OpenServo Version 3

Discussions relating to development and use of the OpenServo hardware.

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BasicFox
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Post by BasicFox » Thu Sep 17, 2009 10:31 pm

kbb wrote:
BasicFox wrote:http://be.farnell.com/texas-instruments ... /1621010RL
would this do the trick?
As MOSFETs Q1 and Q4 for the OpenServo V3? If, so, then a definite no...

You're looking for this:

http://be.farnell.com/international-rec ... dp/1374975

i.e. IRF7307TRPBF
but that is an other package, i already have the propeller head design pcb here at home, the parts i search are reffered as U5 and U6 here his schematic: http://homepage.mac.com/cliff_huston/.p ... OSXv3a.pdf

kbb
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Post by kbb » Thu Sep 17, 2009 11:29 pm

BasicFox wrote:
kbb wrote:
BasicFox wrote:http://be.farnell.com/texas-instruments ... /1621010RL
would this do the trick?
As MOSFETs Q1 and Q4 for the OpenServo V3? If, so, then a definite no...

You're looking for this:

http://be.farnell.com/international-rec ... dp/1374975

i.e. IRF7307TRPBF
but that is an other package, i already have the propeller head design pcb here at home, the parts i search are reffered as U5 and U6 here his schematic: http://homepage.mac.com/cliff_huston/.p ... OSXv3a.pdf
Sorry, I misunderstood.

The IC you've linked to (SN74LVC1G126FCKR) is not a replacement for the SN74CBT1G125DCKR. Two problems: the meaning of output-enable is inverted and it's not a FET bus switch.

You can find the datasheet for the SN74CBT1G125DCKR at

http://focus.ti.com/lit/ds/symlink/sn74cbt1g125.pdf

I have not been able to find an equivalent on the Farnell site, so far. Do you use any other suppliers? Such as "Digikey"? If you use Digikey, then here is the link to it:

http://search.digikey.com/scripts/DkSea ... -6410-1-ND

Kevin.

BasicFox
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Post by BasicFox » Fri Sep 18, 2009 8:05 am

but these parts are for the Back EMF function i think they are not really needed in the schematic while the OSv3 software doesn't support it,
i assambled an order at digikey and the 20MHz resonators are out of stock there :p

kbb
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Post by kbb » Fri Sep 18, 2009 5:12 pm

BasicFox wrote:but these parts are for the Back EMF function i think they are not really needed in the schematic while the OSv3 software doesn't support it,
i assambled an order at digikey and the 20MHz resonators are out of stock there :p
Yes, as far as I can see it will be okay to drop U5 and U6 from the build if you’re not going to use the back EMF facility. In which case you can leave C10 off as well. Even R11, R12, R17 and R18 would then appear to be redundant!

The only minor condition is that we will need to check that the software sets an appropriate state for pins PD7 and PD4 on the controller, if necessary. Which is not a problem.

Kevin.

BasicFox
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Post by BasicFox » Mon Sep 21, 2009 10:34 am

could not sample from texas instruments but i have found an other manufacturer that has an identical part: Pericom with the PI5C3301, i have placed an sample order of that IC, i think with that i can make the BEMF working too :D

Cliff
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Post by Cliff » Mon Sep 21, 2009 1:37 pm

BasicFox,

The TI SN74CBT1G125 was chosen because it has built-in clamp diodes on the I/O pins and as long as a negative spike causes less than 50mA to flow (constrained in this case by the divider resistors), the part will not be damaged when an I/O pin goes below ground. When the motor is shutoff to sample BEMF, the voltage on the bus switch input will spike below ground. See this post for a better explanation: http://www.openservo.com/forums/viewtop ... =2073#2073

The Pericom part does not appear to have the clamp diodes and may be damaged when used for the OS3 BEMF circuit.

Cliff

jharvey
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Post by jharvey » Sat Oct 17, 2009 3:19 pm

I made my first OSV3 last weekend. Took me a bit to catch up enough to be able to post, about it. Any how here are some notes.

I used a toaster re-flow toaster oven I made, and a solder mask from http://www.pololu.com/catalog/product/446

I first populated parts for the AVR side, then re-flowed. Then I flipped it, and populated parts for the other side. Then suspended it on a wire rack, such that it was supported by two horizontal wires with the AVR facing straight down in the re-flow oven. The components on the AVR side stayed in place while the components on the other side re-flowed. I know the bottom side re-flowed, because I was a bit hasty when taking it out. I didn't give it much of a cool down period before I grabbed it off the rack. When I did, I bumped some of the components on the rack, and moved them off their mark a bit. Next time I'll be slightly more patient, and that should prevent some rework.

jharvey
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Post by jharvey » Sun Oct 25, 2009 10:36 am

I'm looking for a connector that I can use to program my OSV3's for the first time. I found this picture, and I know the connector isn't perfect, but it's not far from what I'm looking for.

http://www.openservo.com/moin.cgi/ServoBootstrapping

Anyone know what the part number of that connector is?

ginge
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Post by ginge » Sun Oct 25, 2009 12:32 pm

That one is actually an old ISA card slot which has been cut down to size.

At the time that adapter was made, we couldn't source a 2x4 ISA style slot, so I am not sure if you are going to be able to get one easily.

Why not add the hirose connector and then build a flash cable?

jharvey
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Post by jharvey » Sun Oct 25, 2009 1:24 pm

My plan is to solder my wires directly to the board, decreasing cost and eliminating some assembly time. Also if you program and verify that it works before you solder on the connector, you might save the connector. Basically I see connectors as a source of problems, and I'm planning to remove them if I can. The DF11 connector is certainly a great connector, and well suited for this application. I just don't want them if I don't need them. Also by soldering directly to the OSV3, I don't have to modify the case as much. Just those little nibbles near the motor.

The HRS DF11 connector is 2mm center to center, I'm having trouble finding an edge connector with 2mm centers. I do see a pile of 1mm center, perhaps one of those with every other lead removed. Perhaps this one, cut down to a 10 pin connector.

http://datasheet.octopart.com/1612163-1 ... 520460.pdf

BasicFox
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Post by BasicFox » Sun Oct 25, 2009 4:14 pm

jharvey wrote:I made my first OSV3 last weekend. Took me a bit to catch up enough to be able to post, about it. Any how here are some notes.

I used a toaster re-flow toaster oven I made, and a solder mask from http://www.pololu.com/catalog/product/446

I first populated parts for the AVR side, then re-flowed. Then I flipped it, and populated parts for the other side. Then suspended it on a wire rack, such that it was supported by two horizontal wires with the AVR facing straight down in the re-flow oven. The components on the AVR side stayed in place while the components on the other side re-flowed. I know the bottom side re-flowed, because I was a bit hasty when taking it out. I didn't give it much of a cool down period before I grabbed it off the rack. When I did, I bumped some of the components on the rack, and moved them off their mark a bit. Next time I'll be slightly more patient, and that should prevent some rework.
lol this might sound very stupid but the last day's i tried to solder the pieces onto the board, now i see that is impossible, making the OSv2 with a solder iron was possible but the OSv3 is out of my reach :p

the main problem is the microcontroller, all the other parts can be solderd onto the board... tought about placing the pcb on the electric cooking plate and heat it up (with only the avr on it)

what temperature does it has to be to melt the tin? And do u use any other products to melt it better or something?

edit: found this link: http://www.sparkfun.com/commerce/tutori ... ials_id=60 (toaster to reflow oven tutorial) and it seems i also need solder paste

jharvey
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Post by jharvey » Sun Oct 25, 2009 6:14 pm

Solder paste is a good start, I recommend this fellows paste.

http://www.kd5ssj.com/index.php?option= ... &Itemid=54

The 256 is good paste. I've got a tub of it. This fellow bought it and will put a bit of it in a syringe and send it your way for a small fee. A small amount goes a long way. I've also tried other paste's, but be careful. One of the pastes I got was literal a guy with a block of led, a grind wheel, and some plummer flux. That stuff was junk. The fellow from above, also has a recommend low cost soldering technique. I seem to recall it cost around $30 or something like that. Should work for the OSV3. Browse his page, he used to have some videos showing his recommended soldering technique.

I also made a re-flow toaster oven, using this control board.

http://www.thesiliconhorizon.com/cms/in ... &Itemid=57

The techFX 3.0, with a B&D infra-wave is great. Total cost was a bit over $200 usd. The max temperature I used so far for the 256 paste is 220C.

Bummer to hear about the Sparc garbage. Because of what they are doing to SparkFun, I certainly won't recommend them for anything I ever do.

BasicFox
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Post by BasicFox » Thu Nov 05, 2009 5:33 pm

i've orderd the paste when i read your message and now i got a mail that he just received the new load of it and i get two tubes of the price of one (because i had to wait) a good guy!!

jharvey
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Post by jharvey » Thu Nov 05, 2009 9:34 pm

Yeah, Cash Olsen has always been good by my standards. Some times a bit crazy, but aren't we all. I think you'll really like that stuff.

rotdrop
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Do-it-yourself: overall costs?

Post by rotdrop » Tue Dec 15, 2009 11:25 pm

From reading this years posts I somehow have the impression that building your own OSV3 somehow does not pay off (financially), compared to the prices for the pre-assembled versions available from robotfuzz. At least if one does not plan to do similar things very often. So in order to obtain a moderate number of those pieces (say eighteen), and not even counting the many hours of organization and work, would it be worth to try to build those things on your own? Unless, of course, you understand it as kind of setup experience for further projects ;). Do I have the wrong expression?

(off topic: ATM I'm considering to resume my work on a little hexapod hobby project, after letting it pause for a long time. The next stage would be to get rid of the central servo controller and move on to decentralized control circuits, one per leg or so. OpenServo's would be one possibility, using their builtin Mega168 to implement most of the inverse kinematics)

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