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Open-Encoder-MG995
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BasicFox



Joined: 15 Mar 2009
Posts: 59
Location: Belgium

PostPosted: Thu Sep 17, 2009 5:27 pm    Post subject: Reply with quote

jharvey wrote:
BatchPCB is awesome. Just got my first batch of boards. I ordered 12, they gave me 24. Cost me less than $50 for this pile. They are spot on. I can now make a couple open-encoder for real, yeah!
already made a design for the open encoder? there are a lot of unneccesary components in your schematic, all i have is a small condensator an elco and two resistors
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FireBALL



Joined: 24 Jul 2009
Posts: 28

PostPosted: Fri Sep 18, 2009 5:41 pm    Post subject: Reply with quote

super glued it on custom plastic spindle. It seems strong, rest time will tell

depending upon the results I intend to make some custom spindles (brass) to hold 6x2 magnet

here are the pictures of the hand-soldered pcb, now i need to fire it up and test


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FireBALL



Joined: 24 Jul 2009
Posts: 28

PostPosted: Sat Sep 19, 2009 1:16 pm    Post subject: Reply with quote

I'm pleased to to report that the board works like a charm and Austrian Micro chips are highly tolerant to misalignment
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jharvey
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Joined: 15 Mar 2009
Posts: 359
Location: Maine USA

PostPosted: Sat Sep 19, 2009 1:55 pm    Post subject: Reply with quote

Wow I missed the above couple posts. Looks great.

Yes I put in some extras. I included the AN out, then didn't populate it. Allows people to choose an option if so desired.

I also made some progress on getting a nice alignment. I made this shaft.



Then glued the magnet like this.



Works great. Spins freely, and is right against the chip. This make for a very light reading.
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jharvey
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Joined: 15 Mar 2009
Posts: 359
Location: Maine USA

PostPosted: Sat Sep 19, 2009 3:06 pm    Post subject: Reply with quote

And my first reading that tells me how much backlash this servo has.

# python ./test_OE_reading.py
pos = 26:00 status= 100110 mag: 35
pos = 26:00 status= 100110 mag: 35
pos = 26:00 status= 100110 mag: 35
pos = 26:00 status= 100110 mag: 35
pos = 26:00 status= 100110 mag: 35
pos = 26:00 status= 100110 mag: 35
pos = 26:00 status= 100110 mag: 35
pos = 26:00 status= 100110 mag: 35
pos = 26:00 status= 100110 mag: 35
pos = 26:00 status= 100110 mag: 35
# python ./test_OE_reading.py
pos = 26:80 status= 100111 mag: 35
pos = 26:80 status= 100111 mag: 35
pos = 26:80 status= 100111 mag: 35
pos = 26:80 status= 100111 mag: 35
pos = 26:80 status= 100111 mag: 35
pos = 26:80 status= 100111 mag: 35
pos = 26:80 status= 100111 mag: 35
pos = 26:80 status= 100111 mag: 35
pos = 26:80 status= 100111 mag: 35
pos = 26:80 status= 100111 mag: 35
# python ./test_OE_reading.py

That was repeatable. I have a short arm on it, I would press slightly until I hard the servo kind of click. Indicating the gears have all moved in one direction. I took the above reading. Then I pushed the arm slightly in the other direction, indicating the gear backlash was tightened up in the other direction. This gave me the next reading. Now I have a number I can correlate to as the dead band of the servo.


Last edited by jharvey on Mon May 31, 2010 3:37 pm; edited 1 time in total
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BasicFox



Joined: 15 Mar 2009
Posts: 59
Location: Belgium

PostPosted: Mon Sep 21, 2009 10:07 am    Post subject: Reply with quote

nice results, i have made an pcb where the encoder is face down onto the pcb so it reads the servo like in the datasheet, but that did not give a good result... gonna make an other one that works the same like yours and hopefully i will have my first open encoder too :p
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BasicFox



Joined: 15 Mar 2009
Posts: 59
Location: Belgium

PostPosted: Tue Sep 22, 2009 12:45 pm    Post subject: Reply with quote

i've been drawing the potentiometer and have noticed that the distance between the three metal pins are not equal. Having that in the correct way will improve our allignment i think
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jharvey
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Joined: 15 Mar 2009
Posts: 359
Location: Maine USA

PostPosted: Tue Sep 22, 2009 9:29 pm    Post subject: Reply with quote

I made my holes large enough that they don't have a problem. I hold it in place by glue, not the tabs. The tabs will allow for some motion, and there for less than 12 bits, so I glue it to make sure it doesn't move.
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BasicFox



Joined: 15 Mar 2009
Posts: 59
Location: Belgium

PostPosted: Wed Sep 23, 2009 10:01 am    Post subject: Reply with quote

I'm planning to solder the tabs onto the pcb.

Yesterday i dismantled my cnc and found out one of the parts that needs to be mounted wasn't, therefore i had backlash on my X-axes, with that fixed i don't have any backlash anymore on any of my axes Very Happy what will make my pcb's better and faster to make (don't have to zigzag anymore)!

Now i'm waiting for the ultra small mill's i have ordered so i can mill smaler holes and paths (i've ordered one mill of 0.5mm and two of 1mm)

can't wait to see my first reading out of the open encoder!
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jharvey
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Joined: 15 Mar 2009
Posts: 359
Location: Maine USA

PostPosted: Sun Sep 27, 2009 11:04 am    Post subject: Reply with quote

I've updated the encoder MG995 wiki. It now nearly makes sense and shows pictures of the critical steps I did. Just thought I'd post about it here letting folks know it exists.

http://www.openservo.com/ConstructionTutorial_MG995_open-encoder
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FireBALL



Joined: 24 Jul 2009
Posts: 28

PostPosted: Sun Sep 27, 2009 12:09 pm    Post subject: Reply with quote

kewl stuff, keep it coming
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BasicFox



Joined: 15 Mar 2009
Posts: 59
Location: Belgium

PostPosted: Mon Oct 12, 2009 9:17 pm    Post subject: Reply with quote

finally i have my first open encoder finished Very Happy With my cnc working again i was able to make the pcb and it came out quite good Very Happy




Gonna test it out with the osif first.
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jharvey
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Joined: 15 Mar 2009
Posts: 359
Location: Maine USA

PostPosted: Mon Oct 12, 2009 10:55 pm    Post subject: Reply with quote

I see two resistors installed on the OE board. The OSIF has these resistors, and putting driving resistors in both places may bugger it. It will increase the current you have to sink, so it may make it hard for the I2C to pull itself on and off. I don't see any real harm in giving it a try, but it might now work.

Nice work.
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BasicFox



Joined: 15 Mar 2009
Posts: 59
Location: Belgium

PostPosted: Tue Oct 13, 2009 6:31 pm    Post subject: Reply with quote

ah i see, indeed not necessary if you use the OSIF, but if the openservo communicates with the openencoder, this will be on a seperate IC line, or else there will be problems if you link multiple servo's on the same line. And knowing that the openservo doesn't have much left over place maybe the resistors are better on the openencoder pcb.

When the openencoder is fully tested and does its job good, maybe we can make a standard OpenServo pcb with holes for the openencoder and an openencoder pcb. Then i can make all my MG995 servo's openservo's Very Happy and start building a hexapod or something Very Happy.
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ginge
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Joined: 14 Jan 2006
Posts: 1030
Location: Manchester, UK

PostPosted: Tue Oct 13, 2009 9:44 pm    Post subject: Reply with quote

I have been following this quite keenly. Let me say good work to both of you.

As for the I2C reading of the chip... this may be a problem. I got it into my head we would be using the SPI functionality of the chip. This would be easy, we just hook the SPI up to the OpenServo header and off we go (well maybe not quite that easy)
I2C poses a unique problem.... we are already using it. This means we need to consider a bit banged I2C approach, which is slow and eats away what little code space we have.

Let me think about that one.
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