# Servo Control without Computer



## Master__Gracey (Oct 16, 2008)

I will start with saying I have searched the forum already and have found some projects that are 90% there to what I'm after, but maybe someone can help me fill in the rest. I have a usb servo controller and software that already works just fine. My problem is that I'd like to take my prop off the computer. I'm looking for a way to record the PWM signal from the usb controller and later play it back exactly without the computer attached. I have seen recording and playback with a pot but never an existing signal. I have a PIC starter kit so I can possibly use a pic /eeprom combination to do this but I'm a very early beginner of such endeavors. I'm also open to easier methods if they exist. I'd like to get several minutes of recording which may limit the pic's abilities. If I could trigger other events when it starts playback that would be a great bonus. Thanks in advanced!


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## HomeyDaClown (Oct 3, 2009)

Three issues you'll have to deal with:

1. Capturing the serial/USB data stream (with some mechanism for timestamping it along the way)

2. Storing the captured data (flash drive / SD card...)

3. Playing it back in real time (re-syncing the serial/USB data stream to it's original record time)

Even basic netbook computers do this well with a little software.
Doing it on a microprocessor base would take some work.

That's why Brookshire's RAPU device is a litte pricey.

Another option would be to sample the position pot voltage from each servo but you'd still have to time stamp and re-sync.


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## Atom058 (Sep 20, 2009)

Gracey - I built a 4-servo recorder that sounds like it does exactly what you are trying to do. I did it for the same reason. It will hook in-line from the computer to your servos. When you get your routine on your computer just like you want it, you just trigger my board to start recording, start your playback and it will simultaneously record up to 4 servos for >10 minutes. When it is done, you just stop recording, unhook your computer and the board will then replay the routine every time it is triggered. I even have a version that will allow you to dump the whole routine onto a single EEPROM and then put this on a small dedicated playback board for deployment. This also allows you to make several copies of the same routine, if you want...


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## fritz42_male (May 5, 2009)

Atom, I was going to build a Picaxe version of what you are describing but if you have already done it then why re-invent the wheel. Can I get more info?

Also has anybody considered making their own Rapu from an Arduino?


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## Master__Gracey (Oct 16, 2008)

Homey- I have a usb to servo controller already so I'd only have to record the servo signal.

Atom- Do you have more info or links? Sounds like an existing solution!


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## Allen H (Feb 13, 2010)

I use the micro maestro boards from polulu, they are triggerable and run a sequence.
http://www.pololu.com/catalog/category/12


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## ouizul1 (May 22, 2010)

Dang, Allen...you've got a bigger bag of tricks than Felix the Cat. ...awesome.

Do you have an example of how big (i.e # of servos vs. time) of a sequence the micro will handle?


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## Atom058 (Sep 20, 2009)

Fritz/Gracey - I have a 2-page cut sheet (Word) on it, but I'm not sure how to get it to you. Should I PM it to you? Sorry, I'm a newbie at this stuff...


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## Master__Gracey (Oct 16, 2008)

Atom058 said:


> Fritz/Gracey - I have a 2-page cut sheet (Word) on it, but I'm not sure how to get it to you. Should I PM it to you? Sorry, I'm a newbie at this stuff...


You can certainly PM me or you could try to host it somewhere like rapidshare and post the link for everyone


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## Allen H (Feb 13, 2010)

For what I needed I got about a 4 min loop out of five servos. I had a good bit of down time between movements though, between 5 and 15 seconds.


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## fritz42_male (May 5, 2009)

That's the problem with the Polulu - limited memory. My Picaxe version was going to use an eeprom for the servo data.


Atom, I've got the document off Halstaff. Can you give me more info as to costs, components etc


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## Atom058 (Sep 20, 2009)

Hello again - I think I have figured out how to upload an attachment - this is the 2-page document describing the servo recorder that I built. Let me know if you have any questions... Thanks!

(Also just figured out how to get notified when there is activity on this thread, so I should be responding a little faster!):googly:


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## Master__Gracey (Oct 16, 2008)

Atom - Looks perfect. Are they available somewhere or are they a diy deal?


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## Atom058 (Sep 20, 2009)

Gracey - I can build these for you. Please contact me at [email protected] for details... Thanks! Jeff


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## ouizul1 (May 22, 2010)

Allen H said:


> For what I needed I got about a 4 min loop out of five servos. I had a good bit of down time between movements though, between 5 and 15 seconds.


Thanks. That should be way more than sufficient for my future needs. The price is nice, too.


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## Master__Gracey (Oct 16, 2008)

Do we think that an audio recorder would be capable of recording and playing back servo signal? I would think the only restriction would be if it has enough resolution. I've seen alot of sound recorders being built online and I wonder if a plug change so that instead of a stereo plug you have a common and a servo signal would work.


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## Atom058 (Sep 20, 2009)

Gracey - I'm not sure how that could easily be done. A servo signal is a digital signal that is either a logic 0 (0V) or a logic 1 (5V). The lengths of time that it is at 1 or 0 is what controls the positioning of the servo. You wouldn't be able to just feed that into an audio recorder (which takes an analog signal) and play it back without a lot of additional circuitry and software to encode and decode the signal... At least I am not aware of way of doing this...


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