Interchangeability of stepper motors?

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plantfan123
Posts: 27
Joined: Tue Dec 08, 2020 12:39 pm

Interchangeability of stepper motors?

Post by plantfan123 »

Hello. I am trying to make this DIY focus stacking set-up:

https://github.com/Biomaker/Gametophyte ... ySystem.md

It says you need a RS Pro Hybrid Stepper Motor (0.9°, 44 Ncm, 2.8 V, 1.68 A, 4-wire motor):

https://uk.rs-online.com/web/p/dc-motors/5350401/

How interchangeable are stepper motors like this? Really not a big deal but I'm just trying to avoid customs fees, so would one of these work?

https://bc-robotics.com/?s=nema+motor&post_type=product

These links describes the interface with the motor in more detail:

https://github.com/Biomaker/Gametophyte ... omation.md
https://www.youtube.com/watch?v=ZXCXffMVer8

If not, are there specs that I should be looking for when selecting a different stepper motor for this scenario? Or is it best to just stick with the recommended one? Thank you!!

chris_ma
Posts: 570
Joined: Fri Mar 22, 2019 2:23 pm
Location: Germany

Re: Interchangeability of stepper motors?

Post by chris_ma »

hi and welcome,

it depends a bit how much you know about electronics in general, if you have a solid basic understanding it's quite easy to replace one with another, if it's all completely new then it might be best to stick with the exact parts that are recommended so you have less problems trouble shooting issues.

basically speaking all you need to do is to make sure that the size fits, the power requirements are matched, and the wiring is correct.
chris

plantfan123
Posts: 27
Joined: Tue Dec 08, 2020 12:39 pm

Re: Interchangeability of stepper motors?

Post by plantfan123 »

That's what I was thinking. I'll just get the RS motor, thanks a lot!

Chris S.
Site Admin
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Joined: Sun Apr 05, 2009 9:55 pm
Location: Ohio, USA

Re: Interchangeability of stepper motors?

Post by Chris S. »

Plantfan,

The following should be a very close substitute for the stepper motor Jennifer Deegan used in her build that you reference (I believe you are in Canada, and prefer to source parts from there, so this is a Canadian vendor): Stepper Motor NEMA 17 (68 oz.in 400steps/rev, 3V, 1.7A, Bipolar); SKU: 0786; MPN: ROB-10846; BIN: 2-04-02-04-05. This motor is, though, quite a bit less expensive at current prices.

Let’s work through the specifics:

Both motors have 0.9 degrees per step, equaling 400 steps per revolution. Stepper motors come in a wide variety of degrees per step, but 1.8 degrees perhaps the most common in motion control applications such as this. Jennifer chose a motor with twice this level of resolution, to permit finer adjustments of the focus block.

Jen’s motor has 44 Newton-centimeters of holding torque, which converts to about 62 Ounce-force inches. The motor I’ve recommended above has 68 oz.in. This is a trivial difference, and for a microscope focus block, both these motors have much more holding torque than required.

Both motors are bipolar, which is probably the most important criterion of the bunch. Using a bipolar motor will match the Big Easy driver Jen used and the code she wrote. Also, if you ever want to switch from the home-brew Arduino-based controller to an off-the-shelf controller from WeMacro, Cognisys StackShot, MJKZZ, etc., all these controllers will drive a bipolar motor such as this with no more trouble than terminating the motor's wires to match the controller. (The makers of these controllers will even tell you how to do that.)

Jen’s motor is rated for 2.8 volts, 1.68 amps; the motor above for 3V, 1.7A. Again, trivial differences. Plus, stepper motors are tolerant of a wide range of driving parameters. Finally, in Jen’s video, she instructs the builder to adjust the potentiometer on the Big Easy driver to fine-tune the maximum current going to the motor—so you’ll be fiddling with things a bit anyway. (Also—and don’t worry if this doesn’t make sense now--in Jen’s code, the delay settings between pulses to the motor are fairly long, which in my experience makes things like trying different motors and power supplies extra-forgiving.)

The shaft size on both motors is 5mm. I didn't see a parts list where Jen indicated the size or source of her cogs, but the same cog she used on her motor should work on this one.

In Jen’s video, she instructs you to use a multimeter to figure out which wire colors go together. This works fine, but to save you time, according to this motor’s data sheet, the black and green wires are one pair; the red and blue wires are the other pair.

For a cleaner way of mounting the motor than shown in the video, I’d suggest you get a NEMA 17 L-Bracket motor mount. While these are currently sold out with that vendor, they are very widely available. There is one at the vendor you linked to. (Stepper motors’ mounting dimensions are specified in NEMA sizes; the one I’ve recommended is NEMA 17.)

Good luck with the project! If you have additional questions, I’m sure Jennifer will be happy to help you. Or ask us here--you may have noticed that Jennifer credited our forum at the end of her video. Members of our community advised her during her research.

--Chris S.

physicsmajor
Posts: 108
Joined: Sun May 10, 2020 12:56 pm

Re: Interchangeability of stepper motors?

Post by physicsmajor »

The setup described is inexpensive but it may be worth considering something like the stage I posted up a few months ago, which I think is even better value:

https://www.photomacrography.net/forum/ ... 25&t=41955

Cheapest current listing: https://www.ebay.com/itm/Parker-803-928 ... 3978252441

These are available for under $100 shipped and are far more rigid and capable than a hacked-together microscope stand with stepper motor geared to the fine adjust knob. These come with the stepper already mounted via a linear screw, and also have a sub-micron linear encoder mounted to the stage itself so you know exactly where it is (each step is a bit less than 0.5 um). The encoder lets you use closed-loop control. I pair this with an Arduino (monitor the encoder, talk w/RPi) and a Raspberry Pi (runs the show) with a stepper motor driver and an IR LED to trigger the camera. If you want more info or my Arduino sketch/Python code I am happy to share it.

You can run the stepper alone and it's just a mechanically superior version of the described stage. But then any time you want you can "upgrade" to closed-loop control with the encoder hardware, which simply isn't possible with the microscope block.

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Adalbert
Posts: 2425
Joined: Mon Nov 30, 2015 1:09 pm

Re: Interchangeability of stepper motors?

Post by Adalbert »

Hello Plantfan123,
I use the same controller for the different stepp-motors.
https://www.photomacrography.net/forum/ ... hilit=nano
The NEMA motors I use run with 12V without any problem.
But you have to make the difference between 1.8 and 0.9 degrees in the software.
Best,
ADi

mawyatt
Posts: 2497
Joined: Thu Aug 22, 2013 6:54 pm
Location: Clearwater, Florida

Re: Interchangeability of stepper motors?

Post by mawyatt »

One thing not mentioned with interchanging stepper motors is the internal resistance as related to operating current. With a modest amount of current a stepper motor with a higher internal resistance can become quite hot if not operated in a dissipation efficient mode. If the controller utilized allows various motor parameters, speed/velocity profiles, and motor current waveform manipulation and timing, then the motor self generated heat can better be managed.

A very flexible and adaptable controller (like the Trinamic types) will allow a wider selection of motors of various sizes and parameters which can be optimized for the given stage type and application.

Best,
Research is like a treasure hunt, you don't know where to look or what you'll find!
~Mike

jsp
Posts: 461
Joined: Sat Mar 28, 2015 7:21 pm
Location: United Kingdom

Re: Interchangeability of stepper motors?

Post by jsp »

Hello!

I'm just here to wave and say "Hello!"

I built the system being referenced in the opening post, but I did it with massive amounts of help and advice from the lovely folks here on this forum and also from my husband, who is a computer scientist, so I don't necessarily know the answers that you need.

I'm really glad that you have come here to this forum to discuss building something similar (probably even better). I'll look forward to hearing about what you do and will keep dropping in in case I can help in any way.

Good luck!

Jen

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