OpenServo.com

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

Jay,

Thanks, Mike sent me that sketch, but didn't include dimensions. The problem is that even though Jim did that sketch, I don't think he put much effort into thinking about it - if he had, he would have a better plan than shrink-wrap and wire ties. I'm pushing Jim and everybody else who might use that new servo motor, to think about what will work best, because I would like to see a good design done.

A good design accounts for the system it lives in and if a design doesn't, more often than not, it just ends up being a hack. I have nothing against hacks, its just that they don't make good products, because they generally cost more and don't work as well. The difference between a creating a hack and creating a good product is often just a little more thought.

BTW, it is never safe to assume. Smile

Cliff

ginge · Posted: Fri Jun 01, 2007 3:26 pm Post subject:

Cliff,

robotjay · Posted: Fri Jun 01, 2007 4:18 pm Post subject:

ginge · Posted: Fri Jun 01, 2007 4:26 pm Post subject:

Jay, Cliff,

Jim sent me a PM asking what is going on over here. I suggested we feed back as much as possible through Mike, who can liaise with Jim directly regarding general status etc. Anything more technical, like Cliff's questions over mounting brackets/placement etc are fine ok to ask over on the lynxMotion forums (like Cliff is doing).

Barry
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ginge · Posted: Fri Jun 01, 2007 6:21 pm Post subject:

I have done a quick mock up of the mounting options.

I like the idea of using a daughterboard. If we went with that we could use the ISP header as a connector.

Ignore nearly all part placements at this time. I have not started the real work of laying it out properly. This is a rough idea based on the sketches from Jim Fry. I have added a few mount points, one on each corner of the board, 5 for the heatsink, and 6 for the daughterboard mount.

Top part placement. The caps are near the power connector.

Bottom part placement. Plenty of space for the FETs

Daughterboards could be a couple of sizes. We could also go for both mount options to allow for small and large daughterboards

An idea of the heatsink placement. There is plenty of space for copper pour heatsinking.

As I said, very rough jotting down of ideas.

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

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

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

robotjay · Posted: Fri Jun 01, 2007 7:50 pm Post subject:

I agree with this approach. It'll allow Jim to know our progress via forum, without having to wade through all the technical details of how we arrived at that revision level. Is it possible to hyperlink to just a specific post within a thread? Or will he still have to search through the posts for a specific heading or something?
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mpthompson · Joined: 02 Jan 2006 Posts: 650 Location: San Carlos, CA

If you get the message id, it is possible to hyperlink to a specific message as shown below:

http://www.openservo.com/Forums/viewtopic.php?p=2949#2949

This link above goes to Barry's message regarding mounting options.

-Mike

ginge · Posted: Fri Jun 01, 2007 9:45 pm Post subject:

Here is revision 0.7.

This adds back the PWM connector (as you probably already noticed above) and also incorporates the NDS351 regulator protection.

Other than possibly changing the connector scheme, I would say we are very nearly there. I am sure Cliff has some more to add Wink

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

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

Barry, how about the PWM input being a two pin connector rather than a three pin connector. Most servos have a +5/6v input on the third wire and in this case we have a +5v output. I think it would be better to leave it off (or unconnected) than risk having someone accidently connect it to voltage.

Also, the signal from an RC controller isn't technically PWM. I would suggest changing the name from "PWM" to "RC Pulse" as that name is a bit more accurate and seems to be in use for such an input signal.

-Mike

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

Mike,

ginge · Posted: Mon Jun 04, 2007 8:19 pm Post subject:

All,

It has just come to my attention that the original schematic fished from my design archive (post 1 on this thread) is seemingly a copy of a from a product by Andras Tantos of Modular Circuits. More specifically this:- http://www.modularcircuits.com/h-bridge.htm

It is only fair that I attribute the correct sources to bridge portion of the derived design to the rightful owner; Andras Tantos.
Also note that the uModule is covered under a commercial license, and subsequently the first schematic (pg1) is not suitable for use without the the significant changes detailed above. The changes that Cliff has outlined will mitigate us from any potential trouble inferred by the original license.

Because of this oversight, and what this could have meant for OpenServo I feel it prudent to hand the torch over to Cliff, who has what it takes to make this all a reality.

Apologies if anyone feels cheated by me, I am genuinely sorry if that is how you feel. I will in future pay due care and attention to source listings in any designs in my archive that may be based on another.

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

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

Folks, I'm very sorry for this bump in the road. However, the good thing about open development is that such issues can be spotted and corrected as they occur. It's important that we all remember that nobody here is in it for the money and glory and none of us is immune to mistakes. We are all contributing in various ways because we feel we can lend a helping hand to a project we think is worthwhile. Let's please remember this as we move forward.

-Mike

poor-robot · Joined: 09 Mar 2007 Posts: 45 Location: Portland, OR

Not to throw another stick in the spokes, but doesn't the TPS76150 provide what we're looking for? The combination of the current limiting and the reverse diode should protect it, no?