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OpenServo Version 3
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Cliff



Joined: 23 Jan 2007
Posts: 150
Location: Saratoga, CA

PostPosted: Sat May 02, 2009 4:40 am    Post subject: Reply with quote

Jared,

Without a doubt you should reject the boards from Advanced. I have had a lot boards made over the last 30 years and I have never seen anything so stupid. This goes way beyond incompetent - straight in to the land of truly clueless.

Advanced knows better. If they are going to employ idiots, they should manage them better and take responsibility when they don't.

Call Advanced sales - Beyond any other issues, they did not route the boards to the outline provided in the Gerber files. They approved the Gerbers and accepted the job, it is their responsibility to delivery boards that match the Gerbers - if they don't you have no responsibility to pay.

Cliff
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jharvey
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Joined: 15 Mar 2009
Posts: 362
Location: Maine USA

PostPosted: Sat May 02, 2009 7:25 am    Post subject: Reply with quote

The good news is that the engineering dept has told me I can discard these boards. The bad news is that I'm waiting for a new set of boards.

I'm curious if I should raise objection to a thickness in their plating. I see nearly no plating on 8 of the 16 power silicone pads. That the contacts nearest the center of the board.



Notice how the light from my scanner, put a white line across the bottom edge of the areas with the plating at a normal thickness. However, it didn't for half of the two power chips. Would appear that they didn't run it in the wave solder machine long enough to heat up any places that the copper would dissipate heat.

Also note, they ran a score line around the board, where it should have been routed. Also also note, the via's for breakaway, are only a mild score line, and not the vias called for. That score line is less than .001" deep. Can hardly feel it with a finger nail.

The thin plating is silver colored and not copper colored, so it is plated. However a constant layer of solder with a solder mask would likely produce varying layers of solder. If it hadn't been the power parts, I wouldn't be all that concerned. I'm concerned it could cause a bad connection due to a lack of solder.

Oh also, a beep test confirms the inside layers are good, so that's another place to find joy in this run.
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Cliff



Joined: 23 Jan 2007
Posts: 150
Location: Saratoga, CA

PostPosted: Sat May 02, 2009 12:48 pm    Post subject: Reply with quote

Jared,

Glad to hear that Advanced is making good on your order.

Hard to tell looking at your picture, but I would guess that the pad plating is hot air leveled solder (not really a plating process but still called plating) and it is not unusual for it to be a bit uneven. The bottom line is how well it solders. Since you now have some throw away samples, try soldering some parts to the boards and see how it goes. If you have bad plating, the solder will not 'wet' the pads and flow evenly. My guess is that you will find that they solder ok.

The substandard vias you see near the break tab are called mouse bites and are usually just un-plated holes. Their purpose is to direct the break when you separate the boards from the tree. As long as there are holes, the plating will make no difference and the board will break away cleanly. You may want to remove any plated barrels that end-up on the board side of the break, to keep them from coming loose later inside a servo. A sewing needle or the like works well for removing the barrels.

Cliff
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jharvey
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Joined: 15 Mar 2009
Posts: 362
Location: Maine USA

PostPosted: Sat May 02, 2009 1:29 pm    Post subject: Reply with quote

I thought mouse bits were when you put a half a hole on the edge of the PCB, usually followed by a line holes. In this case, I thought we only had the line of holes for a relief break. The line of holes, are not holes. They are simply small scratches in the surface. Well it's back to the waiting game.
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Cliff



Joined: 23 Jan 2007
Posts: 150
Location: Saratoga, CA

PostPosted: Sat May 02, 2009 1:59 pm    Post subject: Reply with quote

Jared,

When you break the board away, you get that line of half holes on the edge. The holes are needed to weaken the board where you want it to break.

Did you send Advanced the OSXv3a_Pallet_FAB.pdf ? If so, just ask them to confirm that the new boards will match that drawing, which includes a hole chart and symbols. The mouse bite holes are the 175 15mil NPTH holes shown on the chart. Tell Advanced that plating those holes is ok, since non-plated is not a choice on their $66 service, but holes are definitely needed.

Cliff
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jharvey
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Joined: 15 Mar 2009
Posts: 362
Location: Maine USA

PostPosted: Fri May 08, 2009 10:06 am    Post subject: Reply with quote

I got the advanced order today, well yesterday evening. It looks good. They did the rout correctly, and put in the relief vias as the CAM files tell them to do. When then send me the second attempt, they send a package of act II popcorn. I'm guessing that's their attempt at putting in some humor with the second take.

At this point, my biff is that they falsely advertise what 66each will do for you. If I were to do a second batch, they can do it, but it will cost about twice as much. They made good on their product, but caused a bunch of non-required headache along the way. I'll likely look into other vendors on a second run.

I would post a pic of it, but don't really see a point. The tree has been posted before.

My next step is to get the solder mask. I'm also willing to sell these boards is anyone wants bare boards. If you want some, just say so and we'll figure out the details. Until then, I'll keep moving forward on the plan to populate the first set of boards.
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jharvey
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Joined: 15 Mar 2009
Posts: 362
Location: Maine USA

PostPosted: Sun Jul 26, 2009 5:45 pm    Post subject: Reply with quote

I just modified a batch of 6 MG995's. I have some future requests if possible.

It appears I have the boards with larger vias, however even larger vias would be nice. I don't think you can go to big on these. To reuse the POT leads that came with the MG995, I had to remove two strands from the wires. That allowed the wire to physically fit, but getting the solder to flow was a bit interesting. Also pushing the POT vias further apart would have been handy. It's easy for a small strand to make a bridge. Thermal relief on the MOSFET chips would have made it easier to install the motor cap. Or if we are really lucky, perhaps that cap can be SMT and reside right on the board.

I know it's tight, and I'm not sure how feasible the above might be, but would be nice if possible.

I also updated the wiki for the OSV3 modification tutorial, of the MG995. It includes new pictures, and more clarity.

http://www.openservo.com/ConstructionTutorial_MG995
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jharvey
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Joined: 15 Mar 2009
Posts: 362
Location: Maine USA

PostPosted: Mon Jul 27, 2009 9:38 am    Post subject: Reply with quote

Well, I've got the components and I almost have the SMT re-flow toaster oven. All I need now is the solder mask. I just ordered it and thought I'd post the quote number so other's can purchase it if they desire. This mask is for the pallet A1 version with 32 PCB's per board. I got it from

http://www.pololu.com/stencilquote/1J2312

Cost me just under $90 with shipping. I'll be ordering the SMT paste shortly. The paste is a pain because of the required refrigeration. I'm planning on this paste.

http://www.all-spec.com/products/KPJ256.html
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jharvey
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Joined: 15 Mar 2009
Posts: 362
Location: Maine USA

PostPosted: Sat Aug 01, 2009 2:05 am    Post subject: Reply with quote

I just tested my above 6 servos, I had crossed the wires from my expectations, and had to do a pinch of re-work. That's OK it came out better this way. I updated the MG995 wiki.

I updated the two pictures that show the motor cap and wires such that they are no longer crossed. I also added to the testing section, including a picture of the minimum harness.

Also I've got the pictures hosted with photobucket, and have added attachments to the wiki page. The attached pictures are a mirror copy in case photobucket changes over time. I figured why not let photobucket deal with the graphical bandwidth. The pictures are named the same in both locations.
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kbb



Joined: 01 Jun 2007
Posts: 180

PostPosted: Sat Aug 01, 2009 10:30 am    Post subject: Reply with quote

jharvey wrote:
I just tested my above 6 servos, I had crossed the wires from my expectations, and had to do a pinch of re-work. That's OK it came out better this way. I updated the MG995 wiki.

I updated the two pictures that show the motor cap and wires such that they are no longer crossed. I also added to the testing section, including a picture of the minimum harness.

Also I've got the pictures hosted with photobucket, and have added attachments to the wiki page. The attached pictures are a mirror copy in case photobucket changes over time. I figured why not let photobucket deal with the graphical bandwidth. The pictures are named the same in both locations.

Good work.

One tip you could add: if like me you are going to have many servos (12), then it is best to make sure they are all wired the same from the start, i.e. so that "0" (i.e. the lower position) is the same end of the travel on all the servos. Luckily I knew that going in and it isn’t hard to achieve.

Another thing to note is that if you mount the "motor cap" on the OpenServo board as shown there is a risk of shorting against the ends of those SMT devices under its leads- slip something between them to stop that, you never know what might happen with all the vibration. The cap is a bit tight when mounted on the motor but the right size cap or trimming helps with that. Same deal here, make sure the cap leads will not short against the motor casing, although the cases on mine did not appear to be connected to “+” or “-” on the motor.

I added heat sinks to mine, at the moment I am not sure they are really needed. See here for heat sinks:

Adding heat sinks to OpenServo (based on Cliff's suggestions)

Another tip: certain aspects of the MG995 aren't great, make sure the screw that holds the pot in isn't done up too tight, just enough to hold it in place - then use hot glue (not too much) to "secure" the pot in position.

Another tip: Some of the MG995s I used had chaff in the gear chain - checking it whilst you have it apart may be a good idea - you only have to carefully remove the housing and remove chaff with a toothpick. But if you do accidentally knock out the gears, remember to put it all back together again carefully!

Even with the pot "untouched" (still as installed), some of my MG995s can be positioned before and/or after its full range of travel- be careful not to damage the pot if this is the case with yours. Obviously one might be able to adjust for this by physical modifications inside the servo housing.

I think the MG995 has been superseded by the MG996R (which are also on offer at three times the price I paid for my MG995s). The increased cost may make them slightly less competitive with other servos on the market.

Kevin.
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jharvey
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Joined: 15 Mar 2009
Posts: 362
Location: Maine USA

PostPosted: Sat Aug 01, 2009 1:03 pm    Post subject: Reply with quote

kbb wrote:
One tip you could add: if like me you are going to have many servos (12), then it is best to make sure they are all wired the same from the start, i.e. so that "0" (i.e. the lower position) is the same end of the travel on all the servos. Luckily I knew that going in and it isn’t hard to achieve.


My wiki posts are two fold. One is to remind me how I did it this time, such that a second batch would be the same. I agree consistency is a handy key.

kbb wrote:
Another thing to note is that if you mount the "motor cap" on the OpenServo board as shown there is a risk of shorting against the ends of those SMT devices under its leads


I just added that to the wiki.

kbb wrote:
Another tip: certain aspects of the MG995 aren't great, make sure the screw that holds the pot in isn't done up too tight, just enough to hold it in place - then use hot glue (not too much) to "secure" the pot in position.


Just added a note about this as well.

kbb wrote:
Another tip: Some of the MG995s I used had chaff in the gear chain - checking it whilst you have it apart may be a good idea - you only have to carefully remove the housing and remove chaff with a toothpick. But if you do accidentally knock out the gears, remember to put it all back together again carefully!


Thanks for the notes.
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BasicFox



Joined: 15 Mar 2009
Posts: 59
Location: Belgium

PostPosted: Tue Sep 15, 2009 8:32 pm    Post subject: Reply with quote

is there an OpenServo 3 European Parts List? Have to order the parts now (if there isn't one i can create it)
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BasicFox



Joined: 15 Mar 2009
Posts: 59
Location: Belgium

PostPosted: Wed Sep 16, 2009 7:46 pm    Post subject: Reply with quote

i cant find the correct IC, FET Bus Switch, Single on farnell they are not availeble or it is the wrong supplyvoltage, is this part really neccesary?

and also i see that the crimps for the connector are very expensive, €0.175 for one crimp is that possible... such a small piece of iron :p
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BasicFox



Joined: 15 Mar 2009
Posts: 59
Location: Belgium

PostPosted: Thu Sep 17, 2009 2:37 pm    Post subject: Reply with quote

http://be.farnell.com/texas-instruments/sn74lvc1g126dckr/logic-74lvc1g-buffer-driver-sc705/dp/1621010RL
would this do the trick?
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kbb



Joined: 01 Jun 2007
Posts: 180

PostPosted: Thu Sep 17, 2009 10:17 pm    Post subject: Reply with quote

BasicFox wrote:
http://be.farnell.com/texas-instruments/sn74lvc1g126dckr/logic-74lvc1g-buffer-driver-sc705/dp/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-rectifier/irf7307trpbf/mosfet/dp/1374975

i.e. IRF7307TRPBF
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