OpenServo.com

Aahz · Joined: 12 Oct 2006 Posts: 12

I just got my OpenServo boards in the mail (thank you RobotJay!) and I realized I have no idea where the connection from the board to the servos are and I can't seem to find it on the website. Can anyone direct me to the propper information?

Aahz.

robotjay · Posted: Fri Feb 02, 2007 6:38 pm Post subject:

Aahz,

There are 2 small holes in the corners farthest from the Pin headers. These are where you solder the leads from the motor inside your servo. I don't think it matters which lead goes to what hole, but maybe I've just gotten lucky. There is a strip of 3 slightly bigger holes just below the MCU. (Assuming that the pin headers are on the bottom.) These holes are for the potentiometer. Again, I don't think It matters too much as long as the middle wire comming from the potentiometer goes into the Middle Hole in the board. Here's a picture of the board and where you should connect things:

[Editors Note: The placement of the motor wires in the diagram below is incorrect. Please see the notes further down in the thread regarding the correct location to attach the motor wires.]

Hope this clears things up for you.

-Jay
_________________
"Nothing is fool-proof; For we fools are ingenious and will find a way."

mpthompson · Joined: 02 Jan 2006 Posts: 650 Location: San Carlos, CA

Aahz, I'll be getting my boards from Jay in the next day or two. I haven't seen the physical boards myself so I don't want to give you the wrong information and have you prematurely burn your boards out. Hopefully Jay, Berry or someone else will chime in soon. If not, I'll let you know as soon as I get my boards.

What I can tell you from my OpenServo design is that on the two IRF7309 MOSFET chips that comprise the H-Bridge, the motor is connected to pads that connected to pins 5, 6, 7 and 8 of each MOSFET.

Also, you will have to get the polarity of the motor matching the polarity of your potentiometer. Basically, if the first time you apply power to your programmed OpenServo and set the PID gains it flies to the extreme ends of the servo, you will either need to swap the +/- pins of your motor or swap the two outside leads of the potentiometer.

Good luck with your boards and we'll do our best to help you get them running well.

-Mike

ginge · Posted: Fri Feb 02, 2007 7:00 pm Post subject:

mpthompson · Joined: 02 Jan 2006 Posts: 650 Location: San Carlos, CA

Ooops. Sorry Barry.... Embarassed

Feel free to mispell Mike whenever you wish. Wink

robotjay · Posted: Fri Feb 02, 2007 7:13 pm Post subject:

Aahz · Joined: 12 Oct 2006 Posts: 12

Cool, thanks guys. As soon as the connector for my Gumstix gets here I'll post my results.

Aahz.

ginge · Posted: Fri Feb 02, 2007 9:33 pm Post subject:

Gumstix eh? I have some Gumstix source for controlling and flashing an OpenServo if you want Smile

Barry
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http://www.robotfuzz.co.uk/

Aahz · Joined: 12 Oct 2006 Posts: 12

Sure but that's a bit down the road for me yet. Just getting the whole thing wired up physically and programticly will take me a good while to begin with.

Aahz.

mpthompson · Joined: 02 Jan 2006 Posts: 650 Location: San Carlos, CA

Jay, I just received your shipment of OpenServo boards. In looking at how to hook them up to my Futaba 3003 hardware I believe there is a mistake in your drawing below where the motor leads should go.

The two pads that you indicate are actually through holes that connect directly to the MCU and should not be connected to the motors. Hopefully I'm not confused myself.

With your current boards the best method of connecting the motor wires are directly to pins 5,6 ,7 and 8 of the FETs as Barry described and is shown below:

After looking at your boards I have a number of suggestions for improvements if you are open some ideas.

-Mike

ginge · Posted: Sun Feb 04, 2007 10:56 pm Post subject:

Mike, your image is exactly how I connect mine.

The boards Jay had made were Stefans derivative of my Eagle interpretation of your board. Phew, that was tough. Basically it's been butchered a bit.

I think we made a few commits to CVS after these were fabricated to sort a few issues out. I am sure there is lots that can be changed. I would like some solder pads for these motor connections for a start. I have also requested that we either clean up the top screen print, or remove it all together. These issues are mainly of my making as Stefan only made a few changes.

maybe we should start a OpenServo V3 hardware thread to fix your issues and also get some of the new hardware related features implemented, as discussed in other threads.

Barry
_________________
http://www.headfuzz.co.uk/
http://www.robotfuzz.co.uk/

mpthompson · Joined: 02 Jan 2006 Posts: 650 Location: San Carlos, CA

Below is a picture of my first servo created from Jay's pre-assembled OpenServo PCB. Having the OpenServo board pre-assembled is SOOOOO NICE!!!! The board seems happy as a clam within the case.

Barry, I agree that we should start on an OpenServo v3.0 design that addresses manufacture and assembly issues. With some minor tweaks we can certainly eliminate some confusion and make the assembly process a little more straight forward.

What is of prime importances is that Jay has a way of getting the boards manufactured at a very reasonable price. We no longer have to go blind soldering surface mount parts.

I hope to have some time this week to put together a photographic tutorial of the steps required to go from an unmodified servo + Jay's pre-assembled PCB to a functioning OpenServo.

-Mike

ginge · Posted: Mon Feb 05, 2007 12:16 am Post subject:

That looks great!

I have some photos of my assembly, but your servo looks a lot nicer than mine Wink

Barry
_________________
http://www.headfuzz.co.uk/
http://www.robotfuzz.co.uk/

robotjay · Posted: Mon Feb 05, 2007 2:47 pm Post subject:

Mike,

On the only successful test of the OpenServo I have made, I used the rows of pins from the FETs as you described. I did this because it was easier than trying to poke the wires through those 2 holes near the top of the board. I assumed though, that those holes were the proper placement of my hook-ups. I must've read the schematic wrong.

In working with the ICS servos from Kondo Robotics, I noticed that thier Potentiometer, Motor, and wire leads all connect to the PCB through solder pads, and not through holes. When we implement the v3.0 of the OpenServo, we should really make the hook-ups for all the components one sided solder pads. It'll make things a lot easier.

As far as my assembly goes, I have enough equipment, that as long as we don't make a whole lot of changes to the components we use, building a new version will not be a problem for me.

Mike, I am VERY open to suggestions for improvement, so please e-mail them to me, and we can see what we'll do about them. Talk to you soon.

-Jay
_________________
"Nothing is fool-proof; For we fools are ingenious and will find a way."

ginge · Posted: Mon Feb 05, 2007 5:34 pm Post subject:

Jay,

I Prefer the through hole option for my servos, as like Mike's servos they have a tough nonflexible metallic strip designed to go through hole. I would also be concerned with any vibration shake the pads off. I have already seen vibration affect the motor terminal connections on one of my servos.
Using through hole gives that little bit more strength and flexibility.

Maybe a compromise between the two with a large pad with a hole?

Barry
_________________
http://www.headfuzz.co.uk/
http://www.robotfuzz.co.uk/