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MM-11 stepper motor

 
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Charles Krebs



Joined: 01 Aug 2006
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Location: Issaquah, WA USA

PostPosted: Sat Jan 28, 2017 7:03 pm    Post subject: MM-11 stepper motor Reply with quote

I recently put a stepper motor on my MM-11 "hybrid" (see: http://www.photomacrography.net/forum/viewtopic.php?t=17656& ) to automate stacking. Turned out to be pretty simple really. It is always nice for me to see what others have done... gets the brain cells working... so Here are a few details that might come in handy for someone else.

One aspect that was different from many microscopes is that on this one the entire "head" (trinocular head, objectives, camera) move up and down instead of a stage moving up/down. So the motor needed to be attached to this main unit.

This was accomplished by using a 0.19inch thick piece of aluminum plate attached at the bottom as can be seen in the pictures below.



The fine focus knob is a large, nicely machined metal piece on this scope and I did not want to remove it or permanently modify it. Since the Nema 17 motor has a 5mm shaft I wanted to put a 5mm shaft on the knob. I found some hubs and shafts that allowed me to do this (details below). It took two different attempts to attach the hub accurately centered. What worked (the second method) was to remove the head and position it "sideways" on a table in a way that the knob pointed straight up but I could still freely turn the fine focus knob on the opposite side. With the 5mm shaft attached to the hub I put a thin, even layer of JB Weld "KwikWeld" on the bottom of the hub. This is an excellent epoxy adhesive and it gives you about 5 or 6 minutes to slightly adjust the position of the part. By rotating the fine focus rapidly from the opposite side, and observing the shaft end, it was quite easy to "eyeball" the hub and shaft to nearly perfect center. After that it was pretty straightforward to align and couple the two shafts. I had a few different couplers. The first one gave me a "wobble" even though I had carefully aligned the shafts. The second one was a different type and it ran perfectly "true"!



A) Hub with 5mm hole. Pololu item 1203. https://www.pololu.com/category/137/pololu-universal-mounting-hubs

B) 5mm diameter 25mm long shaft. Servocity. https://www.servocity.com/5mm-stainless-steel-precision-shafting

C) 0.19 inch thick aluminum plate.

D) Nema 17 mounting bracket. Pololu #2266. https://www.pololu.com/search?query=nema+17+bracket&x=5&y=8

E) 0.9 degree (400 step per revolution) stepper motor from WeMacro. This is controlled with the WeMacro control box and their Android program on a tablet (blue tooth). http://www.wemacro.com/

The WeMacro software is very simple and there are far fewer optional settings than the Cognysis StackShot controller. My primary initial concern was that you can't customize the units for distances. But it worked out pretty nicely. The WeMacro rail comes with a 200 step motor and the leadscrew is 1mm/full revolution. This Nikon fine focus mechanism is like many other microscope blocks in that you get 200 microns of travel per full turn. So the math works out that with a 400 step motor you need to multiply your desired step size in the control software by "10". (For example, a desired "8" micron step will be entered as "80" in the control program. Very easy to get used to.)

Without micro-stepping it gives 1 micron movement per step. The controller can micro-step and will provide much smaller steps than 1 micron but I won't need them (perhaps rarely) on this scope because of the objectives I typically use with it.
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Beatsy



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PostPosted: Sun Jan 29, 2017 5:01 am    Post subject: Reply with quote

Thanks for this info Charles. Narrows down the options I was considering. Cheers
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johan



Joined: 06 Sep 2011
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PostPosted: Sun Jan 29, 2017 7:14 am    Post subject: Reply with quote

Yeah, me too, thanks Charles. Absolutely delighted to see the WeMacro unit work for you!! I'm not sure if this arrangement will work for me though because I don't have a double movement axis as such, and if I connect the stepper permanently to the fine focus like this it'll stop me being able to fine focus by hand. So I'm thinking something like Rik's hosepipe connector, one that I can slip on and off easily. Labophot-2 has a cover over the fine adjustment that I should be able to use for this. I don't have any machining skills though so the connector to connect the stepper to the scope needs a little thought.
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Pau
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PostPosted: Sun Jan 29, 2017 9:07 am    Post subject: Reply with quote

Charles, clean and nice implementation, thanks for posting it!
Did you be able to buy the Wemacro without rail?
I'm too thinking in a similar implementation, Stackshot is expensive and I'm thinking in Arduino, likely this is an intermediate -price wise- and easier solution

Johan,
Quote:
I'm not sure if this arrangement will work for me ...
...if I connect the stepper permanently to the fine focus like this it'll stop me being able to fine focus by hand

This is also my main fear, but I think that the shown setup also provides the solution: I guess that just unscrewing the locking bolt holding the glued hub (A) and the motor axis (B) will free the fine focus movement, could I be right?
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johan



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PostPosted: Sun Jan 29, 2017 12:08 pm    Post subject: Reply with quote

Pau wrote:
Charles, clean and nice implementation, thanks for posting it!
Did you be able to buy the Wemacro without rail?
I'm too thinking in a similar implementation, Stackshot is expensive and I'm thinking in Arduino, likely this is an intermediate -price wise- and easier solution

Johan,
Quote:
I'm not sure if this arrangement will work for me ...
...if I connect the stepper permanently to the fine focus like this it'll stop me being able to fine focus by hand

This is also my main fear, but I think that the shown setup also provides the solution: I guess that just unscrewing the locking bolt holding the glued hub (A) and the motor axis (B) will free the fine focus movement, could I be right?


Yes, or loosening the coupling that holds the two shafts together? I'm just a little bit unsure of the long-term viability of something that requires me to undo and reset a precise mechanical coupling. I'm sanguine enough to know that if it's a solution that isn't completely idiot-proof, it'll catch me out sooner rather than later. Also, vibrations from the motor. If I could have some sort of join connecting motor and scope which included vibration-eating material as part of that join train that'd give me a tick on a checklist of worst case scenarios.

Right now I'm leaning towards somehow bedding the single spare Stackshot motor that I could buy from Cognisys on a bed of sorbothane, below and parallel to the fine focus control, finding 2 matching cylindrical 'knobs' with tracks/notches/tracking, to put on the fine focus control shaft and the stepper motor shaft, and a chain/connector/drive of some sort that sits exactly and predictably in those tracks. Do bear in mind that microscopes are very much virgin territory for me, so my comments are just guesses as to what's needed!!!
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ChrisR
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PostPosted: Sun Jan 29, 2017 12:40 pm    Post subject: Reply with quote

Magnetic clutch?
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Charles Krebs



Joined: 01 Aug 2006
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PostPosted: Sun Jan 29, 2017 3:18 pm    Post subject: Reply with quote

Here's another approach that I had considered for awhile...

Watch this video:

https://www.youtube.com/watch?v=AhNP50elA50&t=3s

Pay attention to the part that is attached to the "Z" motor (looks like a cross between a cupcake form and a funnel). I spoke with Jim Averill, the creator of this. That piece is 3D printed from a material that has some flexibility and (for want of a better word) some "stickiness". It is pressed onto the fine focus knob when you want to use the motor. Pull it away and you are free to manually use the fine focus.

My tentative plan was to get one of the Pololu hubs listed above. Then find a suitable sized funnel. Cut the spout off the funnel and figure out a way to attach it to the motor hub (Probably that same JB Weld epoxy since it would give you the opportunity to run the motor slowly as it hardens and thus allow you to "center" the funnel). Next I would get some Sugru. Put some release agent on the fine focus knob. Put a blob of the Sugru into the funnel and press it up against the fine focus knob to create a custom fit mold inside the funnel. Let the Sugru harden and then pull it off.

I would then put one of my mini Arca clamps at the bottom of the motor mount. Have it "ride" on an Arca plate. You could then slide it against the fine focus knob when needed or back it off (or remove it completely) when not needed.

Using Sugru as mentioned above would mold a custom fitting to a particular knob. If you has several microscopes with different knobs it should be possible to make a "generic" one that could fit a range of knob sizes. Instead of using Sugru to make a custom "fit", line the funnel with some adhesive backed rubber or perhaps dip it into one of those "liquid rubber" materials.

With the MM-11, the way I have been using it I rarely used the "built-in" Nikon fine focus. I use the Zeiss stage to hold subjects and that has a more convenient fine/coarse focus. The Nikon fine focus on my MM-11 does not have a calibration dial either so I used the Zeiss stage for both fine focus and stacking. So fastening the stepper to the knob was no great loss at all. But with most conventional microscopes I can fully understand the desire to not "cripple" the fine focus with a (semi) permanent attachment to a stepper. I'm pretty confident the method just discussed could work quite nicely.
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enricosavazzi



Joined: 21 Nov 2009
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PostPosted: Thu Feb 02, 2017 1:27 pm    Post subject: Reply with quote

Pau wrote:
...
Quote:
I'm not sure if this arrangement will work for me ...
...if I connect the stepper permanently to the fine focus like this it'll stop me being able to fine focus by hand

This is also my main fear,
...

It does not have to be. In my Arduino system, when not stacking the fine focus motor is under the control of a rotating digitizer that, in essence, transmits the motion of the digitizer to the fine focus and works like one of the ergonomic (and expensive) remote focus controls one sees in high grade research microscopes.
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Pau
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PostPosted: Thu Feb 02, 2017 3:13 pm    Post subject: Reply with quote

So...if the stepper motor is not under current, does it can freely rotate?
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genera



Joined: 05 Oct 2011
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PostPosted: Thu Feb 02, 2017 3:32 pm    Post subject: Reply with quote

Pau wrote:
So...if the stepper motor is not under current, does it can freely rotate?


Yes, but remember that you should never rotate it manually with power applied. You can potentially blow out the driver.

If you try this would you come back and comment on whether or not the motors detents interfere in any way with focusing?
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genera



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PostPosted: Thu Feb 02, 2017 3:43 pm    Post subject: Reply with quote

I'd also like to point out that you can get motors with double shafts. With a knob on the outboard shaft you wouldn't need to reposition the motor assembly if you wanted to focus manually. I guess the down side of that is that it might make it too convenient or too tempting, leading to drive failures because the power wasn't turned off.
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Charles Krebs



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PostPosted: Thu Feb 02, 2017 8:31 pm    Post subject: Reply with quote

Pau wrote:
So...if the stepper motor is not under current, does it can freely rotate?
If there is no power to the motor you can use the fine focus without "de-coupling" the connection at some point. In my case is is not as silky smooth as when no motor is attached, you can feel a slight "bumpy" sensation as the motor shaft turns past "detents", but nothing really bothersome. I don't know how it would be with a 200 step motor, but with the 400 step motor I don't notice any loss in precision positioning. But keep in mind on this scope a 50/0.50 would be the objective needed the most precise positioning... might be an issue with higher NA objectives. (If you are well aligned it probably would not be a big deal to loosen one of the set screws on the coupler.)
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mawyatt



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PostPosted: Fri Feb 03, 2017 11:04 am    Post subject: Reply with quote

What if you just placed a simple switch in line with each motor winding. Example, push the Red button to disengage the stepper windings and allow manual rotation. Release the Red button to re-engage the motor?

Anyway just a thought.

Mike
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