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Re: Celestron CGE

Khalid Baheyeldin
 

On Tue, Dec 24, 2019 at 10:08 PM, fetoma wrote:
I plugged 10:1 into the spreadsheet and this is the best I could get in resolution between 5:1, 15:1, and 20:1.
This 10:1 precision planetary has enough torque, but will require either the S109 driver, or the TMC5160 driver.

All of these geared motors are 200 step, not 400 step though. So enter that into the first column.
Second, you are not limit to 1/16 microstep. You can use 1/32, or even 1/64, so enter that in the second column.
Then enter 3.0 degree per second (a reasonable speed), or even 2.5 deg/sec.

The new spreadsheet just lists the maximum and minimum of uSecond/Step, but does not say what the middle point is.
Anyway, with S109 and either of the STM32/MiniPCB/MaxPCB, you can have a different microsteps for slewing.


Re: Celestron CGE

fetoma
 

I plugged 10:1 into the spreadsheet and this is the best I could get in resolution between 5:1, 15:1, and 20:1.


Re: Celestron CGE

Khalid Baheyeldin
 

On Tue, Dec 24, 2019 at 06:55 PM, John Scherer wrote:
Simingx's mount build is exceptional.  He's using a type of gearbox called Harmonic Drive.  Not super common, especially smaller than nema 23, but they have very low to non-existent backlash.  Much harder to put this into a CGE ;-). 
No (and Yes).

Yes, Simingx's scope uses Harmonic drives, but he is driving them with a regular motor that has a built in gearbox.
Specifically, it is this motor from Stepper Online.
If he was using the harmonic drives on their own, then what you said wold be true.
But he is not, so, if there is backlash or whatever other drawbacks, they would show up. If they did, they were minor.
His photos have been amazing.

I do have a motor that has and 18:1 gear box. And that is not planetary, it is just spur gear (not planetary).
There is backlash, but 1 to 2 arc minutes tops, and that did not stop me from taking unguided long exposures.
But this is a made in Japan motor (don't know about the gearbox, probably the same), and it is not the same as Stepper Online ones, so don't want to generalize too much.

All that led me to say that geared motors are not as bad as they are though to be.

Klaus's system is a beauty.  I really like his Newtonian, the TS-Photon with Carbon Fiber tube.
Again, the motors have gearboxes.

I didn't want to imply that gearbox drive was somehow inherently bad, just that getting a good one (something with lower backlash or periodic error) can be hard with volume produced Chinese imported motors with a cheap gearbox installed.  A well made planetary gearbox can be wonderful but I don't know how well the imports are QC'd, so luck of the draw to some extent.
Yes, there will be variation. Even my Japan motors have variation in the amount of backlash for each axis.

But the above examples show that all this is not an issue. If you are autoguiding, PHD2 will take care of the backlash.
I did start doing autoguiding, but I was out only a few times, so can't emphatically state how well it works yet.


Re: Celestron CGE

John Scherer
 

Simingx's mount build is exceptional.  He's using a type of gearbox called Harmonic Drive.  Not super common, especially smaller than nema 23, but they have very low to non-existent backlash.  Much harder to put this into a CGE ;-).  Klaus's system is a beauty.  I really like his Newtonian, the TS-Photon with Carbon Fiber tube.

I didn't want to imply that gearbox drive was somehow inherently bad, just that getting a good one (something with lower backlash or periodic error) can be hard with volume produced Chinese imported motors with a cheap gearbox installed.  A well made planetary gearbox can be wonderful but I don't know how well the imports are QC'd, so luck of the draw to some extent.

In the end, converting a telescope mount to Onstep is always unique in some way, and always an exercise in trade-offs.


Re: Introduction and some help

Dave Schwartz
 

It's really a matter of experimentation. You should have received a data sheet with your motors that identifies the wires that make up the connections to each coil. If not, it's easy to identify the pairs with an ohmmeter. Connecting to the driver is also trial and error. Since different drivers assign the pins differently, just try a few combinations until it works. As long as you have Vref set below you motor's maximum current, you can't hurt anything.


On December 24, 2019 11:00:34 AM EST, Grant Baxter <grant.lynne.baxter@...> wrote:

Hi Dave

Thanks for the info, really appreciate it. If I understand it correctly, the RJ45 connector is an 8 pin, and in this instance, bridged to essentially a 4 pin. 

In terms of wiring, my stepper motors have 4 wires: red, black, blue and green - which wire goes to which pin pairing?

Regards

Grant


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


Re: Celestron CGE

Khalid Baheyeldin
 

On Tue, Dec 24, 2019 at 12:21 PM, tnut55 wrote:
A 5:1 planetary reducer, a 1:1 belt with the native 1:180 worm wheel reduction seems reasonable to me.
You could go a bit more on the reduction.

Keep the belt at 1:1, but go with a motor with either 10:1 or 15:1 reduction.
That makes the motors work considerably less for more torque.
Also increases the resolution.

Note that people have used geared motors with great success.

For example, see simingx's custom mount: it has a 30:1 geared motor.
Or Klaus's Fornax 52 with 10.8:1 geared motors.

And quality commercial mounts have been using geared motors.
Examples: the Vixen MT-4 motor for the GPDX, and the geared brushless motors on the Vixen SXD, just to name two that I owned.

The worries about backlash are real, but I think they are often exaggerated. At least that is true for high quality low periodic error worm gears.


Re: Celestron CGE

tnut55
 

Yes, there are 3 CGE conversions in the showcase.  All use belt drive but I don't think any are 1:1.

A 5:1 planetary reducer, a 1:1 belt with the native 1:180 worm wheel reduction seems reasonable to me.


On Tue, Dec 24, 2019 at 10:13 AM, fetoma
<fetoma@...> wrote:
Alex and John, have you seen the showcase page with the already belt driven converted CGE's?


Re: Characterizing NEMA17 stepper motor/driver micro-stepping accuracy

Howard Dutton
 

There is now a Wiki page that covers this topic, I welcome comments and corrections, this is my best understanding of the subject:
https://onstep.groups.io/g/main/wiki/Stepper-Motor-Accuracy

I am not done testing motors but have finished with the 1.7A 0.9° NEMA17 for now I think.  Next will be the 0.85A 0.9° NEMA17 PKP244MD08 which is really more interesting to me since that's what my G11 uses.


Re: Celestron CGE

fetoma
 

Alex and John, have you seen the showcase page with the already belt driven converted CGE's?


Re: Introduction and some help

Grant Baxter
 

Hi Dave

Thanks for the info, really appreciate it. If I understand it correctly, the RJ45 connector is an 8 pin, and in this instance, bridged to essentially a 4 pin. 

In terms of wiring, my stepper motors have 4 wires: red, black, blue and green - which wire goes to which pin pairing?

Regards

Grant


Re: Introduction and some help

Dave Schwartz
 

The sockets on the STM32 PCB are RJ45, with each pair of pins (1-2, 3-4, 5-6, 7-8) connected by the PCB. The interconnection is done to increase both current carrying capacity and robustness of the connection. What I have done is use an inexpensive RJ45 breakout board, with RJ45 socket on it, and connect the motor wires into it - bridging the same wires that are doubled at the PCB end. The breakout board then gets hot-glued somewhere on the mount or motor bracket and I use standard RJ45 ethernet cables.

Some people do not use the RJ45 on the PCB and wire 4-pin aviation connectors directly to the header by the drivers (that's what they are there for) and use another aviation connector at the motor end. Then you get to make your own cables.

Pictures of both are available in the message history through a search.

On 2019-12-24 8:47 a.m., Grant Baxter wrote:
The motorizing of the mount is progressing, albeit slowly. The stepper motors have arrived (Nema 17 400 step, 0.9 degree, 0.9 A) and I have ordered the onstep STM32 unit. Am now want to sort out the cabling from the controllers to the motors - as I understand it, the cable connectors on the STM32 are RJ45 connectors and the motor end of the cable is RJ11, so 2 questions please:

firstly - can I connect a male RJ45 connector to a male RJ11 connector? If so, what is the wiring diagram?  Secondly, what type of cable should I be using? Am assuming it will be a 4 core cable sufficient to carry the 0.9A? Or are there other considerations - for example - maximum length of the cable etc?

Thanks for the guidance

Regards

Grant


Re: Buying an EQ5

Prasad
 
Edited

 
Vixen worm shaft extended on both sides and so, it may be broken only on one end. Since it is a Dec shaft you may still be able to use the mount. RA shaft damage may give you excessive PEC but Dec shaft damage is not consequential IMO.

Added during edit:
A Vixen GP mount is greatly superior in quality to Bresser (or any China made) mount. I have both Vixen GP & SP as well as Bresser EXOS2 and I am stating my experience. 
 
 
 

On Tuesday, December 24, 2019, 08:14:43 AM EST, julianporter5@... <julianporter5@...> wrote:
 
 

[Edited Message Follows]

What is the quality like of a Bresser Mon2 eq Mount

I've seen a Vixen Great Polaris but the end of the declination worm gear shaft has sheared. This begs the question whether there is other damage to the gear. Where would I find a replacement worm gear?


Re: Introduction and some help

Grant Baxter
 

The motorizing of the mount is progressing, albeit slowly. The stepper motors have arrived (Nema 17 400 step, 0.9 degree, 0.9 A) and I have ordered the onstep STM32 unit. Am now want to sort out the cabling from the controllers to the motors - as I understand it, the cable connectors on the STM32 are RJ45 connectors and the motor end of the cable is RJ11, so 2 questions please: 

firstly - can I connect a male RJ45 connector to a male RJ11 connector? If so, what is the wiring diagram?  Secondly, what type of cable should I be using? Am assuming it will be a 4 core cable sufficient to carry the 0.9A? Or are there other considerations - for example - maximum length of the cable etc?

Thanks for the guidance

Regards

Grant


Re: Buying an EQ5

julianporter5@...
 
Edited

What is the quality like of a Bresser Mon2 eq Mount

I've seen a Vixen Great Polaris but the end of the declination worm gear shaft has sheared. This begs the question whether there is other damage to the gear. Where would I find a replacement worm gear?


Re: Celestron CGE

John Scherer
 
Edited

While I don’t own a CGE Mount, I wouldn’t exclude belt drive without some testing. You gain torque and by not using a gearbox, you reduce the likelihood of backlash, which can be significant depending on how lucky you get with the motor/gearbox purchase.   I'm doing a 4:1 belt drive with my Losmandy GM-8.


Re: Celestron CGE

Alexander Varakin
 

I am getting a CGE too with the purpose of converting it to Onstep.
I believe that belt drive provides better accuracy so I think that planetary gears would work for visual work, but for AP it is worth the effort to have a belt drive.

Alex


Re: Characterizing NEMA17 stepper motor/driver micro-stepping accuracy

Howard Dutton
 

And the last (for tonight) is the S109 running the motor at 2.32A:


Re: how enter telescope position manually

Khalid Baheyeldin
 

On Mon, Dec 23, 2019 at 06:38 PM, Dan Sawyer wrote:
Is it possible to enter onstep scope Dec and RA coordinates manually?
Do you mean ask it to slew to an RA/DEC combo, or tell it that it is pointing to a certain RA/DEC combo?

Both are possible, though I assume that you mean the latter, so you can polar align indirectly.

For the first (slew to coordinates), you can use the Android App, select Enter Coordinates, then fill in the values, and OnStep will slew to that place.

For the latter (set coordinates manually), Sync is the function you need, but it is tricky in that to Sync, you need an object to sync on.
If you use a planetarium, you can go to the zenith, then Sync on that point.

I am able to do it from KStars, though other planetariums probably can do the same.

I tried Stellarium Mobile Plus, and it does not have this function when I click the nearest star to the zenith, only Goto. Maybe Sky Safari can do it?

Since your goal is polar alignment, checkout the Refine PA function, which is documented under the Advanced page on the Wiki. Maybe it is all you need.


Re: SkyWatcher14- Debug help please

DaveGee
 

G'day,

I did a couple of things
- corrected an error in my StepsPerDegree (oops!)
- changed MaxAzm to 360
- reversed the direction of the Az motor
uploaded the code to the Teensy

And rebooted my phone and... Sensible slews achieved.  Yay!

Now all I need for all this smoke to disappear and try it out under some stars.

I have a video of the rig slewing on by FB profile...
https://www.facebook.com/profile.php?id=100011497001381

--
Regards
DaveGee
www.kuriwaobservatory.com


Re: Characterizing NEMA17 stepper motor/driver micro-stepping accuracy

Howard Dutton
 
Edited

Now the LV8729 at 0.96A (40% power,) I will not test above this setting for this motor since the driver can't reach 1.7A  My plan is to test at 40%, 70.7%, and 100% power where possible.