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ci700

--Oz--
 

I am looking to buy the stm32 Kit C to use on my ci700 that has Gemini servo motors with 250ppr encoders and the arduino pro mini (with https://github.com/misan/dcservo) with A4950 motor drivers. This setup would be 180t * 25 * 250 * 4 = 4,500,000 ticks for turn (half of the G11/Gemini setup), I am guessing that is ok.

Few questions:
1. for the arduino pro mini, should I order the 3V or 5V version to use with the bluepill stm32?

If I decide to use stepper motors, looks like one guy used nema 17 (17HS4401) and 16t/40t pulleys with belts, where do i find these parts (links):
2. Motors? 
3. belts/pulleys?

4. What stepper motor driver is most recommended (LV8729)?
5. If you dont have BHC or the SHC, how do you control the mount (align-stars/goto/etc)?

6. Looks like the SHC PCB is not sold anymore, (https://baheyeldin.com/astronomy/onstep-esp32-smart-hand-controller-shc.html),  Is there a schematic somewhere?

TIA!

simingx@...
 

I'll try:
2) https://www.omc-stepperonline.com/
3) Ebay / Aliexpress
4) TMC2130 et al, but read the FAQ
5) Android app, Kstars, Sky Planetarium, etc

Dave Schwartz
 

On 2019-12-16 12:35 a.m., --Oz-- via Groups.Io wrote:

6. Looks like the SHC PCB is not sold anymore, (https://baheyeldin.com/astronomy/onstep-esp32-smart-hand-controller-shc.html), Is there a schematic somewhere? <https://baheyeldin.com/astronomy/onstep-esp32-smart-hand-controller-shc.html>
https://easyeda.com/dschwartz/onstep-shc

Khalid Baheyeldin
 
Edited

On Mon, Dec 16, 2019 at 12:35 AM, --Oz-- wrote:
I am looking to buy the stm32 Kit C to use on my ci700 that has Gemini servo motors with 250ppr encoders and the arduino pro mini (with https://github.com/misan/dcservo) with A4950 motor drivers. This setup would be 180t * 25 * 250 * 4 = 4,500,000 ticks for turn (half of the G11/Gemini setup), I am guessing that is ok.

Few questions:
1. for the arduino pro mini, should I order the 3V or 5V version to use with the bluepill stm32?
Retaining the servos is possible, but before you embark on this, consider the challenges:

1. Rarity: I only know of one person (German or Austrian?) who have made it work a few years back. There was possibly another person asking questions (Asia), but not sure if he actually implemented it or not. On the other hand, we have hundreds of people using stepper motor setups.

2. Complexity: you require two additional microcontrollers, one for each servo motor, and additional firmware on them.

3. Tuning: you need to do the PID thing described in dcservo's documentation and Youtube videos.

Based on the above, I think that you are better off with just stepper motors, like the vast majority of OnStep users. Ignore the encoders.

If I decide to use stepper motors, looks like one guy used nema 17 (17HS4401) and 16t/40t pulleys with belts, where do i find these parts (links):
2. Motors? 
Read the entire Construction page. It has lots of helpful links.
Use the spreadsheet on the construction page to run the numbers.

OMC Stepper, as simingx said. Also eBay and AliExpress.

Motors that are 0.9 degree are better, and they should have adequate holding torque (36 Ncm or more), and low inductance.

This 0.9 degree, 0.9A motor is popular with EQ5 mounts.
With sufficient reduction (3:1), it should be able to drive CI700 (G11 like mount)

An alternative approach is to get a motor with an integrated gearbox with more reduction (e.g. 10:1 to 15:1).
That way, you can use 1:1 pulleys with a lesser number of teeth (e.g. 25T to 25T), so they are easier to fit on the worm shaft side.
With the added benefit that the reduction increases resolution and torque at the same time.
Again, run the numbers in the spreadsheet.

3. belts/pulleys?
eBay or AliExpress. Also Amazon.
The Construction page has belt size calculators, ...etc.

4. What stepper motor driver is most recommended (LV8729)?
Depends on the motor current.
If it is low (1A or less) then LV8729 will work well, and the TMC2130.
If it is above 1A, then you need the S109 or the TMC5160.

Again available on AliExpress, eBay and Amazon.

5. If you dont have BHC or the SHC, how do you control the mount (align-stars/goto/etc)?
The STM32 kit C has a Wemos, which is an ESP8266 and allows full control from an Android App. Very convenient.

--Oz--
 

Wow! Fast and excellent replies, many thanks guys getting me up to speed quickly!!! On to more reading :)

--Oz--
 

Regarding steppers, thanks for the 0.9 degree motors! I have never seen these before (only down to 1.8 degree), but I don't play with them much.
You mention low inductance. Since the ci700 is a step above the cge/lxd75 mounts in terms of payload weight capability, I figure go slightly larger (only a couple bucks more each, same size and only 8mm longer).
If you look at the comparisons, the slightly larger one has 1/3rd the inductance/resistance and about twice the current.

But what I am not sure is the voltage, the one you pointed out is 5.4v, but I am thinking your running them at 12v, correct?
The lower inductance is rated at 2.8v, would this work at 5V or 12V? (I have many 5/12V power supplies already and buck converts to get any voltage).
Motors here:
https://www.omc-stepperonline.com/nema-17-stepper-motor/nema-17-bipolar-0-9deg-36ncm-51oz-in-0-9a-5-4v-42x42x40mm-4-wires.html
https://www.omc-stepperonline.com/Dual-Shaft-Nema-17-Bipolar-09deg-44Ncm-6248ozin-168A-28V-42x42x48mm-4-Wires.html?search=Nema%2017%20Bipolar%200.9deg

simingx@...
 

The stepper motor drivers Onstep uses are "chopper" type, meaning they operate the motor in somewhat "constant current" mode.
So, the rated voltage of the motor is not significant for us, in fact the higher the supply voltage is in relation to the motor voltage, the better. Low inductance (from the low voltage / high current rating) lets us run the motor at higher speed as the supply is more able to "drive" the coils to change their magnetic polarity. 
In any case, the 1.68A motors will be better (as long as your motor drivers can handle them) as you can have higher slew rates. My mount does 2.9 deg/s into a 2400:1 reduction at 24V. 

--Oz--
 

@ simingx@...
2:41am   
Thanks, perfect info. Its sorta sad with 4 decades of electric motor use (mostly racing), I dont have much stepper motor experience.
I see microstep rates upto 256, generally, what rates are you guys using? 
Or is it the highest rating your driver can provide or even if you have a 256 driver you run it at some lower microstep setting or with testing you find the sweet spot (mount/gearing/motor/voltage) of speed and smoothness?

I do know about low inductance and higher voltage :) , In this project, I got a 3mm magnet ball to spin 3.8Mrpm https://www.youtube.com/watch?v=ZQE05T-3680
Of course the next day testing I get to  3,808,800 RPM, 63,480 RPS, 1338mph, 2153kph, 24.3M G's

Khalid Baheyeldin
 

The rated voltage of the motor is not the voltage it will be run at.
Most people run the motors at 12V despite them being rated for much less than that.
Some run them at 24V for bit better performance, but they have to use a transformer from 12V battery to 24V.
The lower the voltage the motor is rated for, the better (provided it is low inductance, and sufficient current).

Regarding current, more current is not necessarily good. More current means more heat dissipation.
The lowest current that will do the job is best.
That is why the 0.9A motor is preferred, because it can be run with the LV8729 which almost has no heat dissipation, and therefore no need for a fan in the controller.

Usually people run the stepper drivers at 1/16 or 1/32.
Almost no one runs at 128 or 256, for torque reasons and angle accuracy reasons.
So ignore what the specific driver can go down to regarding microstepping.
Stay with the 4 models I mentioned (2 for low current LV8729 and TMC2130, 2 for higher current S109 and TMC5160).
Ignore all other models, since they are either dated, or have limitations.

If you are autoguiding, then that will take care of any small errors, whether in the gears or elsewhere, so everything works out regardless.

Khalid Baheyeldin
 

On Wed, Dec 18, 2019 at 05:41 AM, <simingx@...> wrote:
In any case, the 1.68A motors will be better (as long as your motor drivers can handle them) as you can have higher slew rates. My mount does 2.9 deg/s into a 2400:1 reduction at 24V. 
Current is not the only factor.
Gear reduction plays an important role.

For example, my mount has a 180:1 wheel.
The motors I use have an integrated 18:1 gearbox, so overall 3240:1 reduction.

I can do 2.9 deg/sec despite the motors being tiny NEMA 11, and I run them at 0.65A and 12V.

And all that is with the STM32, and microsteps goto of 1/4, while tracking is 1/16.

That is why I recommended 10:1 or 15:1 geared NEMA17 motors. More reduction is better (up to a point).

Howard Dutton
 

On Wed, Dec 18, 2019 at 09:48 AM, Khalid Baheyeldin wrote:
Almost no one runs at 128 or 256, for torque reasons and angle accuracy reasons.
Almost everyone running the TMC5160, 2130, 2209, 2208, and 2100 takes advantage of 256x mode since the driver automatically interpolates lower modes to 256x for smooth vibration free motion.

George Cushing
 

Yes, A4988s can be had for $0.50 and DVR8825s for around a buck, but TCM2130s and LV8729s are only a few dollars more. Probably not the place you want to cut corners. You can lose most of the connectors on the STM32 and just solder things to it. Save a little and avoid corrosion/continuity problems in the future.

--Oz--
 

I ordered a couple days ago the stm32 blue pill kit-C, but havent seen a email to pay for it. I am not in a hurry, just wondering.

On a side note, where to find the lowest cost TMC5160 drivers? (anyone, link plz, tia!).

Khalid Baheyeldin
 

On Wed, Dec 18, 2019 at 03:38 PM, George Cushing wrote:
Yes, A4988s can be had for $0.50
The A4988 is an OK performer (no vibration), but being limited to 1/16 max, it is less flexible. If you need 1/32 (per the spreadsheet), you are out of luck. As you say, there are better options out there, for not too much money.

and DVR8825s for around a buck
The DRV8825 used to have an advantage in that it can drive more current for more torque.
But it is notoriously shaky, and inaccurate too.
No one should use it for new builds.

Khalid Baheyeldin
 

On Fri, Dec 20, 2019 at 12:49 AM, --Oz-- wrote:
On a side note, where to find the lowest cost TMC5160 drivers? (anyone, link plz, tia!).
They are relatively new, so the price has not dropped much yet.

Here is the cheapest eBay listing that I can find, for now.
You can also try AliExpress.

Khalid Baheyeldin
 

On Wed, Dec 18, 2019 at 02:22 PM, Howard Dutton wrote:
On Wed, Dec 18, 2019 at 09:48 AM, Khalid Baheyeldin wrote:
Almost no one runs at 128 or 256, for torque reasons and angle accuracy reasons.
Almost everyone running the TMC5160, 2130, 2209, 2208, and 2100 takes advantage of 256x mode since the driver automatically interpolates lower modes to 256x for smooth vibration free motion.
What I meant is specifying 1/256 in the configuration file for OnStep, not interpolation: no one (I know) uses 1/256 for any driver model.

Again and anecdotal observation: I found no practical difference between TMC2130 and LV8729 when testing star trails. No model was better than the other tracking wise. The TMC2130 was quieter for sure, but the LV8729 won because of far less heat dissipation.

As the TMC5160 gets more popular, it could be the driver of choice, since it has all the features:
- high current (if needed)
- 256 interpolation
- low heat dissipation
- configurable from OnStep

Howard Dutton
 
Edited

On Fri, Dec 20, 2019 at 01:03 PM, Khalid Baheyeldin wrote:
What I meant is specifying 1/256 in the configuration file for OnStep, not interpolation: no one (I know) uses 1/256 for any driver model.
For "torque and angle accuracy reasons" you wrote so I figured interpolation applied, at-least somewhat.  And no, they don't do so used often because TMC's can't mode switch [on the fly] and also usually OnStep max steps per degree would be exceeded.  If running my G11 360:1 400 step motors with LV8729's I'd definitely use 128x mode, there is no reason not to.

Howard Dutton
 

On Fri, Dec 20, 2019 at 01:03 PM, Khalid Baheyeldin wrote:
Again and anecdotal observation: I found no practical difference between TMC2130 and LV8729 when testing star trails.
I didn't really find a measurable improvement in tracking with my G11 when switching from a DRV8825 to the TMC2130 either.  And that's at 360:1 where you might actually see it.  Not something like say 3240:1 where the gear reduction makes the motor motion control far less critical.  Perhaps I wasn't looking hard enough though.

No model was better than the other tracking wise. The TMC2130 was quieter for sure, but the LV8729 won because of far less heat dissipation.
Since my four mounts use TMC2100's or TMC2130's (both have similar heat dissipation characteristics) I have to say that this was never an issue for me.  My EM10 mount with the MPJA NEMA11 motors, for example, doesn't even have heat-sinks on the drivers.  The much bigger G11 w/ 0.85A motors worked fine back when its controller had stock heat-sinks on the drivers and they never ran "hot."

--Oz--
 

I found a box of stepper motors:

85x85x66mm 1.8 degree 2.4v 4.5a
56x56x75mm ?? (with driver)
42x42x40mm 1.8 degree 2.8v 2.0A (with encoder / driver)
42x42x23mm 1.8 degree 2.0v 2.0A (with encoder / driver)


The bottom three have some electronics in them, some of the components are:
IRFB4332PbF 42A FET x2
80mΩ current sense resistors x2,
8-Bit Parallel DAC,
ATtiny13 mpu (atmel 0514D),
something that looks like a memory chip (s29al008070tf102) , 
large 270uH inductor plus a couple 47uF caps for LC filter.

If I can't figure out the DB9 connector signals, I could just bypass the electronics and use external driver if needed (but lower 1.8 degree steps).



On Ali I seen this this low cost one (only 32 micro steps)
https://www.aliexpress.com/item/32957327440.html?src=google&src=google&albch=shopping&acnt=494-037-6276&isdl=y&slnk=&plac=&mtctp=&albbt=Google_7_shopping&aff_platform=google&aff_short_key=UneMJZVf&&albagn=888888&albcp=1582410664&albag=59754279756&trgt=743612850714&crea=en32957327440&netw=u&device=c&gclid=Cj0KCQiAxfzvBRCZARIsAGA7YMzfdTVNbAtH6e9YEBCeZfyZyKI7wgOlp247sMTEj76MG5G_P1jpXb4aAp6HEALw_wcB&gclsrc=aw.ds

Tong
 

https://item.taobao.com/item.htm?spm=a1z09.2.0.0.31f62e8dlK2875&id=610106173706&_u=s1lcu5a3bf0
Here is the low-cost TMC5160 for $12. The seller promised me to mail the test product to me on Monday