Microscope focus - step motor magnetic coupling

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Pau
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Microscope focus - step motor magnetic coupling

Post by Pau »

This was previously discussed at http://www.photomacrography.net/forum/v ... p?p=229466

Now I've the system working nicely. The original Wemacro coupler does its work but I much prefer my design: much easier to couple and center and more easily switchable between microscopes, it also is capable of sliding without forcing the mechanics but strong enough to do not slide during stacking.

I use Neodymium magnets: be aware that they are very strong but very fragile, I've already broke two of them during their manipulation.

The parts: 20mm diameter custom made aluminum coupler (I am not sure if placing strong magnets too close of the motor could affect its function) with a 20mm/5mm Neodymium ring magnet (very strong!) epoxied. A second magnet ring is just held by their attraction.

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With the Zeiss WL and Standard 18 I use 20mm/2mm round magnets epoxied to the fine focus knob, this is very convenient: self centering and easy to dismount just sliding.
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With the Olympus BHMJ focus block I don't want to use discs because they would prevent the access to the axis screw bolt necessary to dismount the mechanics. Unfortunately I've not found adequate Neodymium rings so I use iron washers, they are less convenient because they are not self centering so I put a plastic part from a door hinge to prevent lateral sliding and decentering. It also works very well.

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The complete system: I've modified a bit the MicroMate with a wider knob and washers and with parts of a door hinge to hold a 2Kg diving lead to improve stability

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Comments and questions welcome
Pau

dolmadis
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Post by dolmadis »

Thanks for posting this Pau.

So this protects both the motor and the focus block if it hits the end of travel?

BR

John

Pau
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Post by Pau »

Yes, it does
I tested several magnets and washer combos with four different microscope blocks during two weeks and this is the best working combo, although most of them were useful.
A magnet disc against an iron washer tends to laterally slip too much while a disc against another disc is self centering.
If you want to replicate my design I recommend to buy an excess of magnets to perform your own tests and to have spare ones
Pau

JH
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Post by JH »

Nice! Thanks for posting. I like it a lot. I hope a lot of people are inspired by this and starts to use a stepper motor. The use of a weight is clever, makes it possible to place the motor anywhere on a table.

One idea for those that wants to build a coupler of their own:
I have found it usefull to have a flexible material somewere between the motor and the fine focusing knob - It takes care of the little missalignement that might be left. As I only use one microscope I do not need to move my motor. Therefore I do not need a strong permanent (epoxi) connection between the washer and the fine focus. Instead I use double sided tape with foam. I have to replace it once in a while but it is easy. One layer of the tape is also enough to handle the missalignement.
Best regards
Jörgen Hellberg
Jörgen Hellberg, my webbsite www.hellberg.photo

dolmadis
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Post by dolmadis »

Are the magnets self centering when two different diameter magnets are brought together please?

Thanks


John

Pau
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Post by Pau »

JH wrote: One idea for those that wants to build a coupler of their own:
I have found it usefull to have a flexible material somewere between the motor and the fine focusing knob - It takes care of the little missalignement that might be left.
Thanks Jörgen,
The aluminum shaft coupler closer to the motor provides some flexibility. Unfortunately mine seems defective, it is not perfectly straight when not forced so I prefer to put the custom cylinder shaft very deep to limit its flexibility, I'm waiting for a replacement unit.
In fact I did my tests with double sided tape and only epoxied it when I was sure to have the right combination.
Pau

Pau
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Post by Pau »

dolmadis wrote:Are the magnets self centering when two different diameter magnets are brought together please?
John, I can't do more tests as most of my magnets are of 20mm diameter, I only can say with a 18mm over a 20mm disc or over a 20mm ring.
In both cases centering is pretty good but not as exact as 20 over 20, they allow some decentering, no more than 1.5mm anyway. Over a bigger ferrite disc they are not auto centreing at all.
Pau

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