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OpenServo V4 (was OpenServo V3.x hardware update)
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kbb



Joined: 01 Jun 2007
Posts: 180

PostPosted: Wed Apr 07, 2010 11:28 pm    Post subject: Reply with quote

jharvey wrote:
kbb, a while ago you mentioned you were doing a KICAD schematic capture. I don't see that in the CVS yet, is it there?

At the moment I can’t upload to CVS for some reason (I’ll clean my “copy” and have another go soon, it always manages to “add” it this end, which is a pain). I guess I could email it, or a clean PDF copy, to you if you like. It is sufficiently advanced (in appearance and project workspace) and close enough to what I think it should be that I am laying out and routing a PCB (in PCBnew). That will help catch any “gotchas”, it's quite cramped in places. And I had to make some of the components and modules for Kicad myself. So there are quite a few things that I need to check carefully!
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kbb



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PostPosted: Wed Apr 07, 2010 11:33 pm    Post subject: Reply with quote

ginge wrote:
I can't for the life of me see why kbb can't use the CVS. We will get it fixed, even if I have to do the initial add.Cheers

Nor me, it used to work fine. I will delete eveything my end and start again with a fresh copy (again!), "tomorrow".
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kbb



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PostPosted: Tue Apr 13, 2010 11:15 pm    Post subject: Reply with quote

jharvey wrote:
kbb, a while ago you mentioned you were doing a KICAD schematic capture. I don't see that in the CVS yet, is it there?


I seem to be have my CVS client running again, so it can now be found in

"V4-EDA-preliminary-work"

It is all still a work in progress. I've only included the "blank" PCB board file for the moment (edges marked out, but no module placement) as the one I am routing is very much still a work in progress. And very cramped too!: it is quite likely that some of the "user pads" will have to be dropped. RP1 might have to go too: and pin usage may change if it makes routing stuff easier.

Let me know if you spot any errors.

The TQFP is really just a little too large, so it is the VQFN package...

Currently I think everything is "source-able" as specified in the Kicad
project. But this needs to be rechecked.

Quite a few of the modules have had to be created or modified for the project, so footprints and the like still need a through checking.
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jharvey
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Joined: 15 Mar 2009
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Location: Maine USA

PostPosted: Tue Apr 13, 2010 11:41 pm    Post subject: Reply with quote

It's a nice PDF. I'm curious do you plan to post the KICAD files?

I like the way you used page 1, then broke it into the sub sections. I might encourage more of that, I like how it allows you to reuse parts for other projects and such.

A while back I made a schematic with this modular approach. I like how the top level turns into a kind of high level connection diagram, then the sub schematics can be updated as required. I found it real handy when I had one sub schematic that I needed several times. I used a template file such that I would make my changes on one file, then copy it several times making the real source files. That saved a lot of time.

The KICAD and PDF files for this other project I was dubbing with can be found at this link.

http://freeems.org

Then click the SF download link, then click your way to the newest schematic. It might also be handy to see how I was able to include the custom modules/footprints and symbols. That took a couple tries to figure out how to get them to actually come with the distributed files.

Keep it up, and I look forward to seeing more of the KICAD stuff.
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kbb



Joined: 01 Jun 2007
Posts: 180

PostPosted: Tue Apr 13, 2010 11:45 pm    Post subject: Reply with quote

jharvey wrote:
It's a nice PDF. I'm curious do you plan to post the KICAD files?

They are there! Maybe you took the hourly snap shot? The PDF was the first thing I up loaded... and there was probably a couple of minutes before the rest was uploaded whilst I was testing it had actually worked.
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kbb



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PostPosted: Wed Apr 14, 2010 6:58 am    Post subject: Reply with quote

jharvey wrote:
It's a nice PDF. I'm curious do you plan to post the KICAD files?

Ah, if you are browsing CVS online, you need to look here:

http://www.openservo.com/viewcvs/OpenServo/V4-EDA-preliminary-work/?root=cvs

The other directory, with just a PDF in it is my fault - I thought I had deleted it, but it hadn't stuck Embarassed
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jharvey
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PostPosted: Wed Apr 14, 2010 10:06 am    Post subject: Reply with quote

Awesome, and thanks for point me right. I just got a copy and looked it over. I had a problem with the library files for the schematic. I seem to recall these can be made to work without the need to add the library to your primary library source, basically making the symbols relative vs absolute. I'll see if I can recall how to make that happen, and I'll send you some info about it.



Missing libs include transistor.lib, opto.lib, atxmega32a4.lib, osv4parts.lib. I see atxmega32a4.lib, osv4parts.lib are in the directory, and I'm willing to wager a guess that the other two are downloaded libs.

Do I recognize that license as the MIT license, if so good for you. I like the MIT, I feel it's even more open then the GPL. It's also a heck of a lot easier to understand.

On the board layout, the via's are very large, nearly .125 inch ID. I might recommend using module PINTST. It's ID is .025 inch.

I should figure out how to get a CVS account, such that I can commit changes. I can modify some scripts I made for my last project to help automate the PDF process.

Good job, and keep it up.
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kbb



Joined: 01 Jun 2007
Posts: 180

PostPosted: Wed Apr 14, 2010 4:58 pm    Post subject: Reply with quote

jharvey wrote:
Awesome, and thanks for point me right. I just got a copy and looked it over. I had a problem with the library files for the schematic. I seem to recall these can be made to work without the need to add the library to your primary library source, basically making the symbols relative vs absolute. I'll see if I can recall how to make that happen, and I'll send you some info about it.



Missing libs include transistor.lib, opto.lib, atxmega32a4.lib, osv4parts.lib. I see atxmega32a4.lib, osv4parts.lib are in the directory, and I'm willing to wager a guess that the other two are downloaded libs.

transistor.lib and opto.lib come with kicad: the others should "autoload", but maybe this is a difference between the Windows version (that I am using) and Linux version you appear to be using? Are you using a recent version?

jharvey wrote:
Do I recognize that license as the MIT license, if so good for you. I like the MIT, I feel it's even more open then the GPL. It's also a heck of a lot easier to understand.


I have copied the MIT licence that OpenServo has, I prefer it: although I think I saw that some coders have lately added GPL in some parts, which may be an issue (the two are not compatible).

jharvey wrote:
On the board layout, the via's are very large, nearly .125 inch ID. I might recommend using module PINTST. It's ID is .025 inch.


That's not the board layout!: it is just the board edges and whatever Kicad does when you open it and it loads the net list into an empty board. The "vias" are most likely the holes for the pot and motor connections and it has probably assigned the default sizes. Of course, if it didn’t load the libraries, it may be a bit confused about some of the other “pads” as well. Also see the note.

As mentioned in the post above the board is still far from finished, but if I get a chance I will upload it as it stands tonight - with big caveat attached. BTW: I am working in "mm".

jharvey wrote:
I can modify some scripts I made for my last project to help automate the PDF process.


It's only a few clicks for me: “print and convert to PDF”.
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ginge
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PostPosted: Wed Apr 14, 2010 5:49 pm    Post subject: Reply with quote

kbb wrote:

I have copied the MIT licence that OpenServo has, I prefer it: although I think I saw that some coders have lately added GPL in some parts, which may be an issue (the two are not compatible).

I have noticed this also, so at some point I will be reviewing this. V4 will be 100% audited for licensing and cross license problems.

Additionally, we seem to be creeping into the territory of using avrlibc code. This shouldn't be a problem, but I will have to carefully read the licenses on each included file.

If you spot any license incompatibilities (within a single application), please drop me a pm so I can add it to the list.

Cheers.
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kbb



Joined: 01 Jun 2007
Posts: 180

PostPosted: Wed Apr 14, 2010 6:36 pm    Post subject: Reply with quote

jharvey wrote:
On the board layout, the via's are very large...


As promised I have uploaded the actual board layout as far as it has got. Note that this is definitely a “Work In Progress” that is in a state of flux... I have added a comment to it so that anyone who comes across it will be aware of that. I have a feeling I should start from the beginning again... but we will see how it goes during the remainder of the week!

You may need the modules and libraries properly loaded if you want to fiddle with it (depending on what you do). When you first open it, if everything is working correctly it should look something like the image below (click on the image for a bigger version, and then on that for the full size one):

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jharvey
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PostPosted: Thu Apr 15, 2010 12:46 am    Post subject: Reply with quote

kbb wrote:
I have copied the MIT license that OpenServo has, I prefer it: although I think I saw that some coders have lately added GPL in some parts, which may be an issue (the two are not compatible).

Oops, that's my fault. I think you reference the code for OE. That code was part of a project that had GPL for other components, so the GPL was there simply because of GPL's viral component. We simply forgot to scrub it from the OE code. What do I need to do to get that as MIT not GPL?
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jharvey
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PostPosted: Thu Apr 15, 2010 12:58 am    Post subject: Reply with quote

kbb wrote:
transistor.lib and opto.lib come with kicad: the others should "autoload", but maybe this is a difference between the Windows version (that I am using) and Linux version you appear to be using? Are you using a recent version?

from "yum list installed | grep kicad" I get this.

kicad.i386 2007.07.09-4.fc10 installed

I don't know how to get the version out of KICAD so I don't know what version it is. I suspect it is a bit old. Perhaps a year or two. I'm currently downloading then installing the latest non CVS version for windows. I'll run it that way to help minimize problems.
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kbb



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PostPosted: Thu Apr 15, 2010 7:00 am    Post subject: Reply with quote

jharvey wrote:
...
I don't know how to get the version out of KICAD so I don't know what version it is. I suspect it is a bit old. Perhaps a year or two. I'm currently downloading then installing the latest non CVS version for windows. I'll run it that way to help minimize problems.


On my copy it shows the revision in the title bar of “KiCad” and also under “Help->About” of all applications: I am using the latest version: 20100406 SVN-R2508. It can be downloaded from here:

http://iut-tice.ujf-grenoble.fr/cao/

The KiCad home page is here:

http://iut-tice.ujf-grenoble.fr/kicad/

Given the age of the version you are using, any missing features or other issues are more likely due to that than a Windows/Linux difference.
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robotjay
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PostPosted: Wed Apr 21, 2010 5:57 am    Post subject: Reply with quote

Wow. I stopped following the thread for a couple months, and it just took me the better part of an evening to catch back up. Smile

I love the switch to the XMega. Sure, it means I'll have to buy a $200 dev board, but 12-bit ADC has my mouth watering...

I've banged my head against a wall over the connector for the last 3 years, without much luck. The one thing I have come up with is using both a captured lead with a locking connector AND a single row socket. This would completely negate the need to buy (or make) separate cables, as each OpenServo would be shipped with all the necessary cables built in. Then the servo can be plugged into either the host, or the next OpenServo in the chain. I suppose this arrangement doesn't affect the design much. It's more of a manufacturing issue, but it's worth mentioning somewhere. If you would rather have each chain have it's own custom cabling, that's up to you.

Have we considered using a full h-bridge chip like the MC33926 from Freescale? This chip is 5A capable, and would reduce our part count considerably. I don't know how big it is compared to our board, but I know Mike Thompson used it in MG995's back when he was working with Runbot. It's definitely worth looking at, considering how much it could simplify our board.

-Jay
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kbb



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PostPosted: Thu Apr 22, 2010 1:24 am    Post subject: Reply with quote

robotjay wrote:
Have we considered using a full h-bridge chip like the MC33926 from Freescale? This chip is 5A capable, and would reduce our part count considerably. I don't know how big it is compared to our board, but I know Mike Thompson used it in MG995's back when he was working with Runbot. It's definitely worth looking at, considering how much it could simplify our board.


I did briefly look at “motor controller ICs”; maybe I should have pursued it a bit more! A change would directly affect the amount of work in what I am doing at the moment (i.e. routing a PCB).

I am happy to get one and try it out; but this probably needs a fair bit of coding by Ginge, myself or another, so there would likely not be an instant answer. On the face of it it looks like a very plausible solution. But there may be some considerations; so firstly here were my observations (then questions):

I found very few that were suitable for OpenServo; in fact I suspect a handful of freescale devices was pretty much it: MC33887 and MC33926.

Physical size

The majority of the ones I found, at the target power ranges we’re looking for that initially seemed appropriate were a tad too large physically.

The one you have referenced is actually only 8mm by 8mm according to the documentation, so it would be fine, especially as it replaces a lot of other components.

Mounting Cliff style heat sinks would be impractical (only the PQFN package would fit the OpenServo PCB).

It would be less east to implement a "bus bar" (must remember to try and take care of that if we go with this).

There might be more choice if we limited orientation of the OpenServo inside a standard servo case...

Power

The max amps is lower than is achievable with the SO(P)8 power MOSFETs, given the devices that appear to be available. See power discussions elsewhere for notes on what OpenServo might be able to support.

MC33926’s max continuous current is 5A if sufficiently heat-sinked. The apparent need to heat sink them to get near their maximum power has tended to put me off. An actual trial should help determine if this is likely to be an issue. None of the freescale devices that would suit OpenServo go over 5A, and I think they’re probably not “stackable”?

Drop in replacements

Two issues arose: the number of drop-in replacements for these seems essentially non-existent (as opposed to replacing the SO(P)8 packaged power MOSFETs which is relatively straightforward as there is such a large choice). OpenServo would probably be locked to the very small number of freescale devices.

The second issue was the desire from some to use the OpenServo as a “brain” for more powerful off-board MOSFETs; the motor controller chip route seemed less able to support that. However, thinking about it, it would still be possible to dump the motor controller chip in this scenario and use alternative code to achieve that aim: if we are careful to ensure the right connectivity to the MCU is still there.

The charge pump capacitor

The value needed is quite large; even for an “SMD” aluminium electrolytic this looks like a bulky, stands tall from the board item (limits orientation to one way up for a sealed standard servo case. Unless we can use a tantalum capacitor instead? Again, this is something that could be determined from a trial.

Other things

RDS(ON) looks to be larger (factor of 10?) than with power MOSFETs.
PWM frequency is lower than is possible with power MOSFETs, but this may not really be an issue.
Turn on/off times are slower than what is achievable from the wide choice of power MOSFETs, again this may not really be an issue.

Questions

Shall we pursue this?
If none of the above observations are seen as a show stopper, should we pursue this in preference to the MOSFET solution (until it is either successful or abandoned)?

I can easily work up a preliminary schematic for this.
I am willing to try one out, choices seem to be limited to the frescale MC33887 or MC33926.
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