Best available steppers, boards, controllers, etc?


Guy Brandenburg
 

We have a venerable but beefy and smooth university-grade German equatorial mount from the 1970s, whose “dumb” electro mechanical drive has clutches and variable-speed controls that have been an intermittent problem from Day 1. The RA drive is currently on my desk; the old clutch pads had come off. Adjusting the new pads and gears and solenoids is not trivial!

We are therefore looking seriously into converting to an OnStep drive. One major problem: the various boards, controllers, etc recommended on various parts of the OnStep wiki either seem to have compatibility issues or else are not in stock and/or not being produced.


we are neophytes at building anything this complex.

I have the RPM measurements for the various gears. For example, tracking speed on the worm gear that sticks out in that photo is 5 rpm with no load. The synchronous motor that drives all this is rated at 60 rpm with a torque of 1/900 HP. 

So does that mean that the worm gear would need a torque of 12 times 1/900 horsepower? And we could use a belt with two sheaves of equal size, and a geared stepper mostly running at 5 rpm, or a 1:2 pulley ratio with 10 rpm?

what are the current driver and controller and board recommendations for something like this?

thanks so much.

Guy Brandenburg
Hopewell Observatory


Mark Christensen
 

Guy,

The problems people seem to have are with the boards that were originally designed for earlier model numerical control (usually 3D printer) machines, esp. the ones that were designed for earlier stepper driver mini-boards.

With the Mini- and Maxi-PCBs, which were specifically designed for OnStep application none of those problems happen. The best driver to use is the TMC5160 based ones - they work well with the SPI control (no fiddling with setting Vref for current control - it is all done in software) and they have the latest StealthChop modes. And can handle the most current with or without (obviously more with) fins and a cooling fan.

On horsepower, what really matters is torque. But, roughly speaking 1/900th horsepower is about 0.83 watts. Assuming similar performance then a 1/900 horsepower motor running thru a 12:1 gearbox would produce about the same torque as a 10 Watt stepper. Most steppers are more like 12 to 30 watts. That would suggest that almost any decent sized stepper would work. But looking at your picture it sure looks like you have multiple stages of gear reduction with, I would guess, some kind of solenoid that either shifts gear ratios or disengages the motor (the large black item on top). So while at first blush almost any stepper, say, a NEMA 13 or 17 form factor with a max current (ignore the motor voltage if it is less than 12V or so - the drivers are current control devices) under 2 amps the TMC5160 should be fine. The fly in the ointment is if the total reduction gearbox (from motor shaft to worm) is more than the 12 to one you stated.

A lot depends on your goals - if it is to produce a GOTO system then you don't want a ton of gear reduction between the motor output (sans gearbox) and the worm. You didn't say how many teeth are on your worm wheel (the big gear right on the axis)., but if you had something like 360 teeth on the wheel then 200 step motor running at 16 microsteps (3200 total steps per stepper shaft revolution) and a 1:3 total reduction between the output of the stepper shaft (gearbox and pulleys combined) and the worm drive would give you better than 1/2 arc sec resolution and, since the TMC5610s interpolate down to 1/256th of a step, even smoother tracking. If your worm wheel has fewer teeth then you could use a bit more gearbox reduction. If you want the system to be able to do fast slews (as is the case with GOTO systems) you don't want to overdo the gearbox/pulley business. The inductive reactance of the stepper windings reduce the torque if you overdo the step rate. And there is no reason to have excessive gearbox reduction.

Are you the same Guy Brandenburg who used to run telescope (mirror) making classes in the DC area and was active on ATMFREE???

Regards,

Mark Christensen 


Khalid Baheyeldin
 

On Wed, Oct 13, 2021 at 05:12 PM, Mark Christensen wrote:
The problems people seem to have are with the boards that were originally designed for earlier model numerical control (usually 3D printer) machines, esp. the ones that were designed for earlier stepper driver mini-boards.
This assertion is incorrect.

Not all 3D printer or CNC boards are equal.

For example, the MKS Gen-L V2 is underpowered but does an adequate job if all you need is a two motors. It does support the SPI drivers (TMC2130 and TMC5160). It is low cost, so attractive as a proof of concept for some users who want to try out OnStep, before they commit to it.

The CNC V3 is speedy, but by design the ESP32 it uses is pin poor, and compromised must be made for the features that are needed. In addition to that, some minor surgery is needed, and power has to be supplied separately to the board as well as the CNC shield. Wiring for SPI is complicated too. The fact that it is cheap and fast outweigh all this for some users. 

The FYSETC S6 is speedy, and supports the SPI drivers too, and in addition to that, it supports dew heaters and much more. It is what I use, and many others do too.

With the Mini- and Maxi-PCBs, which were specifically designed for OnStep application none of those problems happen.
The Mini and Max are of course capable and speedy, but there are downsides. One has to order the PCB with a minimum quantity of 5 (or is it 10?) and with shipping it is not cheap. Then one has to source all the discrete components themselves, and put them together, which is no small feat for most people. Even if one is capable of soldering, what goes where and orientation needs to be learned, and mistakes happen.

I speak from experience as someone whose electronics knowledge was minimal. It is a steep hill to climb, and lots of time to invest.


Ken Hunter
 

Hello Mark...

I wondered the same thing about Guy... I am the original founder of the ATM_FREE Yahoo Group.
That was so too many years ago. Nice to hear from some of the old timers occasionally.

"Be nice, learn, teach, participate" should sound familiar.

Clear skies.

Ken Hunter
Atm_Ken_Hunter @ yahoo.com
(retired email just like me!)


Ken Hunter
 

GUY...

Contact me OFF Group. gmail kb7hunter

I will donate an OnStep MaxESP3 Controller in a case, a Smart Hand Controller Fully assembled in a case with coiled cord 
ready to drive your scope. Read up on the OnStep operation. You'll  be amazed at what is already programmed into the system.

In a few weeks (fingers crossed) the New (from the ground up) version calledOnStepX will be released. That does not say that there is anything wrong with the old OnStep. Just that it started off small and grew in all directions into a complex, fully capable integrated system. The new version is fully backward compatible and purpose coded in modules that makes Howard Dutton (Owner of the group and OnStep programmer) take a little more pleasure in life. At least that's the plan. This is already done and in field testing now.

I don't need any specific information for building the controller. They are configured with just a few pertinate details like mount type, worm drive gear # of teeth, intermediate gear reduction if any, and number of steps the stepper motor takes to give a full rotation. Most of us use Nema 17, 200 or 400 step/rev motors on RA and DEC and that is quite sufficient for up to a moderate 12 inch well balanced scope. Rule of thumb +++ If you can turn the drive worm wheel using your fingers, the Nema 17 will probably be big enough if tied into a 3 or more : 1 reduction and 144 or more tooth RA gear. If not, OnStep will still work fine, you'll just need to up the steppers to Nema 23 and choose a bit heftier stepper driver. or go for more reduction (higher torque but slower GOTO from a given motor/gear combination).

Listen to Khalid, Drew, Dave and Howard... Read the WIKI and whole whole message data base if you want. It's indexed and searchable for particular interesting subjects, what if's, causes and cures etc. There are a lot of guys that contribute but that is the main cast of characters that you will see here daily. I met you once at Stellafane but doubt you'll remember me. Hell, when I look in the mirror I dont remember me but it's sure good to briing back some of the memories of Mel Bartels and his SCOPE software. Too bad the Parallel Port disappeared... I still have my home made German mount with the home made electronics and no Parallel Port in sight. Sometimes LIFE just SUCKS!

Welcome to OnStep... Hang-on it's a fun ride!

Ken Hunter
Retired founder of ATM_FREE Yahoo Group


Mark Christensen
 

Well, while some 3D/CNC boards can handle all the options, other can't, and Guy's problem was exactly the confusion caused by that situation. As you said, not all boards are equal. So I stand by what I said.
Of course they are not all equal - that is why I referred to 'earlier' boards. And that alone causes confusion to 'outsiders'.

For somebody like Guy who is working with a 'University grade' mounting the difference between a few dollars for a single PCB or $30 for a lot of five to ten boards is irrelevant. I've had to order (not for OnStep) groups of 10 custom boards for $35 to get two, one for prototyping, one for a customer/friend doesn't matter compared to my time.

Yes, some have problems with having to populate boards themselves, but that skill can be found in a lot of places.

Yes, I confess to having much too many decades of working with electronics and PCBs, dating back to vacuum tubes and discrete transistors.

Dealing with configuring the software and mounting/integrating motors is another problem for many.

So Guy has many hills to climb. But it is doable if we give him some hints and point him to the type of (local to him) people who can help.

Regards,

Mark Christensen


Ken Hunter
 

Well said Mark...

I am currently working on an idea that has been approved by Howard (within limits).

The idea is to provide a Wiki page where someone with a desired skillset can "Advertise"
their availability to assist others when they desire to do so. I imagine a Wiki page, similar
to a Cork Board in a restaurant waiting area where you can POST your "Business Card"
and initiate an OFF GROUP connection point. The sticky point is that OnStep is really
an "OPEN SOURCE PROJECT" where "Advertisements" are not usually welcomed.

I am pretty "old school" when it comes to building things. I keep up with the times when 
I can but I'm too old to invest in a 3D printer setup. A lot of the OnStep and telescope
projects offer 3D solutions but my search for someone to make cases for a re-designed
Smart Hand Controller got me no where. I find that a decent case, 3D made can take
most of a day to produce. The results can be not very "pretty" if something goes wrong
in the printing process so it's not something I want to invest my money or remaining time
into doing.

I'm going to open the Wiki page as soon as I can sort out the details of how the
"Business cards" can get posted and what they can contain. It's still a "work in progress"
but the ideas are forming some structure and hopefully Howard and the Developement
Group will approve once I get a workable plan sorted out.


Ken Hunter
 

Just a thought...

Someone could build up a spreadsheet with possible OnStep options along the top (column headings)
and the various boards along the side. Of course checkmarks on the sheet would give a quick glance
answer if the particular build would answer your  needs.

NO, I am not volunteering myself or anyone else as the "someone". I don't have the knowledge about
the different builds but the spreadsheet could be updated as needed to remain current.


Guy Brandenburg
 

I am indeed the same Guy who has just re-opened the DC-area free Telescope Making, Maintenance and Modification Workshop after 18 months in limbo.

While doing a little research for a talk at Stellafane this summer, I discovered that this workshop has been in continuous operation since 1937 except for 2 shutdowns: World War 2 and COVID; it used to be primarily  a mirror-making workshop ... As far as I can tell it's the only remaining at-least-weekly ATM workshop in the country. Thanks to DC taxpayers for allowing us to use the space rent-free!

Also, thanks so much for all of the advice on this list, and especially for Ken Hunter's exceedingly generous offer. I told him that while the ATM (or TM3W) workshop is part of a non-profit (National Capital Astronomers), the Hopewell Observatory is NOT non-profit (not that we make any profits!) and we should pay something.

I attach a photo of what the gearbox looks like now, with all of the complicated clutch mechanism and the synchronous motor and the solenoid removed. We will not be putting it back! The Dec drive will get the same treatment in the next few days. The stepper motors will be connected to the remaining shaft that you see surrounded by the only remaining spur gear. (Still trying to figure out how to remove that one! Can't find any grub screws; I hope it wasn't just pressed on.!)


Howard Dutton
 

On Wed, Oct 13, 2021 at 03:17 PM, Khalid Baheyeldin wrote:
The Mini and Max are of course capable and speedy, but there are downsides. One has to order the PCB with a minimum quantity of 5 (or is it 10?) and with shipping it is not cheap. Then one has to source all the discrete components themselves, and put them together, which is no small feat for most people. Even if one is capable of soldering, what goes where and orientation needs to be learned, and mistakes happen.
There are downsides to the S6 also:

1. It wasn't designed with our application in mind, so a bigger hassle to really finish it off in a proper enclosure with connectors.
2. The I2C is semi-broken.  Yea, it can be worked around, but still.
3. Harder to flash with firmware.
4. All your eggs in one basket.  If the controller takes an ESD hit or you make an mistake and short/overload something you're in for a hassle and some expense/wait.  With a Teensy or ESP32S based controller it's more likely that you'll be able to fix it quickly with swapping the MCU, or a little soldering.  Same for the through-hole MaxSTM design.


Howard Dutton
 
Edited

On Wed, Oct 13, 2021 at 03:17 PM, Khalid Baheyeldin wrote:
One has to order the PCB with a minimum quantity of 5 (or is it 10?) and with shipping it is not cheap.
Oh BTW, here near Philadelphia PA, USA... Qty 5 x MaxSTM3.6 PCB from EasyEDA costs $11.72 delivered.  That's with the lowest cost (slowest) shipping option EasyEDA has which they estimate at 10 to 20 days.


Howard Dutton
 
Edited

On Wed, Oct 13, 2021 at 03:17 PM, Khalid Baheyeldin wrote:
Then one has to source all the discrete components themselves, and put them together, which is no small feat for most people. Even if one is capable of soldering, what goes where and orientation needs to be learned, and mistakes happen.
In my latest design (which not too many have built yet, but reports so far are positive) I've attempted to address issues like these.

The components are easier to source and a guide for doing so is on the Wiki page.  The assembly instructions go to a much greater depth than prior designs and that includes comments about component orientation at each step polarity matters.

The MaxSTM


John Petterson
 

On Thu, Oct 14, 2021 at 03:23 PM, Ken Hunter wrote:
Too bad the Parallel Port disappeared... I still have my home made German mount with the home made electronics and no Parallel Port in sight. Sometimes LIFE just SUCKS!
Ken,

A quick search of Amazon shows up dozens of USB to parallel port adapters.  Not sure if they would work to connect your mount, but it should be worth a bit of time to find out!

John


Alexander Varakin
 

Guy,

Looking at the old drive, I have a feeling that the options, described so far may not work - the mounts must be a beast and require much bigger motors, e.g. NEMA 23 or 34, and stronger drivers, like TBA6600. 
Can you show a picture of the mount, with something included for scale?
How many teeth are on the worm gear?

Alex


Ken Hunter
 

John, thanks for that but I think the mount mentioned is best left laying in the dust.
Ken


jsalbinson@...
 

Hello Guy,
This sounds similar to what I am hoping to do with a large old telescope here at Keele. I have settled on an FYSETC S6 v2, TB6600 stepper drivers, with some software wedges, but the rest will be stock OnStep, SHC and ethernet/encoders included. In your case I suggest you plunge right in: The Maxpcb3/teensy 3.6 with TMC5160 drivers (as the steppers will be close to the control board - my situation is quite otherwise) will do you fine for 2,3 or 4 steppers. Use nema23 motors with gearboxes as needed - a double stack 23 motor (2-2.5Amp) thru a 47:1 gearbox (OMCstepperonline ?) and a 360:1 worm gear at 1/4 step or thereabouts will be more than enough. (Practical experience - such a motor will drive 1 metric ton at a moment arm of 1 metre, provided it is balanced). For the dec a 90 tooth worm/singlestack nema23/5:1 gearbox and 1/16th stepping will be fine. I'd guess that the mount in question isn't quite as big.
Don't be scared. Jump right in. The wiki here, and the fora are among the best up to date sites for doing such a thing. You will learn a lot and have a great deal of fun doing it!
All the best, James Albinson


George Cushing
 

What you bring up is what I have been trying to address with https://www.stmbluepillkits.com/. I stock parts for many of the current designs. By using Asian suppliers and ordering in in larger quantities I can keep the prices for the parts at a fraction that any individual can obtain. An individual may have to pay $5-10 for a PCB board while I can get the cost/board under $2 with an order of 50. 

I've been selling "kits," essentially all the parts needed to build the controller since 2000 with over 600 out the door. I try to cover my costs, my motivation is to give new life to existing mounts. I've worked on too many commercial systems that cost 5 times that of an OnStep system that were not as reliable or as serviceable. 

I have built maybe 50-75 controllers and offer 2 models assembled and tested.  

I agree with Howard that any of the Max ESP32 or Teensy controllers would give you great functionality. The Minis and the R23/CNC3/Hujer Shield models are intended to either meet the constraints of packaging or economy.

I'd be tempted to go with a NEMA 23 frame motor as the diference in size would not seem to be much of an issue given the scale of your project. Waht's the best motor? From my perspective it's hard to beat those $4 Minebeas I got from MPJA.com. Let me know if there's anything I can do for you.