DIY Automated rotary table for automatic polar measurements - diyAudio
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Old 11th April 2012, 06:44 PM   #1
_Wim_ is offline _Wim_  Belgium
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Default DIY Automated rotary table for automatic polar measurements

Design goals:
- make a complete polar measurement with 1 mouse click
- table must be strong enough to carry my Abbey clone speakers (+-50kg)
- it must be DIY

Status so far:

- PIC motor en encoder control board finished
- rotary table finished
- positioning works very accurate and fast (PID controlled)
- "scope" function for position routine works also (used to fine tune PID parameters)

What's left:
- program shortcut key's to make it easier to control it from Auto-It script
- adapt Auto-it screen to work with new software and ARTA
- do some code clean-up
- writing some documentation
- testing testing testing...


I will make all source code open source, and executables will also be posted. The pcb is very simple (see circuit attached). The only "difficult" thing for DIYers will be programming the PIC and finding a suitable motor cheaply.

I found a PITMANN motor on Ebay with a reduction of 63 and a 256 inc encoder for 30 . Maxon motors with quadrature encoder show also up every now and then. For bearing I used one of these: Drehkranz Drehlager Drehteller Drehscheibe 330 mm | eBay

remark: I have no affiliation with this seller. I just posted this because its ideal to make an automated rotary table.

The above should allow many people here to build an automated rotary table.
Attached Images
File Type: jpg USB_WIM_IO.JPG (285.7 KB, 318 views)
File Type: png main screen.png (24.7 KB, 316 views)
File Type: png parameter finetuning.png (54.6 KB, 309 views)
File Type: png parameter setup.png (12.5 KB, 302 views)
File Type: jpg IMG_4804.jpg (94.4 KB, 303 views)
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Old 11th April 2012, 06:52 PM   #2
_Wim_ is offline _Wim_  Belgium
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Question by Gedlee posted in another thread:

Would you sell me one? What kinds of loads will it take? That usually ends up being the problem.

One suggestion. I do not test at equal intervals, its better to have more forward resolution than aft. But typing in the numbers would also be a pain. Could a numerical table be setup where one just clicks a button and it goes to the next value in the table? That coupled with HolmImpulse would be exceptional.

I may even make my polar mapping program available and for the first time in history we could all be looking at very high resolution and accurate polar data that is done the same way and hence comparable.

------------------------------------------

I will not be selling anything. But as everything will be made open source, it should be easy to build one. I also have no problem at all with somebody else making kits available. I would even encourage this, but I do not have the time to do this myself.

Loads: the brearing I use can take 300kg (theoretically). For testing I place my desk chair on top of it while programming (that a load of +80kg :-) )

Nummerical table: this should be possible. I still have some work with the Auto-It scrip but I will look into that.

Coupled with HolmImpulse: that should be no problem to write a script in Auto-it to do this. Currently I am targetting ARTA because it has a polar responce plot and holm does not.

Integrating your polar program: I am very interested to take a look at this. In what language is it written? I currently use C# 4.0 in VS2010.
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Old 11th April 2012, 06:57 PM   #3
ra7 is offline ra7  United States
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This is freakin' awesome! Thanks!
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Old 11th April 2012, 07:05 PM   #4
_Wim_ is offline _Wim_  Belgium
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Thanks!

It is based on the excellent Auto-It script of
Fabian Reimann (see http://www.artalabs.hr/AppNotes/AP-8...%20EngRev1.pdf) and on the excellent PIC USB framework of Simon Inns ( see Open Source Framework for USB Generic HID devices based on the PIC18F and Windows - WFFwiki)

Without there work I would not have been able to do this, so you really should thank these guys!

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Old 11th April 2012, 07:29 PM   #5
_Wim_ is offline _Wim_  Belgium
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TIP: if you look on the German Ebay site for "Drehkranz Drehlager", there are apperantly multiple sellers who sell these kind of bearings.
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Old 11th April 2012, 08:32 PM   #6
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Wow very cool. I've been thinking about something like this for a very long time, although I wouldn't make it automated. The problem I keep running into is how do you keep the baffle equidistant from the microphone? As it spins, doesn't the driver/baffle move further from the measurement point?

I've been trying to figure out a track method to put the mic and stand on a track that circles the speaker. I've stated building the stand. 2" PVC pipe set in a 5 gal bucket of concrete. Then an arm sticking out that houses the mic.
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Old 11th April 2012, 08:38 PM   #7
gedlee is offline gedlee  United States
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Quote:
Originally Posted by _Wim_ View Post
Integrating your polar program: I am very interested to take a look at this. In what language is it written? I currently use C# 4.0 in VS2010.
I use VB.net in VS2010 - not identical but extremely similar. The number crunching is all done in FORTRAN because of the superiority of this languages numerical abilities, but this is just linked in as a DLL - there is no user interface to anything FORTRAN.

My techniques are extremely complicated, but they yield extremely high resolution data. Far better than anything that I have seen from ARTA or any other program. There is more to doing an accurate polar map than just plotting the raw numbers.
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Old 12th April 2012, 05:44 PM   #8
_Wim_ is offline _Wim_  Belgium
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Quote:
Originally Posted by gedlee View Post
I use VB.net in VS2010 - not identical but extremely similar. The number crunching is all done in FORTRAN because of the superiority of this languages numerical abilities, but this is just linked in as a DLL - there is no user interface to anything FORTRAN.

My techniques are extremely complicated, but they yield extremely high resolution data. Far better than anything that I have seen from ARTA or any other program. There is more to doing an accurate polar map than just plotting the raw numbers.
Sound very interesting. I have programmed VB.net before (actually learned VB.net and then switched to C# for a customer), so that is not a problem.

It would also be very interesting to compare the diffences between an ARTA polar and a Gedlee polar. Please send me your code, and I look into it. If it works ok, I think it would be possible for me to program 2 buttons: "automated measurement with ARTA" and "automated measurement with HolmImpulse".

I am currently looking into the possibility to control ARTA/HolmImpulse from .net by using one of the following:

UI Automation Overview

white

This way I could avoid using an external AutoIt script, which is much more flexible.

I will be travelling for the next couple of days, so probably will have no time to post here.
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Old 12th April 2012, 07:11 PM   #9
gedlee is offline gedlee  United States
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I am not sure that I want to let the code out of my hands. I am not a hobbiest, I do this stuff for a living and its very valuable to me. Best case I would make the executable available, but right now its still a little buggy. I can always get it to work, but its not always obvious what the problem is. As you know there are lots of ways that a program can crash.

I would love to do an ARTA comparison because everything that I see from ARTA looks far better than what I get with my system - by that I mean that ARTA is not showing the "warts" that I see. Might make sales better I suppose!

How about you do a measurement of a system with ARTA and send me that data (impulse responses) and I'll plot it on my system then we will post the two results. (I am sure that the impulse responses measured from ARTA are fine as long as they use log swept sine as in Holm. Its the post processing of these impulses that is the tricky part.) As I have posted before, I use 0, 5, 10, 15, 20, 30, 40, 50, 60, 80, 100, 120, 150, 180 degress. This is almost ideal if you look at where the maximum rate of change with angle is and put more points at higher rates. I can deal with equal spacing, its just more points, but nothing over 7.5 degrees in the forward direction is worth doing as there is not enough resolution in the data to get good results. Every 5 degress works well, but its far more data than is really required. Every 10 degrees is too coarse.

Can we do that?

Last edited by gedlee; 12th April 2012 at 07:14 PM.
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Old 12th April 2012, 08:02 PM   #10
_Wim_ is offline _Wim_  Belgium
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Sound ok for me. An exe or DLL could work also, if it comes with some documentation.

I first made the ARTA part work, and we will see from there...
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