Question on Torque, Currents, steppers, voltages, CONFIG settings


Guy Brandenburg
 

The problem statement is below.

On my desk and at the telescope making/maintenance/modification workshop at CCCC, and with the considerable amount of generous help of Alan, Ken, and Prasad, I've been playing around with the currents set in my CONFIG file for my TMC5160 steppers on a MaxESP board generously made for us and donated to us by Ken Hunter. I had to increase the current for the two axes to a lot higher than I think some others originally suggested, if I wanted them to do anything more than just track. 

Still have to do some fine tuning of the gears in the mount itself. I wish it weren't so cold out! (Those steppers and the boxes and gears they attach to are safely installed inside the Ealing mount. Way too much of a PITA to take them back out! That's why I soldered up aircraft panel jacks to connect and disconnect the various components.)

The steppers we are using for this bench test are Nema23s, overall length 54 mm, labeled Moon's stepping motors type 23HS2427-01, rev. C 6051225   15/07/04. I so far have not succeeded in finding the specifications for that exact model. Even though part of this ID information looks like a date, I doubt that they have  been in storage for 18 years (ie from July 15, 2004)? I rather doubt it - these look brand new. Something that old, even if in original carton, would acquire some patina. So I can only estimate what they need.

After a number of various settings and trial with these steppers (which are less beefy than the ones we re-installed back at Hopewell Observatory), my settings are as follows:

The voltage on both axes is now 
IHOLD at 500 mA, 
IRUN at 1000 mA, 
IGOTO at 1500 on both axes,
slew base rate is 1.0 degree/second.
slew acceleration distance  is 10 degrees
driver microsteps is 16, and
microsteps goto is 8

Like that, my steppers basically do as they are told by the SHC (go to, etc), except they can't go really fast. Also: 

These steppers have almost no torque at all when they are slewing or being made to guide. 
While, I cannot stop the rotor by hand while it is tracking, I can easily stop the rotors on either axis with my bare thumb and index finger when it is 'guiding' or slewing.

I am considering increasing the voltage to 24VDC; I have a very nice regulated power supply that produces exactly that. However, Ken's board does not have the voltage regulator that is a few cm away from the fuse. I have one that I bought from George. On Ken's board, he just shunted between the two outer legs of the U6 12V regulator. I guess I will  go ahead and try to undo that jumper and solder in the new power supply without destroying other things, I hope. My hands these days have a fair amount of tremor that I cannot control, though I can do very simple soldering by steadying my hands against convenient stationary objects. 

Is the voltage regulator merely recommended here, or required? 

I tried the setup as is, no 12voltage regulator, with the 24VDC power supply for a few minutes, but was afraid of it overheating in some manner, somewhere...

I don't trust my hands all that well to solder in the regulator, and this is our only functioning board.

The ones George sent us still don't work, even after swapping the various major sub-boards with known, functioning ones (such as from Ken's board). 

I guess I need to pack up one of George's boards and go down to the post office and mail it back to him and ask him to trouble-shoot.


Guy Brandenburg, Washington, DC  http://gfbrandenburg.wordpress.com/ http://guysmathastro.wordpress.com/
============================


ghpicard
 

I found the following information on the Brazilian equivalent of eBay, where the seller warns in capital letters that the motors are low torque and not to be used for 3D Printers, CNC, etc...

This is a translation of what's in there:

- Recommended supply voltage: 24V. Operating voltage 12V-36V
- Coil resistance: 0.3 Ohm
- Maximum current: 1.5A
- 200 steps/rev
- Torque 4 Kgf/cm / 0,40 Nm
- Width: 54mm
- Height: 54mm
- Length: 55mm
- Axis length: 25mm
- Axis diameter: 6.35mm

So if you plan to keep this motors it seems that you will need to try going up with VMOT up to 24V and see how they behave but it is probable that the difference will not be very noticeable. They have lower torque than a run-of-the-mill NEMA 17 commonly used for a homemade DIY 3D Printer.
Also, the 12V regulator is optional , and only needed if you have focuser and/or rotator drivers and those drivers cannot withstand the input voltage you use for the board, which in this case would be 24V. You can find this information on the wiki page of the board you are using. This is an example: https://onstep.groups.io/g/main/wiki/26597


Guy Brandenburg
 

Thanks so much for that information!! That’s what get from buying the cheapest steppers I could find.
The ones on the mount are stronger.
Guy

 I found the following information on the Brazilian equivalent of eBay, where the seller warns in capital letters that the motors are low torque and not to be used for 3D Printers, CNC, etc...

“This is a translation of what's in there:

“ - Recommended supply voltage: 24V. Operating voltage 12V-36V
- Coil resistance: 0.3 Ohm
- Maximum current: 1.5A
- 200 steps/rev
- Torque 4 Kgf/cm / 0,40 Nm
- Width: 54mm
- Height: 54mm
- Length: 55mm
- Axis length: 25mm
- Axis diameter: 6.35mm

“So if you plan to keep this motors it seems that you will need to try going up with VMOT up to 24V and see how they behave but it is probable that the difference will not be very noticeable. They have lower torque than a run-of-the-mill NEMA 17 commonly used for a homemade DIY 3D Printer.
“Also, the 12V regulator is optional , and only needed if you have focuser and/or rotator drivers and those drivers cannot withstand the input voltage you use for the board, which in this case would be 24V. You can find this information on the wiki page of the board you are using. This is an example: https://onstep.groups.io/g/main/wiki/26597”

, which capitalizes Weirdly & misinterprets words just To keep you on your toes


Mark Christensen
 

Guy,

Measure the coil resistance of the motors and see what you get. The info I could find on the 23 types (not an exact match, though) is that the resistance ranges from  2 to 3.3 ohms. 0.3 (cited elsewhere) is awfully low.
Another parameter that is often ignored is inductance: High inductance motors cannot slew as fast. Ask Faraday or Henry.

If you have to get different motors that is not a big expense as long as changing the mechanical interface isn't too hard.

If there is a 12V regulator on the motor side (as opposed to the control, but that should be 5 or 3.3V anyway) it will stop you from being able to drive the motors with higher voltage. You should ask Ken why he jumpered it before undoing it.

If all else fails you might make an adapter so you can put a calibrated load on the worm and see just how much torque that Ealing mount needs. It is probably much higher than what most amateur mounts require. You might find you need to go to motors with a planetary gearbox to increase torque and then use a coarser step size.

I agree with you on using external aircraft style connectors. I even use an external USB bulkhead connector so I can reprogram without pulling the board out of the scope housing. Plus by using external case connectors you are not putting mechanical strain on the PCB.

Yes, working in the cold is no fun. I just finished hypertuning a friends stock CGEM-DX but I can't call the job done until I test it and (probably) make some mechanical tweaks. It has been -3 to 10 above here at night lately and my old body can't take it as much as it used to. In the 1970s I visited a friend at U of Michigan's observatory at Peach Mt, MI. It got down to 26 below zero F. The discrete transistor counters on the photometer locked up, as did the dome motors. We had to climb up and crank the shutter closed by hand.

Have fun!

Regards,
Mark Christensen


Ken Hunter
 

Guy, etc...

2 points to make...

1. The steppers on the bench... If they will not run at Guide or Slewing speeds on the bench
then they will surely NOT be able to drive the Telescope mount out there in the cold.

2. Guy said the mount was balanced... I am having horrible dreams thinking that the mount
counterweight is hanging down with the Dec Axis pointed straight up with no scope attached.
Please tell me this is not the case and how the mount balance was obtained.

If the scope Axis (RA AND Dec) is not precisely balanced it will be very difficult for the stepper
motors to overcome the imbalanced condition. Even changing from a 1-1/4 eyepiece to a 2"
eyepiece can cause enough of a balance problem to make movement difficult depending on
how far the eyepiece is from the Axis.

Guy... If you have any docs on the mount maintenance or especially the method for balancing
the mount, please send me a copy or link to it.

I am willing to chat with you guys all day if necessary to walk you through setting and checking
the mount balance but... Only if the mount has ALL scopes and instruments installed as if you
were going to do an actual observing session AND you have a few others there with you so they
can help and also learn the process.

A Penny can lift a 10 pound weight ! Ask me to prove it.


Guy Brandenburg
 

Hi, Ken,

Right now, we have taken absolutely everything off of the mount, except for some bolts: all four OTAs, all of the finders, all of the counterweights, the large steel plate all of that was bolted to, and even the cover for the Ealing counterweight box.

When the mount was last operational, we balanced everything on both axes and in all positions by adding or subtracting counterweights of various sizes and compositions, in various locations, and also by sliding some of them along special grooved racks we fabricated. And loosening and sliding and reclamping the OTAs as needed. If we attached any imaging gear, we re-balanced. (Or at least I did. I hope other users did so as well.)

Right now, during very preliminary trials, it’s not balanced at all in RA because the empty CW box sits on one side. The DEC axis is balanced because the six remaining bolts are evenly spaced. My next stop will be to fabricate and rig up an counterweight of some sort to balance out the empty Ealing counterweight box. Maybe this weekend. I wish it were not 50 miles away.

In raising a big weight with a penny, it’s like Archimedes supposedly said: all you need is a long enough (weightless) lever, or (I would add) the proper gear set, and almost no friction….

Sent from my iPhone, which capitalizes Weirdly & misinterprets words just To keep you on your toes


Robert Benward
 

Guy,
If you double the voltage, the current will rise to twice the value in a given time.  If you terminate the pulse at a certain current, you will reach that time twice as fast (which means more RPM).  The higher the voltage, the better the performance at high RPMs & torques.  The voltage does makes a significant difference. Use 24V.  In your case, you might even go higher.  You most likely do not need that regulator near the motor connectors.  Unless you are using drivers that can't handle the voltage, just jump out the regulator pin1 to pin3.

While playing with slewing, a few things can happen, you are going too fast for the motor, you are not allowing the current to rise high enough before you terminate the cycle. 

You can also stall the motor (which you did with your fingers), the motor loses step, and you are finished. 

The motor needs a ramp up time, it can't go from zero to 500RPM in an instant, you need to ramp it up slowly.  Once you skip a step, the motor will most likely stall and you need to go to zero again and start over.  So, for starters, keep you slew rate in check, start slow.  In config.h, this is listed as acceleration time.

Missing the target current can cause a fault, a possible cause while ramping up and then stalling (I think you are using TMC5160).  Setting a target current too high will cause this.  Start low in both current and slew rate, and go back and forth between the current and the slew speed increasing each a little at a time.  Eventually you will reach the maximum RPM you are going to get out of the combination of motor and voltage. 

Look at the curves at the bottom, the faster you go, the less torque you can deliver.  At speed, you may only have 10-20% of the holding torque.  The bottom graph shows the starting RPM for a given torque and no load torque, and the then the maximum torque at speed.

Bob



Once you are through the time constant, the current is simply V/R (note, you may never get there at high RPMs).


Speed Torque Characteristics PKE Series
Stepper Motors Speed Torque Curve


Robert Benward
 

Guy,
I found the stepper motor part number you are using on a Brazilian website.  See the text highlighted in red:
Maybe this is why they stall so easily?
Bob
Description

Nema23 4Kgf Stepper Motor
BRAND : MOONS
MODEL : 23HS2427=01 REV C
TYPE BIPOLAR 4 WIRE
DRIVER COMPATIBLE WITH TB6560 , A4988 , DRV5528
WINDING RESISTANCE 0.3 OHM

BEST COST BENEFIT FOR A NEMA 23
GREAT FOR ROBOTIC DESIGN, LOW COST

NOT INDICATED FOR HOME CNC MACHINES, THEY HAVE VERY LOW TORQUE AND THE INDICATION OF THESE MOTORS IS FOR SOME UNIVERSITY PROJECT THAT YOU HAVE TO SHOW THE ROBOTIC MOVEMENT WITHOUT WORRYING ABOUT TORQUE

PLEASE DO NOT BUY IF THE INTENTION IS TO ASSEMBLE A ROUTER MACHINE ETC


Prasad
 

Ken

Guy is 100% on the mark. I was there when Guy removed all the balancing weights on the RA axis. The DEC axis has no load at all. In this condition, I have tried to turn the worm that drives the RA axis by hand. It was very free in both directions (remember 1:359 ratio) but it did get a bit tight at certain positions. This was due to mechanical binding between the worm and worm wheel. Then we loosened the fasteners that hold the worm shaft and the movement became really free in both directions when turned by hand.  (But created some backlash which did not matter for testing the motor). It was very cold that day and we were late. So we wrapped up without completing the adjustment. 

So, as long as the worm shaft is loose in its engagement with its mating worm wheel (gear) it should be OK. The penny is all that is needed at the moment. Of course, adding a good cold temp lube would help additionally, maybe half a penny would work. Guy has made progress since then because he has coupled the second stage worm shaft in its place during his recent visit.

Guy, I hope I am right in my understanding/interpretation. Please correct as necessary. Thanks

-Prasad 



On Friday, January 14, 2022, 11:20:01 AM EST, Guy Brandenburg via groups.io <gfbrandenburg@...> wrote:


Hi, Ken,

Right now, we have taken absolutely everything off of the mount, except for some bolts: all four OTAs, all of the finders, all of the counterweights, the large steel plate all of that was bolted to, and even the cover for the Ealing counterweight box.

When the mount was last operational, we balanced everything on both axes and in all positions by adding or subtracting counterweights of various sizes and compositions, in various locations, and also by sliding some of them along special grooved racks we fabricated. And loosening and sliding and reclamping the OTAs as needed. If we attached any imaging gear, we re-balanced. (Or at least I did. I hope other users did so as well.)

Right now, during very preliminary trials, it’s not balanced at all in RA because the empty CW box sits on one side. The DEC axis is balanced because the six remaining bolts are evenly spaced. My next stop will be to fabricate and rig up an counterweight of some sort to balance out the empty Ealing counterweight box.  Maybe this weekend. I wish it were not 50 miles away.

In raising a big weight with a penny, it’s like Archimedes supposedly said: all you need is a long enough (weightless) lever, or (I would add) the proper gear set, and almost no friction….

, which capitalizes Weirdly & misinterprets words just To keep you on your toes






Ken Hunter
 

I am in communication with someone that has first-hand experience with Ealing mounts.

His comments are that the mount could be ridden by someone and still be able to slew.
Guy has stated that the mount NEVER was able to slew and that it was PUSH-TO only.
There appears to be a difference in what the facts are so I am hoping to find some way 
to get down to the basic situation. I'm told that the Ealing mount has a "Clutch knob" at
the SOUTH end of the RA Axis but NO Movable weights on that AXIS. ROUGH Balance
was the best you could do by installing or removing heavy weights inside the Dec Counter
Weight casting. Supposedly the rough balance was good enough since the Drive apparently
had plenty of torque to move mountains. He mentioned something I had forgotten and 
that some steppers need a small weight added to the shaft (flywheel) to keep kinetic
energy up to the point where the flywheel can help the motor avoid resonance and 
stalling. 

We are going to get this working eventually. My suggestion at this time would be to investigate 
adding a small flywheel to the motor shaft, extending the ramp time and since you have a 24V
power source, give that a try but the motor current is defined by the drivers so I would not
expect that the increased voltage would have as much effect as a flywheel on the stepper
shaft. I would also disconnect the RA Drive by releasing the clutch to verify the motor can at
least drive the gearing up to the big worm gear on the RA axis.


John Petterson
 

Guy,

I found a web page with several of those steppers pictured on it.  If that is a data, it has to be in the format YY/MM/DD as one of the pictured motors has a date of 10/12/28 and another one is 13/09/11.  So yours is probably 7 years old.

John


Ken Hunter
 

Guy...

Do a Google search on Vexta Clean Damper for information on how the "flywheel"
actually works. DO NOT get isolation dampers that mount the stepper on rubber
gaskets. You need the shaft mounted Dampers. There are many listed on eBay
but here is one from the Oriental website for use on a 1/4 inch motor shaft:
https://catalog.orientalmotor.com/item/all-categories-components/ac-motor-accessories/d6cl-6-3f

Same thing on eBay
tinyurl.com/6w7vm6dc

And a video:
https://www.youtube.com/watch?v=S3m5fEwg9K4

Notice the Torque on this motor:
tinyurl.com/3rsdb8wy


George Cushing
 

Don't forget, a stepper is not a DC motor, it is an AC motor. At full steps the driver delivers 2 pulses that are 90° out of phase. These pulses approximate square waves with minimum pulse width under 1 µs. As micro stepping is used the pulses start to approximate stepped sine waves with the current rising and falling with the steps. Allegro's A4988 datasheet is worthy of study to get an understanding of the workings of a driver.


Robert Benward
 
Edited

but the motor current is defined by the drivers so I would not
expect that the increased voltage would have as much effect as a flywheel on the stepper
shaft.
Ken,
It is an inductor, increase the voltage and you increase the RATE OF RISE of the current, enabling faster step rates.  I provided simulation of that below.

Bob

EDIT:  To clarify, yes, the driver controls to a specified current, and in standstill it's simply V/R, but it will be PWM'd to maintain that current (24V/3ohms =8A, we PWM to lower it to 1000mA or so).  What the voltage does is allow you to reach that target current faster, and thus move to the next step faster.   Look at the sim below.  The frequency is ramped from 50Hz to 2000Hz.  Since the current does not rise fast enough before the end of the cycle, it terminates sooner and the current goes down.  This is partly why the torques starts to drop at higher RPMs.  Go look at any motor torque data, it should show one or more applied voltages. the higher the voltage, the higher the torque at high RPMs.  Look below at the sim.  The blue line is the applied voltage.  Near the end it drops from 24V to 12V.  Notice the current waveform below it. See how it drops nearly in half?

Bob


Guy Brandenburg
 

Hi, Ken,
Ealing telescope mounts are built in a very unusual configuration. If you search for “Ealing” on my blog, guysmathastro.com, I’ve got a picture of a beautifully-restored one with a pristine paint job that belongs to a group way out West somewhere.

Ours is not so pretty!

As you mentioned, Ken, part of the balancing is done by putting weights into, or removing them from, a counterweight box. They are really a very strange ‘keystone’ shape with tabs cut out for bolts at the corners of the box, and room for finger holds.

We still have the originals but we also cut a bunch more, in lots of different denominations. With those alone, we are able to get a pretty decent balance in RA.

Bill Rohrer cut the new ones from a slab of steel with a plasma cutter.

We can fine tune it some more by putting other small items in the box if needed.

In DEC, I think the original Ealing’s had a rod you could slide weights along.

Ours has been modified a lot over the past 30 years, by me and by several others — the late Bob McCracken and Bob Bolster, and Bill Rohrer and Alan Tarica Michael Chesnes, to name a few. Aided by all the other members of The Hopewell Corporation that owns and operates the observatory on a figurative shoestring.

This photo shows part of the setup we had, not too many months before the drive died. Compare this photo with one from an original Ealing and you will see a lot of differences along with a lot of identical features.

At the top of the photo, under the two blue handles, is a thick steel slab by Bill Rohrer and held in place by a thick z-shaped channel I fabricated. It’s adjustable, but this photo doesn’t show you how.
Below the Dec axis, it looks like those z-channels continue, but they don’t. (Think about it.)
If you need weight on the opposite side of the Dec axis, you can either simply remove the counter weight slab you see on in the photo, or you can do that **and** slide it onto the other side of the axis. To balance towards the left or the right, we unclamp, slide, and reclamp the various OTAs, such as The blue handles on the Meade 10” SCT hidden behind the big black slab.
The white slab on the left is a permanent counterweight.

These telescopes were only ever slewed with human arm power. The only thing that the tiny little motors did in RA and DEC was drive it smoothly in RA and perform very slow movements and adjustments in guiding and precise aiming.

What we are attempting is some orders of magnitude more motor-powered movement than has ever occurred with this mount.

Tim X of the MIT observatory told me they did a conversion of their old Ealing drive to a SciTech drive. Not cheap! Not DIY! And if you do that you are dependent on one fellow— Dan Gray.
MIT soon put the whole scope into mothballs anyway and bought a much nicer scope and mount (i don’t recall what).
Their budget is a whole lot more than ours!!
So I figured that the original, famous, high-quality Ed Byers gears must be strong enough to power this as a goto




Sent from my iPhone, which capitalizes Weirdly & misinterprets words just To keep you on your toes


Robert Benward
 

Sorry, the picture did not come through.

Bob


Guy Brandenburg
 

In any case, until we get the electrical supply fixed for our 45-year-old roll-off roof, then we can't really put the telescope mount and all the rest to the test. Because you can't aim or slew the scope with the roof closed!

With many thanks to you, Ken, and many other friendly folks on this list, I now think that the board that you made for us will most likely work just fine, with a little bit more fine-tuning of voltages, currents, speeds, pulleys, belt-tensioning, and other parameters in the CONFIG file. And adjust and re-lubricate all the gears so that they mesh properly. I'm going to replace the pulleys I machined (but not well enough) with factory-made ones. And fabricate permanent, but modular, connections from the main body of the scope (where the RA drive lives) up towards the DEC drive cavity, and for an antenna, and the Smart Hand Controller, and mains power.

We are hiring electricians to rebuild the connections and the power supply to our 1947 bomb hoist cable drive for our ROR. (Almost everything else in this entire place was built by observatory members.)

Once the roof and drive are both working, some of us will have to mount the big steel, newly-painted mounting plate and all of its the z-channels and mounting brackets, and then re-attach all of the OTAs.

And re-balance - very important.

Then practice slewing and such, and fine-tune the various CONFIG settings.

That idea of using flywheels is interesting!

I started looking at steppers with higher torque. I never knew they had such a wide range of torques. I should have paid more attention, but everything about this project has been new territory for me! (I'm not griping! It's been fun learning all this!  And I continue to make stupid idiot rookie mistakes!) 

Fortunately, most steppers are fairly inexpensive, and if the ones we have turn out to be weaker than we like, it will be simple to remove them and replace them with ones with more torque -- one only needs to remove 6 machine screws for each axis, and all of those are quite easy to reach.

Again, semi-final fine tuning will need to wait a bit, but we are close. Thanks again for all your help.

The photo of the naked mount illustrates how the RA portion of the counterweight system works with Ealings.


Guy Brandenburg, Washington, DC  http://gfbrandenburg.wordpress.com/ http://guysmathastro.wordpress.com/
============================


On Saturday, January 15, 2022, 11:40:28 AM EST, Guy Brandenburg <gfbrandenburg@...> wrote:


Hi, Ken,
Ealing telescope mounts are built in a very unusual configuration. If you search for “Ealing” on my blog, guysmathastro.com, I’ve got a picture of a beautifully-restored one with a pristine paint job that belongs to a group way out West somewhere.

Ours is not so pretty!

As you mentioned, Ken, part of the balancing is done by putting weights into, or removing them from, a counterweight box. They are really a very strange ‘keystone’ shape with tabs cut out for bolts at the corners of the box, and room for finger holds.

We still have the originals but Bill Rohrer also cut a bunch more with a plasma cutter. So we have a lot of different thickness and weights. With those alone, we are able to get a pretty decent balance in RA, and you can add odd heavy items to fine tune the balance some more.

In DEC, I think the original Ealing’s had a rod you could slide weights along. 

Ours has been modified a lot over the past 30 years, by me and by several others — the late Bob McCracken and Bob Bolster, and Bill Rohrer and Alan Tarica Michael Chesnes, to name a few. Aided by all the other members of The Hopewell Corporation that owns and operates the observatory on a figurative shoestring.

This photo shows part of the setup we had, not too many months before the drive died. Compare this photo with one from an original Ealing and you will see a lot of differences along with a lot of identical features.

At the top of the photo, under the two blue handles, is a thick steel slab by Bill Rohrer and held in place by a thick z-shaped channel I fabricated. It’s adjustable, but this photo doesn’t show you how.
Below the Dec axis, it looks like those z-channels continue, but they don’t. (Think about it.)
If you need weight on the opposite side of the Dec axis, you can either simply remove the counter weight slab you see on in the photo, or you can do that **and** slide it onto the other side of the axis. To balance towards the left or the right, we unclamp, slide, and reclamp the various OTAs, such as The blue handles on the Meade 10” SCT hidden behind the big black slab.
The white slab on the left is a permanent counterweight.

These telescopes were only ever slewed with human arm power. The only thing that the tiny little motors did in RA and DEC was drive it smoothly in RA and perform very slow movements and adjustments in guiding and precise aiming.

What we are attempting is some orders of magnitude more motor-powered movement than has ever occurred with this mount.

Tim X of the  MIT observatory told me they did a conversion of their old Ealing drive to a SciTech drive maybe 8 years ago. Not cheap! Not DIY (unless you have an engineering degree)! And if you do that conversion, you are dependent on one fellow— Dan Gray.

MIT soon put the whole scope into mothballs anyway and bought a much nicer scope and mount (i don’t recall what).
Their budget is a whole lot more than ours!!

So I figured that the original, famous, high-quality Ed Byers gears must be strong enough to power this as a goto




, which capitalizes Weirdly & misinterprets words just To keep you on your toes


George Cushing
 

-14 here this morning. Sue says it's 84°F at her rocker in the south parlor window. Solar tempered indeed.

Torque and current go hand in hand as do stator length. Commonly available NEMA 23s run from 1-4A and 41 to 112mm long.  Holding torque for a typical 41mm 1.5A 23 would be 6Kg/cm and detent torque 300g/cm. As the torque available at low speeds equals the holding torque minus two times the detent torque this motor will make about 5.4Kg/cm. A 112mm long 4A NEMA 23 could produce 28Kg/cm. A 0.3A NEMA 23 sounds like a special order. Probably maxes out at 1-2Kg/cm.

Your typical NEMA 17 will give you 5Kg/cm. It's only when you need more than 6Kg/cm that you should be shopping NEMA 23s and bigger amps.


Khalid Baheyeldin
 

On Sat, Jan 15, 2022 at 10:05 AM, George Cushing wrote:
Don't forget, a stepper is not a DC motor, it is an AC motor. At full steps the driver delivers 2 pulses that are 90° out of phase. These pulses approximate square waves with minimum pulse width under 1 µs. As micro stepping is used the pulses start to approximate stepped sine waves with the current rising and falling with the steps. Allegro's A4988 datasheet is worthy of study to get an understanding of the workings of a driver.
And this short video which Alain Zwingelstein pointed out to me

https://www.youtube.com/watch?v=Ew6eVGnj7r0


Ken Hunter
 

Having photos of the Mount definitely help us see your problem. I take back my
recommendation of a NEMA 17 motor LOL...

Even better than the photo of the naked mount, Here is further info on the Ealing
mount provided by Jay Leblanc who worked on those mounts during the last Century.

If you do determine that you need additional motor torque, I found a motor that you might 
find useful. It has plenty of torque but specifies a MAX current of 2.8 amps. That might
not  be a problem if you slew the steppers at the recommended 50-60% of max.
Otherwise an additional more powerful driver can be adapted fairly easily.

If the end result of all the testing means a bigger motor is needed, then that will have to
 be the final answer to the problem. 
https://www.ebay.com/p/8012054997?iid=333413959686

And one with even more torque but definitely needing a additional power driver.
https://www.ebay.com/p/19043692285?iid=233568963590

And with a driver...
https://www.ebay.com/itm/233498590203?hash=item365d99bbfb:g:a6kAAOSwlHJeS12y

At Kitt Peak in the 70's I helped design and build drives with Differential gears and 
 
 
 

Synchronous motors but they didn't have clutches like your Ealing mount. Instead there
were magnetic brakes on the Axes that were not moving. Still a pain in the ASS.

Steppers were in the works but there were no discrete drivers available so we were
burning the candles at both ends trying to get the ramps under control with discrete
transistors and 7400 digital logic at the time. Many memories of those days keep
flooding back as we work on the Ealing you have.

Hang in there...

Ken