsein


Le 24/07/2021 à 11:53, Dahle a écrit :
‌Hello everyone,
I am new to the group, I am French and like any good French I do not have a good command of the English language so I trust Google Translate. I just bought a mount with an Onstep controller. I noticed that the RA motor is not turning in the right direction. I know the modification is done in config.h. Hence my questions: How to modify this parameter (AXIS1_DRIVER_REVERSE) if I understood correctly in config.h while I do not have the source (sketch?), And without modifying the other parameters? I'm trying to see how this programming works because I don't know anything about it.
For information, I do not have access to WiFi Onstep (ERR_CONNECTION_REFUSED)

Thank you
Alain
-- 
ЦВИНГЕЛЬШТЕЙН АЛЕН


Microstepping or gearbox... #EQ5 #esp32 #bluepill

Nick Welham
 

I have built and largely tested a Bluepill but still need to finalise the steppers for an EQ5. I have a couple of 1.8deg nema8 motors with pg90 gearboxes which have more than enough torque to do the job. However, there seems to be very little information on the relative merits of microstepping vs. gearboxes for reduction. Microstepping reduces torque leading potential jerkiness, gearboxes eliminates microstepping but increases backlash. There is no problem getting high steps per degree, 200 steps x 90.25 gearbox x 3 pulley x 144 worm / 360 deg = 21660 steps per deg without microstepping.
The vast majority of builds seem to prefer microstepping, is this mainly to do with cost of gearboxes, hovever since the best microstepping drivers are a significant cost too eliminating microsteps reduces the need for smoothness of chopping.
Am I missing something important?
Thanks.


Stepper motor driver TMC2130 vs LV8729 #diy #dob

Marcus
 

Hi I'm speccing a onstep system for a 8" skywatcher F5 with a DIY dobsonian mount. Primarily for visual use at first.

I have some questions about TMC2130 vs LV8729 drivers and the advantages of either, from reading of the wiki.  This would help my choice of microcontroller either FYSETC S6 or WeMos R32 with CNC V3 Shield. I'll lay out my understanding from the wiki below.

I've read that due to lower torque at high microsteps you practically can't go below 32 microsteps (https://onstep.groups.io/g/main/wiki/16264).  So this would imply that the higher microstep of 256 for the TMC2130 is not an advantage over the LV8729 at 128 steps?

The  LV8729 (https://onstep.groups.io/g/main/wiki/4464) has On-The-Fly Mode Switching whereas the TMC2130 has Before/After Mode Switching from the wiki "In this mode of operation micro-steps can be lost so if it must be used to switch micro-step modes it is best to switch between nearby micro-step modes.  For example 32X to 16X so at worst only 1 unaccounted for (32X level) micro-step may be lost or gained."   Surely this is a bad thing for the TMC2130 as it will gradually lose position, especially for big changes in microsteps - which could help give accurate large (say 32) microsteps for tracking and smaller microsteps (say 1?) for fast goto?

The only advantage I can see for the
TMC2130 is that has very quiet movement - this may be impostant at a dark sky campsite!  The LV8729 is supposed to be quite quiet, so how much of an advantage is this?

Does #define STEP_WAVE_FORM PULSE work for both drivers?

The costs for the UK are ~7GBP for 2
LV8729s and ~12GBP for 2 TMC2130s, so cost is not a strong driver.

Thanks for your comments/help!!!!


Config.h modification

Dahle
 

‌Hello everyone,
I am new to the group, I am French and like any good French I do not have a good command of the English language so I trust Google Translate. I just bought a mount with an Onstep controller. I noticed that the RA motor is not turning in the right direction. I know the modification is done in config.h. Hence my questions: How to modify this parameter (AXIS1_DRIVER_REVERSE) if I understood correctly in config.h while I do not have the source (sketch?), And without modifying the other parameters? I'm trying to see how this programming works because I don't know anything about it.
For information, I do not have access to WiFi Onstep (ERR_CONNECTION_REFUSED)

Thank you
Alain


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

Henk Aling
 

As an aside, I tried setting the microstepping first to 256x and 128x.  For some reason the goto becomes excruciatingly slow.  I went back to 64x and goto worked normal again.  I suppose the TMC2130 or Wemos does not like those values.  They work for others.


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

Henk Aling
 

On Thu, Jul 22, 2021 at 07:10 PM, Alexander Varakin wrote:
Henk,
Can you share your guide graph for this session?
Are you getting most of error on RA or on DEC?
Can you share your unprocessed stack? I can measure the PSF for you.
I have the guide log, debug log and Autosave.tif are at

https://1drv.ms/t/s!At7g23ZLfniEogZzcmiOJVv7REFN
https://1drv.ms/t/s!At7g23ZLfniEogdzcmiOJVv7REFN
https://1drv.ms/u/s!At7g23ZLfniEogVzcmiOJVv7REFN

I tried to attach the logs but they show a cross so I think they failed.
The image of 14x60 subs is at Losmandy_users@groups.io | Photo and is at low res included below. 



There is a gradient, the neighbors still have the Christmas lights on outside.  
When you study the log, several things went wrong in the beginning.  DEC started to drift.  I loosened the clutches, still drift.  Later I found that a screw that had to be loose for the SLW was stuck.  After loosening it the SLW could work again and the rest was smooth.  Lots of bumps while I was doing that.  Eventually the clouds moved in.


Re: Newbie question #EQ5 #fysetc

Dave Schwartz
 

Yes, the BME280_SPI will work in place of the BMP280_SPI... Just change the P to E in the parameter name and you'll be going to go.


On July 23, 2021 7:00:03 p.m. EDT, marclloveras@... wrote:
Thanks a lot, Dave, Khalid and Drew.
After reading the threads posted by Khalid I realised that my wiring was not ok, 
After adding the line suggested by Dave in the config file, it worked fine.
I assume that the same wiring will work for the BME, just changing the “define WEATHER” line. I will buy one and substitute the BMP.

This the final configuration with BMP280:
 

config.h _______________________________________________________________

#define LED_STATUS2                OFF

#define WEATHER                       BMP280_SPI

#define BMP280_CS_PIN           PC7  

Wiring _______________________________________________________________

* SCL to SD-SCK 

* SDO to SP1-MISO 

* SDA to SD-MOSI 

* CSB to PC7 


--
Sent from my Android device with K-9 Mail. Please excuse my brevity.


Re: Newbie question #EQ5 #fysetc

marclloveras@...
 

Thanks a lot, Dave, Khalid and Drew.
After reading the threads posted by Khalid I realised that my wiring was not ok, 
After adding the line suggested by Dave in the config file, it worked fine.
I assume that the same wiring will work for the BME, just changing the “define WEATHER” line. I will buy one and substitute the BMP.

This the final configuration with BMP280:
 

config.h _______________________________________________________________

#define LED_STATUS2                OFF

#define WEATHER                       BMP280_SPI

#define BMP280_CS_PIN           PC7  

Wiring _______________________________________________________________

* SCL to SD-SCK 

* SDO to SP1-MISO 

* SDA to SD-MOSI 

* CSB to PC7 


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

Henk Aling
 

I am wondering if I configured my system poorly for the given load and stepper characteristics.

My stepper is 0.9 degrees configured with 64 microsteps.  My gear reduction is 360.  When I am autoguiding at the magical 0.25" RMS it is reasonable to assume that the guider tries to squash errors of around 0.25".  The step size for this after gear reduction is 360*0.25"=90".  The step angle is 0.9*3600/64"=50.625".  The number of steps the stepper needs to take is therefore 90/50.625=1.8 steps.
 
For a well defined pulse clearly we need more than 1.8 steps.  If I guided at 256 microsteps this would be 4x that, 7.2 steps.  Not perfect but a lot better.  So maybe I should use 256 microsteps?  
 
Will the torque then still be good enough depending on the acceleration associated with the pulse ramp-up time?  If it is not we will miss steps, which leads to more error and control action.  
 
The incremental microstepping torque is Tmicro = Thold*sin((pi/2)/nMicro) where nMicro=256 in this case.
 
I found this torque calculation reference at Oriental motors:
 
https://www.orientalmotor.com/products/pdfs/2018-2019/technical-reference/Technical_Reference_Overview.pdf?hsCtaTracking=72ff05cd-3657-4344-9f9a-2e6973a004d1%7C65a4e02f-5779-4945-953a-1e14fe96003b
 
I ran the math for my system:
 
- An OTA of 48 lbs placed at 1 ft from the RA axis
- Counterweights for simplicity placed at 1 ft
- A stepper with a holding torque of 0.36 Nm
- A guide ratio of 0.25
- 256x microstepping
- A static load of 2 lbs at 2 feet (like Howard used in the static stepper analysis)
- An equal amount of friction added (ditto)
- A rotor inertia of 54 g cm^2
- A ramp-up/down time that is 0.1 times the total pulse time
- A safe factor of 2
- I have not accounted for reducing Vref of the TMC2130 to half
 
The outcome of this is that, during the ramp-up, a total torque of Tm=0.0079841 is achieved, with a Tmicro=0.0088348.  Apparently, with this configuration, we are right at the limit of what the stepper can achieve.  With 0.5x guiding I would not be able to step safely.  With 64x microstepping I would not be close enough in terms of accuracy.
 
If you want to check the math or just keep me honest, here's the Scilab script.  The variable names are similar to what is used in the above link, the math was taken from the horizontal rotating table example with 10 weights.
 
// Conversion constants
kg2oz = 35.2739619;
m2in = 39.3700787;
lb2oz = 16;
kg2lb = 2.20462262;
ft2in = 12;
m2ft = 3.2808399;
Nm2ozin = 141.61193227806;
rad2deg = 180/%pi;
rad2as = rad2deg*3600;
 
J0 = (54/1000)/100^2;               // Rotor inertia in kg/m^2
Tl = (2/kg2lb)*(2/m2ft);            // Load torque for 2 lbs at 2 feet
Tl = 2*Tl;                          // Add an equal amount for friction
gearRatio = 360;                    // Gear ratio
guideRatio = 0.25 ;                  // Guide rate
dTheta = 0.25/rad2as;               // Minimum step for control
r = 1/m2ft;                         // Masses (OTA, counterweights) are at 1 ft from RA axis
m = 2*48/kg2lb;                     // 48 lbs plus counterweights
Jw = m*r^2;                         // Moment of inertia in kg-m^2
omEarth = (15/rad2deg)/3600;        // Nominal angular velocity OTA at equator
dOmega = guideRatio*omEarth;        // Change in angular velocity
t0 = (dTheta/dOmega)/1.25;          // Total pulse time
t1 = 0.1*t0;                        // Time to ramp-up or ramp-down linearly, say 0.1*t0
                                    // (t0 + t1)*dOmega = dTheta, t1 = 0.25*t0
 
// After the gearing
Tl1 = Tl/gearRatio;
dPhi1 = dTheta*gearRatio;
Jw1 = Jw/gearRatio;
dOmega1 = dOmega/gearRatio;
 
micro = 64;
thetaStep = (0.9/micro)/rad2deg;    // Step angle
Sf = 2;                             // Safety factor
A = dPhi1/thetaStep;                // Number of pulses
f2 = A/(t0-t1);                     // Pulse speed
Nm = (thetaStep/(2*%pi))*A*60;      // Revolutions per minute
 
// Microstepping torque vs holding torque
Thold = 0.36;                       // Holding torque
Tmicro = Thold*sin((%pi/2)/micro);
 
Ta = ((J0 + Jw1)/9.55)*Nm/t1;       // Acceleration torque
Tm = (Tl1 + Ta)*Sf;                 // Required torque
 


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

George Cushing
 

Ah, Losmandy rates the G11 at a 60 pound payload. Your average 12" f/4.5 Newt weighs about 45 pounds. CF may knock off a 2-3 pounds, but you are still pushing the mount's limits.

Additionally, as we say at the yacht club that boat has a a lot of windage. The 50"+ length and 14"+ height of the optical tube has to be considered when evaluating the capacity of a mount. 


Re: Focuser for MaxEsp3

Seven Jones
 

On Wed, Jul 21, 2021 at 09:26 PM, Ken Hunter wrote:
You can caarefully cut away the connecter, unsolder the pins 1 at a time and install the pins like I did in my build.

That's how I'm gonna do it.
What are the plug on your board? As far as I know also the small screw terminals also fit?


Re: Thanks OnStep - Results from a recent project using a G11 OnStep Mount

Chad Gray
 

WOW!  Beautiful!


On Fri, Jul 23, 2021 at 12:08 AM Rockmover <kruse@...> wrote:
I just wanted to post a recent project that was made possible by both OnStep, and all the help from these message boards.

Unfortunately, due to work, my astronomy time has been limited the last 6 months.  However, my buddy who shares our remote observatory has been taking great advantage of the G11 OnStep mount, and a small Stelavue 80 mm scope setup we have.  
 
https://www.astrobin.com/7381yd/

IC 2177 - Seagull Nebula, 






            StockCarMafia


Thanks OnStep - Results from a recent project using a G11 OnStep Mount

Rockmover
 

I just wanted to post a recent project that was made possible by both OnStep, and all the help from these message boards.

Unfortunately, due to work, my astronomy time has been limited the last 6 months.  However, my buddy who shares our remote observatory has been taking great advantage of the G11 OnStep mount, and a small Stelavue 80 mm scope setup we have.  
 
https://www.astrobin.com/7381yd/

IC 2177 - Seagull Nebula, 






            StockCarMafia


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

Henk Aling
 

On Thu, Jul 22, 2021 at 09:06 PM, Mike Ahner wrote:
On Thu, Jul 22, 2021 at 07:13 PM, Henk Aling wrote:
I would like to understand the effect on tracking accuracy.
Maybe start here:
main@onstep.groups.io | Wiki
I know that link well, it doesn't say anything about Vref for the TMC2130.

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