OpenServo.com

[stefanengelke]

Hi all,

it's pretty a long time ago since I wrote my last post. Moving back to Germany and finishing my thesis was more work then I thought.

But to be busy helps to be patient while waiting for ordered parts So I have ordered everything I need to build my own hardware.
And here it is:


For the PCB I have used Barry's Eagle files as a template. I have rerouted some parts to adapt to the newest version and to meet all design rules of OLIMEX where I have ordered the PCBs. I have choosen a laminate thickness of 0.8 mm (0.031'') so it will better fit inside the servo. A little bit tricky was the minimal hole size of 0.6 mm (24 mils) for the vias which seems for me to be bigger then the vias in Mike's design. OLIMEX furthermore provides a service of free panelization. I send them a Eagle brd with the small version and one with the big version of the OpenServo and a map how they should panalized to fit on one PCB and they did the job and even cut them after production. So after two weeks I got them:


Furthermore I have ordered all the parts at Farnell mainly choosing the parts of Barry's European part list.

The soldering job was easier then I thought. Mike's HowTo on building the OpenServo 1.0 prepared me well for my first try to solder SMD parts:


Unfortunately I did the same mistake with the 33uF tantal and have used to small landing pads in my design. So I have used the same work around Mike did:


Furthermore I have ordered too weak 0.1R resistors with only 0.1W so I had to stack 4 of them, too, to gain at least 0.2 W.

After uploading the Software everything was working at first go! Thanks to all of you!!

Now I have my own OpenServo 2.1 and I can concentrate on the software and automatic control again. I'm reading Zeddicus' document at the moment. Great job, collecting all the theoretic background!

[mpthompson]

Wow, those boards look nice. The solder mask makes the board look a bit more professional as well.

What servo hardware are you going with? Also, what's the value of the capacitor you have across the leads to the motors?

-Mike

[stefanengelke]

Yes the solder mask is realy nice. I had no problems with solder brigdes.

The servo hardware I'm using has no specifications. I have ordered it from www.conrad.com ( Part Nr. 22 51 38 ) for 10 ?. The only description was ""Servomechanics without electronics"" and the brand is Conrad Electronic. But I belive they just assemble parts of other manufacturers. Unfortunately it seems like they have removed the product from product line because I can't find the part nr anymore. It's a pity because it looks realy promising and the motor seems to be realy strong. I hope we can soon compare the different hardware by identifing the parameters of the mathematical model for each servo type.

The capacitor was soldered to the leads of the motor when I received the hardware. It was the only electronic part which came with the servo. If I interpet the
brown - black - orange - black - brown
marks right, it is a 10 nF cap.

[ginge]

Nice! Very jealous now

Just out of interest how much did the boards cost?

Also, It would be great if I could have a copy of your new Eagle routing, it will come in handy.

Cheers,

Barry

[stefanengelke]

Hi Barry,

the costs of one PCB with 9 big and 9 small servo boards are:
$33 for the PCB
+ $5 for non-standard laminate thickness of 0.8 mm (0.031'')
+ $2.60 for two non-standard drill sizes
+ $6 for airmail

So it's $2.60 for one OpenServo board. But for my next order I will panelize more boards on the PCB. The reason why I have panelized only 18 was the maximum number of holes per PCB of 500. If you exceed this limit it will cost $3.30 for each 500 holes more. That's not expensive but I just wanted to test the boards of my first order.

Sure you can have the new Eagle routing. I can check them into the CVS. Should we create a new folder for them or should I update your files?

[stefanengelke]

I have checked in the new Eagle boards into CVS.

[ginge]

Great work. At least now we have another verified branch. (I had mine done in the UK, no soldermask though). Great rates from Olimax though, Shame they are on holiday.

Barry

[mpthompson]

You Europeans and your month long holidays. I'm jealous .

Stefan, I noticed that you decided to only bring the four upper connectors outside the case. I'm considering bringing all eight connectors out so I can re-flash the MCU including the bootloader without cracking open the case. I'm hoping this will save me from having to pull the servo out from the robot if the worse case scenario happens and I have to restore the bootloader on the MCU. Any thoughts?

-Mike

[stefanengelke]

Mike, I have read the thread discussing the connectors some time ago. But how do you solder the two row connector to the pcb? It looks like it fit exact with your laminate thickness so one row contact each side of the board. Unfortunately with my laminate thickness of 0.8 mm (0.031'') there would fit two of the boards between the connetcor rows. I was thinking about bending the pins a little bit together but soldering this way is probably not as robuts.

I will try to bend only the lower row so at least one row is soldered properly.

Stefan

[mpthompson]

Stefan, you are correct that the PCB laminate I get from ExpressPCB is perfect for soldering on the dual row connectors. Once the bootloader is programmed only the upper four connectors are needed so you may just want to go with that as it works best for your board. You'll need to do some disassembly to recover the board if for some reason the bootloader becomes corrupt, but I've only had that happen to me once since I've been working with the OpenServo. I'm still debating myself about whether I'll expose both connector rows external to my servos or not.

I actually would prefer a thinner laminate as the thicker laminate I get from ExpressPCB does interfere with some servo cases. However, to do this I'll need to learn to use Eagle and use a different PCB manufacturer.

-Mike

[jstrout]

[dsandber]

I just started a thread about pooling OpenServo orders for fully assembled PCBs.

I e-mailed Olimex about what they would charge per unit.

http://openservo.com/Forums/viewtopic.php?p=1257#1257

Join the ""I don't want to go blind soldering SMT parts"" revolution!