Started new OnStep hardware design


skyguynca
 

I breadboarded a new design for the OnStep design. It will have all the functions of the MaxSTM but no stepper drivers and using a standard wall 5VDC adapter.

When you start looking at the prices for the 3D printer drivers it becomes apparent (example TMC5160 @ $50 each) that there are alot more options that I am familar with that are indeed cheaper and can do the same if not better.

Standard Stepper drivers and closed loop stepper drivers that i am used to using in building cnc equipment are cheaper, and include microstepping. You actually have more options for price and functionallity there. A big bonus if you have a large telescope or heavy telescope and mount it will allow the OnStep that Howard Dutton designed to continue to be used by the ATM guys at reduced cost compared to the other system out there.

Anyway here are some pics of the simple layout and parts on a breadboard. I will use terminal blocks for stepper driver connections. it works like a charm. Howard has done a great job with OnStep. I just need to modify some more code that allows other stepper drivers and a different or additional way to calculate gear ratio or type of drive with ratio inputs.

Thanks Howard for putting the design out there. My MaxSTM works great.

David Mikesell
San Jose, CA


Khalid Baheyeldin
 

On Fri, Jan 14, 2022 at 05:02 PM, skyguynca wrote:
Standard Stepper drivers and closed loop stepper drivers that i am used to using in building cnc equipment are cheaper, and include microstepping.
Which drivers do you intend to use?
Are they external drivers, e.g. like this one?

They are definitely not cheaper than an LV8729 or a TMC2130.

And you don't need a custom design board to use them. OnStep already supports external drivers.
You can still use a MaxSTM or any other OnStep board: just make an adapter board and route the
STEP, DIR and EN pins to the external driver, and it is done!

No new design needed.


Robert Benward
 

David,
There seems to be a shortage of the TMC5160.  I paid $17 middle of last year for a Bigtreetech TMC5160 V1.2.  I believe they are up to V1.3 now, and I do see them from $30 to $47.  Khalid mentioned external drivers, I bought one of these on Amazon for $10.

Generic Step & Dir controller $10:  
https://www.amazon.com/Twotrees-Stepper-Driver-TB6600-Controller/dp/B07PQ5KNKR?pd_rd_w=BlZwm&pf_rd_p=ee521540-07c2-4687-9605-13c98e32ab2c&pf_rd_r=VWGZ0KXPHFRVY92572PG&pd_rd_r=96a98394-7544-4851-ab01-e5492cd422a2&pd_rd_wg=Ma8mi&pd_rd_i=B07PQ5KNKR&psc=1&ref_=pd_bap_d_rp_1_t

TMC5160 V1.2 Ebay, $58 for two pcs.
https://www.ebay.com/itm/393547723888?hash=item5ba145b470:g:-4YAAOSwucphMQVj

Bob


Khalid Baheyeldin
 

To use an external driver, all you need is to do this in the configuration:

#define AXIS1_DRIVER_MODEL            GENERIC
#define AXIS1_DRIVER_MICROSTEPS    OFF

The microstepping will be in the driver itself, and the calculated steps
per degree should be set in Config.h accordingly.

Then you get a piece of perfboard, with 10 pins on each side, and wire
only the STEP and DIR pin, using screw terminals if you so wish.
These pins go to the driver's PUL and DIR pins.


skyguynca
 

Yes external drivers, no not like the one you linked. That is a servo driver, anything servo either ac or dc servo is a bit more expensive.

LV8729 -  Amazon $7, Ebay $8. Limited to 0.8 amps cont, peak 1.5ams
TMC2130 - Amazon only listing 2208 and Ebay $11 each  Limited to 1.4amps cont, peak 2amps

TB6600 stepper driver Amazon  $11, It will run Nema 17 and 23 Stepper Motors, 9 to 40VDC and 3.5amps cont 4amps Max  Amazon

Here is a stepper driver combo, 4amp driver and nema 17 motor $20 Amazon driver and motor

If you shop around even better deals to be had on ebay or ali express.

I have used steppers both open and closed loop on cnc machines from vertical mills, router tables, lathes and plasma cutters. I can get them within .001 repeatable accuracy. Perfect smooth lines and cuts. Accuracy and smoothness that the telescope mount will need in tracking and goto. Micro steps from 1/4 all the way down to at least 32 is available on most drivers. The ones I have about about $22 apiece and go all the way down to 256 micro steps.

You save time soldering and cost of components with board made for running external drivers. Using my MaxSTM is overkill. Realistically almost half of the board and components are used with just picking up the 3 pins for each driver. I know i will only save about $20 on single electrical components, but as far as drivers and steppers it breaks even.

The biggest saving is in time. Probably at my speed I will save about 4 to 6 hours in setup and soldering time not having to install about half of the sockets, caps, resistors and sockets that are not going to be used by using external steppers.

When I am done with the new board and have one sitting here. I will post real time assembly and list the total cost and BOM for a direct comparison.

David Mikesell
San Jose, CA


Khalid Baheyeldin
 

On Fri, Jan 14, 2022 at 06:10 PM, skyguynca wrote:
You save time soldering and cost of components with board made for running external drivers. Using my MaxSTM is overkill. Realistically almost half of the board and components are used with just picking up the 3 pins for each driver. I know i will only save about $20 on single electrical components, but as far as drivers and steppers it breaks even.

The biggest saving is in time. Probably at my speed I will save about 4 to 6 hours in setup and soldering time not having to install about half of the sockets, caps, resistors and sockets that are not going to be used by using external steppers.
I still don't see why you need a new board at all.
Using external drivers has been a feature of OnStep for quite some time now.

Again, you can do all of what you said with a normal OnStep board.
Just don't buy the LV8729 or TMC5160.
In lieu of them, do the following:

Use a 10+10-pin adapter board which plugs in the socket of axis1 and axis2 drivers.

Don'tsolder any capacitors that are specific to the drivers at all. So you save on the cost of components and time to solder them.

Note that the MaxSTM requires an EEPROM chip, otherwise OnStep will not run at all.


John Petterson
 

One issue I see is that these external drivers do not allow changing the microstep rate dynamically for slewing vs tracking, so your slew rate will be limited.  I looked at them a year ago when I was starting to build my controllers, but decided against them quickly for that reason.  They may handle higher speeds better because of the higher current ratings, but  it is still a risk.

 

For A/P it may not be an issue, but for a visual scope that does not spend hours on one target it could get to be a pain.

John


skyguynca
 

External stepper drivers and paired with the right stepper has such a huge speed range. A good example is a nema 34 motor and driver on my router table. I can run at Cutting speeds as slow as .125 inches per minute just as smoothly and accurately as cutting at 6 inches a minute. That is 48x the speed change, well with in the limits of my steppers and drivers. My gantry weighs 328 lbs, when not cutting I can run it at .065 inches a minute without stalling and max rapid speed of 150 inches a minute, again no stalling.

I really can not see a problem on the driver/stepper end of it running a telescope mount in tracking (which I believe is .04 deg/min) to slewing at 6 to 15 deg/s a minute. 

If there is a problem I believe it would be needing to adjust the coding to allow such speeds and in the physical limitations of the scope and mirror mountings.

David Mikesell 
San Jose, CA


John Petterson
 

On Fri, Jan 14, 2022 at 06:18 PM, skyguynca wrote:
I really can not see a problem on the driver/stepper end of it running a telescope mount in tracking (which I believe is .04 deg/min) to slewing at 6 to 15 deg/s a minute.
This is basically the problem.  At 15 degrees/minute, it will take 12 minutes to move 180 degrees.  Are you ready to wait that long for it to move from the North American nebula to the Orion Nebula?


skyguynca
 

The 6 to 15 deg/minute is only a ruff estimate using nema 17 steppers which are limited by the need for more torque (low rpms and torque small stepper need alot of reduction) to start and the mass of mount and scope. The nema 23 steppers i will be using can turn 2500 rpms at 64 microsteps, with the right ratio I should get slewing rates in excess of 120 deg/min with enty of torque to spare.

David Mikesell
San Jose, CA


John Petterson
 

I get it - you want to use something you are familiar with and comfortable with and you are not afraid of designing a board for this.  It will be interesting to see how that set of parts gets mounted on the telescope mount.

Ali Express has the TMC5160s listed at $30 for 2 of them (link below). 

Let us know how that other combination works for you - it never hurts to have another option.

https://www.aliexpress.com/item/33015451918.html?spm=a2g0o.productlist.0.0.3d575747KS6Av8&algo_pvid=14caac1e-5346-4bdf-a5c5-5443a03c6684&algo_exp_id=14caac1e-5346-4bdf-a5c5-5443a03c6684-9&pdp_ext_f=%7B%22sku_id%22%3A%2267191412082%22%7D&pdp_pi=-1%3B30.24%3B-1%3B-1%40salePrice%3BUSD%3Bsearch-mainSearch

John


George Cushing
 

Well, no one pays $50 for a TMC5130. Last six I bought cost $12.50 a piece. Of course it took so long to get them to me AliExp gave me my money back.


George Cushing
 

And if you need to amplify the signals w/o invertong them, there's the venerable NTE2033A, 1.6 to 50V signal amp. Here made to A4988 carrier size.

nte2033a.jpg


Khalid Baheyeldin
 

On Fri, Jan 14, 2022 at 10:03 PM, John Petterson wrote:

I get it - you want to use something you are familiar with and comfortable with and you are not afraid of designing a board for this.  It will be interesting to see how that set of parts gets mounted on the telescope mount.

Ali Express has the TMC5160s listed at $30 for 2 of them (link below). 

And there is nothing wrong with using external drivers, if that is what he prefers.
If that means he saves $10 (2 X difference between $10 TB6600 and $15 TMC5160), then so be it ...

My main issue with his line of reasoning is that he wants to design a new board to use external drivers.
But external drivers are already supported in existing boards.

He just needs to route the STEP and DIR pins from axis1 and axis2 to his drivers.

No new code needed! The configuration supports them already!

I even added them as in option in the Online Configuration Generator.


John Scherer
 

Maybe he just wants to design a small board and share it with the group, for his own reasons.  I for one welcome this and do this often myself (design boards). My easyeda project directory is littered with boards I’ve designed for various projects. Some I’ve used, others not so much. 


Khalid Baheyeldin
 

On Sun, Jan 16, 2022 at 02:58 AM, John Scherer wrote:
Maybe he just wants to design a small board and share it with the group, for his own reasons.  I for one welcome this and do this often myself (design boards).
There are certainly valid reasons for creating a new board.
For example, to fill a void in the current offerings, correct a shortcoming, or having a smaller footprint, ...etc.
Or just to learn how to do it, and so on ...

What I am puzzled by in this case, is that he thinks the current boards have a restriction (can only use StepStick form factor drivers), and therefore cannot not do what he wants (use external drivers).
And based on those misconceptions, and wants to create a whole new board.

The truth is all boards can use external drivers. It is merely a matter of wiring.

He is also thinking of modifying the code for that, with all the long term maintenance headaches that this entails, while the code already has support for external drivers.

Reinventing the wheel ...


skyguynca
 

ok, now Khalid i never ever said that the boards have a short coming. I don't know why you keep arguing that point.

#2 I never said that you could not use an external driver, in fact I did state that i am currently using my MaxSTM in the capacity to test using external steppers and larger or more powerful steppers.

#3 I never said I HAD to modify the code. I stated I was going to modify the code so that steppers that use a digital input that allows changing microsteps could be used.

Why are you so against me doing a project on my own? You have been going after me since I posted this thread. I have never said anything that you keep claiming.

What I did say was i was doing it for me, and it will keep from buying parts  not needed, and shorten build time plus save a few bucks.

Please just stop. If you are against anyone doing anything on their own, so be it but stop attacking please.

David Mikesell
San Jose, CA


Chris Whitener
 

Khalid, I am sure it is not intended, but even when we technically agree with you, you often attack.
I understand and feel what David is saying here as well.
-Chris Whitener


John Scherer
 

On Sun, Jan 16, 2022 at 06:50 AM, Khalid Baheyeldin wrote:
On Sun, Jan 16, 2022 at 02:58 AM, John Scherer wrote:
Maybe he just wants to design a small board and share it with the group, for his own reasons.  I for one welcome this and do this often myself (design boards).
There are certainly valid reasons for creating a new board.
For example, to fill a void in the current offerings, correct a shortcoming, or having a smaller footprint, ...etc.
Or just to learn how to do it, and so on ...

What I am puzzled by in this case, is that he thinks the current boards have a restriction (can only use StepStick form factor drivers), and therefore cannot not do what he wants (use external drivers).
And based on those misconceptions, and wants to create a whole new board.

The truth is all boards can use external drivers. It is merely a matter of wiring.

He is also thinking of modifying the code for that, with all the long term maintenance headaches that this entails, while the code already has support for external drivers.

Reinventing the wheel ...

Valid reasons for designing a board?  I would think simply the desire to design the board might be reason enough.  If one likes to design wheels, design away.