OpenServo.com

FireBALL · Joined: 24 Jul 2009 Posts: 28

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

FireBALL · Joined: 24 Jul 2009 Posts: 28

I'm pleased to to report that the board works like a charm and Austrian Micro chips are highly tolerant to misalignment

jharvey · Posted: Sat Sep 19, 2009 1:55 pm Post subject:

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.

jharvey · Posted: Sat Sep 19, 2009 3:06 pm Post subject:

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.

BasicFox · Joined: 15 Mar 2009 Posts: 59 Location: Belgium

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

BasicFox · Joined: 15 Mar 2009 Posts: 59 Location: Belgium

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

jharvey · Posted: Tue Sep 22, 2009 9:29 pm Post subject:

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.

BasicFox · Joined: 15 Mar 2009 Posts: 59 Location: Belgium

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!

jharvey · Posted: Sun Sep 27, 2009 11:04 am Post subject:

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

FireBALL · Joined: 24 Jul 2009 Posts: 28

kewl stuff, keep it coming

BasicFox · Joined: 15 Mar 2009 Posts: 59 Location: Belgium

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.

jharvey · Posted: Mon Oct 12, 2009 10:55 pm Post subject:

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.

BasicFox · Joined: 15 Mar 2009 Posts: 59 Location: Belgium

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 I²C 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

.

ginge · Posted: Tue Oct 13, 2009 9:44 pm Post subject:

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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