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

John Scherer
 

Can’t wait to see these results Howard
Re: Characterizing NEMA17 stepper motor/driver micro-stepping accuracy

Howard Dutton
 
Edited

Here's another chart where i picked data to match the angular range, scale, and style of the Hackaday article.  It's easy to see this motor/driver is more accurate than any of the ones they tested:
Re: Characterizing NEMA17 stepper motor/driver micro-stepping accuracy

Howard Dutton
 
Edited

Here's the form I plan to present the data in.

This example is just the "unloaded" data, I still need to get my weights measured/established before doing the other measurements for this motor.  Note the "unloaded" data was used for 8 and 16 oz-in also.
Re: Characterizing NEMA17 stepper motor/driver micro-stepping accuracy

Howard Dutton
 

Here's the CAD of my test fixture, this is already printed and working (including a slightly hacked OnStep software stack to gather data.)  My 200K count Gurley encoder goes on one side and the stepper motor under test on the other.  A nylon cord supports the weight to place a load on the stepper motor shaft.  The pulley has a 2" radius so the torque load (oz-in) = weight (oz) x 2. The encoder accuracy (+/- 6.5 arc-seconds) is easily sufficient to provide relevant results for this test.
Characterizing NEMA17 stepper motor/driver micro-stepping accuracy

Howard Dutton
 
Edited

I would like to expand on the information presented in this useful article: "How Accurate Is Microstepping Really?" to include a wider range of stepper motors, stepper drivers, drive currents, decay modes, and torque loads.

The prior results were taken for a NEMA17 1.8°/step motor unloaded and loaded with 1000 gm-cm (13.9 oz-in) which I'm guessing (and this needs to be measured) is perhaps 2x or 4x what it takes to for example move my G11 around, depending on how out of balance it is and what angle the axes are at.  The mere fact that this (13.9 oz-in) load can cause an angular displacement of 1° implies that my G11 might see 0.25 to 0.5° of shaft angular displacement with a similar stepper motor.  My G11, however, has 0.9°/step motors so hopefully we can again cut that estimate in half for 0.125 to 0.25°.  Take the average of that 0.187° and /360 (360t wheel gears) to arrive at a displacement of 1.87 arc-seconds.  We already know these motors work fairly well so I suppose the RA axis movement is responsive enough for auto-guiding to get the job done even with that "soft" magnetic field pulling the rotor along.  The Dec axis behavior while guiding is more concerning to me since a change in direction will need 2x 1.87 arc-seconds to start pushing in the opposite direction and even then it has to overcome stiction (friction holding against the start of movement.)  This is why I suspect better performance is possible than that provided by simply using 400 step motors directly driving the worms.  Other drive designs using more overall reduction amplify torque and so lessen the stepper motor load and these concerns along with it, while potentially introducing other troubles.

I wonder...
1. How uniform is micro-stepping with the drivers we use?
2. Are 0.9°/step motors really twice as accurate as 1.8°/step motors?
3. Are 0.36°/step motors even more accurate?
4. How will a MKS Servo stepper motor perform?
5. How do stepper motor drive current and shaft angular displacement relate, is it a linear relationship?
6. Does TMC spreadCycle vs. stealthChop modes make any difference WRT accuracy?
Re: Microsteps slewing with ramps1.4 A4988

julianporter5@...
 

I’ve had a look at the wiki about correcting for alignment errors using the Refine Polar Alignmenf function in the Android app. I know I’m going to have large pointing errors as I don’t have a polar scope and am aligning using a laser. Will the correction function work with large errors of the order of a few degrees? 
Re: Flashing STM32 and WEMOS

Dave Schwartz
 

Correct. This is as designed. It is because the supply voltages and grounds, being derived from two different sources (one being the PCB supply via the DC-to-DC regulator, the other being via the PC power supply via the USB), have a high probability of conflicting and thus causing an immediate release of the magic smoke that electronic devices run on. The result is permanent destruction... been there, done that.

That is why you never use the STM32's onboard USB when it is plugged into the circuit board. The rules for doing it safely are so limited that it is likely that almost everyone would blow theirs up at some point so it was much safer to say 'never, never' and provide an external data-only USB adapter (the CP2102) which does not connect the USB power to the regulator power. Yes... it was done on purpose.

However, there have been at least two cases of people unable to communicate with the STM32 over the CP2102. This is because they used any old USB cable they had at hand and happened to have grabbed a power-only USB cable, which then resulted in no connections at all. Yes, there are power-only USB cables out there... some manufacturers who sell devices that only need to charge via USB and not communicate data save a few cents on their cost by leaving out those two wires. A case in point: many wireless headsets come with cables like this.

On 2019-12-23 8:22 a.m., tnut55 via Groups.Io wrote:
You should be getting +5v from the regulator board to the STM32 if I read the circuit board right on the easyeda site.



On Mon, Dec 23, 2019 at 2:54 AM, helmutliebenau@...
<helmutliebenau@...> wrote:
If I look on the PCB I only see an connection from CP2102 to STM32
(TX,RX). And GND of course. That means the plugged STM32 have no
power supply (3,3V or 5V) from the CP2102. But power supply for
flashing is needed, isn't?
In the assambly instruction (very helpfull) I read:*Although
already covered in the Wiki, do NOT , ever , ever , connect a USB
cable to*
*the USB port on the STM32 module while it is installed in a
powered PCB - doing so will cause*
*immediate destruction of your STM32 module .

*But in this video https://www.youtube.com/watch?v=mfJhx_XDzBk I
see both is connected to the PCB (USB cabel via CP2102 + power
supply via LM2596).
Maybe this is my problem. I have connect both to the PCB for
flashing. I am not sure about this.
Re: Flashing STM32 and WEMOS

tnut55
 

You should be getting +5v from the regulator board to the STM32 if I read the circuit board right on the easyeda site.



On Mon, Dec 23, 2019 at 2:54 AM, helmutliebenau@...
<helmutliebenau@...> wrote:
If I look on the PCB I only see an connection from CP2102 to STM32 (TX,RX). And GND of course. That means the plugged STM32 have no power supply (3,3V or 5V) from the CP2102. But power supply for flashing is needed, isn't?
In the assambly instruction (very helpfull) I read: Although already covered in the Wiki, do NOT , ever , ever , connect a USB cable to
the USB port on the STM32 module while it is installed in a powered PCB - doing so will cause
immediate destruction of your STM32 module .

But in this video https://www.youtube.com/watch?v=mfJhx_XDzBk I see both is connected to the PCB (USB cabel via CP2102 + power supply via LM2596).
Maybe this is my problem. I have connect both to the PCB for flashing. I am not sure about this.
Re: Stepper motor mount for Losmandy GM-8

Howard Dutton
 

Nicely done John.
Re: Flashing STM32 and WEMOS

helmutliebenau@...
 

If I look on the PCB I only see an connection from CP2102 to STM32 (TX,RX). And GND of course. That means the plugged STM32 have no power supply (3,3V or 5V) from the CP2102. But power supply for flashing is needed, isn't?
In the assambly instruction (very helpfull) I read: Although already covered in the Wiki, do NOT , ever , ever , connect a USB cable to
the USB port on the STM32 module while it is installed in a powered PCB - doing so will cause
immediate destruction of your STM32 module .

But in this video https://www.youtube.com/watch?v=mfJhx_XDzBk I see both is connected to the PCB (USB cabel via CP2102 + power supply via LM2596).
Maybe this is my problem. I have connect both to the PCB for flashing. I am not sure about this.
Re: ci700

--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
Celestron CGE

fetoma
 

I posted a few post down about this but wanted to start a new thread. What I would like to do is provide all CGE owners an option to keep their mounts when the electronics die. I found this group by stumbling upon it while looking for a fix for my CGE. I was pretty angry that I spent over $2K for a great mount that had it's motors and motor control board replacement parts extremely expensive and now obsolete. In reading many posts for the past week, I've come to the conclusion that I would like to be the guinea pig to something CGE owners can use without throwing away their mounts. My goal would be to do this with little modification to the mount itself, and I think it can be done with just a modification of the motor/worm block. I could just mimic jean-francois.harvey's mod, or even Marko Himelreich's mod, but I want to lean towards a 1:1 belt/pulley drive. Kahlid had mentioned a Nema 17 motor with a 10:1 high precision planetary gearbox (17HS15-0404S-HG10) that should fit. I would like to have excellent tracking and incorporate the DEC and RA switches also if possible. With all that said, I would like to hear some opinions on motor selection along the lines of Kahlid's motor above to settle on a motor, and which main controller would be best to use to possibly future proof the mount.

Thanks,
Frank

 
Re: Stepper motor mount for Losmandy GM-8

John Scherer
 

Did a 3D print of my 4:1 stepper mount for the GM8 mount.  It’s printed in PETG and came out pretty good. 
Re: Inexpensive Replacement for the MiniPCB's OKI78SR5/1.5W36C Power Regulator

simingx@...
 

Do note that their maximum input voltage is 28V as compared to 36V for the Murata units. 
Re: Flashing STM32 and WEMOS

Khalid Baheyeldin
 

On Sun, Dec 22, 2019 at 04:41 PM, tnut55 wrote:
 
At least you know that the STM BP and CP2012 work.  That says the problem is on the board somewhere.
Or components on the board, such as the female headers.

I'd start with making sure the slide switch is correctly setting the boot0+ if you are getting failed to init error messages.
This is easy to rule out. Just disconnect the wires going from the slide switch to the headers on the STM32, and use the jumper that came with the STM32 itself. We know that latter one works because he tested it standalone.
Re: Flashing STM32 and WEMOS

tnut55
 

I can't help you there.  I have not built my STM32 board yet but I have constructed both the mini and max

At least you know that the STM BP and CP2012 work.  That says the problem is on the board somewhere.

I'd start with making sure the slide switch is correctly setting the boot0+ if you are getting failed to init error messages.


On Sun, Dec 22, 2019 at 3:07 PM, helmutliebenau@...
<helmutliebenau@...> wrote:
The STM32 flashing works as following (at least in my case). The STM32 Board has to unplugged from the PCB. Then the CP2102 has to connected with the STM32 directly. This pins has to connected together (TX,RX, GND, 3,3V). The jumper Boot 0 has to moved on the + side. Then connect the USB cable with the CP2102 and the flashing works.
I don't no why the flashing with plugged STM32 doesn't work. I am using the PCB OnStep STM32 V1.8.

Re: Flashing STM32 and WEMOS

Khalid Baheyeldin
 

On Sun, Dec 22, 2019 at 04:07 PM, <helmutliebenau@...> wrote:
don't no why the flashing with plugged STM32 doesn't work. I am using the PCB OnStep STM32 V1.8.
Using a magnifying lens, look for solder bridges between adjacent pins on the female headers.
Or solder bridges on the PCB itself.

Then, with all power disconnected, test continuity between each two adjacent pins, using a multimeter's Ohm selection or audible connectivity function.
Re: Flashing STM32 and WEMOS

helmutliebenau@...
 

The STM32 flashing works as following (at least in my case). The STM32 Board has to unplugged from the PCB. Then the CP2102 has to connected with the STM32 directly. This pins has to connected together (TX,RX, GND, 3,3V). The jumper Boot 0 has to moved on the + side. Then connect the USB cable with the CP2102 and the flashing works.
I don't no why the flashing with plugged STM32 doesn't work. I am using the PCB OnStep STM32 V1.8.
Re: Encoders

--Oz--
 

So comparing these two options are not very different in price:

1. $14 stepper motor and $15 tmc5160 drivers = $29,
2. $33 MKS-SERVO42B-Nema17-Closed-Loop-Stepper (the link I posted above to BG site),

I am seeing not much price difference, has it been tested the difference in preformance in our application?
Re: Stepper motor mount for Losmandy GM-8

Alexander Varakin
 

I used 400 steps NEMA 23 for my GM8 with direct drive using spring coupler.
Here is the motor:
29841 - 29860 of 44715