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Old 23rd March 2013, 08:01 AM   #1
solhaga is offline solhaga  Sweden
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Default Yet another DIY AMT

After have following båndsei´s thread about DIY AMT, I thought it is best if I start an own thread for the ones I´m making so I don´t clutter his thread with questions on my construction.

So this is a homage to båndsei´s thread, I thank him for all his help (they were others of course) and I hope that my work will be benificial for his in the end.

I´ll start with the motor, this is how it looks in FEMM seen from above:

Click the image to open in full size.

Simulation shows an even field in the gap:

Click the image to open in full size.

The field is 0,325 T in the middle of the curve:
Click the image to open in full size.

The field will be less as the iron actually is a bunch of 3x10 mm rods with 3 mm air in between (the green stuff):

Click the image to open in full size.

Total size of motor is 200 mm wide, 160 mm high and 40 mm thick.

Membrane will be 250 mm wide and 160 mm high folded to fit into a 120 mm wide, 160 mm high and 10 mm deep magnetic gap:
Click the image to open in full size.
There´s a lot of work before this is ready...
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Old 23rd March 2013, 09:58 AM   #2
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Splendid.
How many folds,pleats,are you planning?
Active diaphragm is going to be quite large,and that might be a good idea.
Pleats are then 7-8mm deep?

Good luck.

Båndsei
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Old 23rd March 2013, 11:55 AM   #3
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Quote:
Originally Posted by solhaga View Post
Total size of motor is 200 mm wide, 160 mm high and 40 mm thick.

Membrane will be 250 mm wide and 160 mm high folded to fit into a 120 mm wide, 160 mm high and 10 mm deep magnetic gap:

There´s a lot of work before this is ready...
It will be interesting to follow this project.
I think your calculations are a bit off - you will have 8 to 10 mm between the center of the folds...
The slot loading will then only be approximately gone (no slot loading) and my experience then is that you get a driver that are radiating from a 45 degree angle and without slot loading.
I do not know how this may work in practice, but I see a multitude of issues that will and can give you trouble.

I would have expected the diaphragm width to fill the 120 mm should have been increased from the 250 mm up to somewhere between 500 mm to 2000 mm to achieve slot loading properties.

However the forces may cause the top and bottom of the folds to somehow wobble in and out, and the middle of the pleats will curve in and out. So maybe this will give an interesting kind of "radiator" effect..

Last edited by RayCtech; 23rd March 2013 at 12:07 PM.
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Old 23rd March 2013, 08:11 PM   #4
solhaga is offline solhaga  Sweden
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Join Date: Jun 2009
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First I will build the motor and then the membrane.
I know for sure that there will be many membrane incarnations before I get it right.
The one above will be used as a proof of concept of the way to insert the membrane.
BTW, the motor will be 30 mm thick, not 40 mm.
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Old 24th March 2013, 02:38 PM   #5
solhaga is offline solhaga  Sweden
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Join Date: Jun 2009
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Default Assembling the motor, pt 1.

Got the iron: quality S235 IRG+C, dimnsion 10x3 mm.
It got sharp edges and is highly magnetic. The iron is cut into 200 mm long rods:

Click the image to open in full size. Click the image to open in full size.
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Old 24th March 2013, 02:48 PM   #6
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Dont you need some iron cut at 40mm to place in betvine.

Bernt.
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Old 24th March 2013, 02:51 PM   #7
solhaga is offline solhaga  Sweden
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To get the correct spacing I cut 25 of the rods in half as spacers during glueing.

Click the image to open in full size. Click the image to open in full size. Click the image to open in full size.

Perhaps I can re-use them if I want to do a slimmer design.
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Old 24th March 2013, 02:53 PM   #8
solhaga is offline solhaga  Sweden
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Quote:
Originally Posted by båndsei View Post
Dont you need some iron cut at 40mm to place in betvine.

Bernt.
No, this is the front (or back, it depends what will parts that will look the best).
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Old 24th March 2013, 02:57 PM   #9
solhaga is offline solhaga  Sweden
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Time for some gaffa tape:

Click the image to open in full size.

Adding plastic 3 mm spacers as filler and to stop the glue:

Click the image to open in full size. Click the image to open in full size.
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Old 24th March 2013, 02:59 PM   #10
solhaga is offline solhaga  Sweden
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Before glueing, time for a reality check:

Click the image to open in full size.
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