really cheap R/C servo tester ?

Is there a really cheap way to make an R/C servo tester that cycles it back and forth ? I'm talking less than 10 bucks.
I saw something at Lynxmotion or Parallax or somewhere like that for around $18.
Thanks ! JCD
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http://www.uoguelph.ca/~antoon/gadgets/servo3.htm
Michael
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Hi,
Why not a cheap atmel uC, a xtal and a poti. Have a look on my site under projects/ocau servo mod.
Not sure what it cost but I imagine it's only about 3-4Euro for all the components including the programming cable and the compiler (demo version of Bascom AVR - Max 4Kb code)
Regards Ian Dobson
Home of the Atmel based UDP mobile web cam http://www.planet-ian.com All mails scanned with av-filter.pl (F-Prot / perl)

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pogo wrote:

Hey Pogo, what exactly do you want to do with this thing? A really cheap servo tester, like 555 ckt, doesn't really tell you much, other than the servo will actually move. For this, I would actually recommend springing for a simple R/C airplane transmitter-receiver combination. Maybe $50-60 from tower hobbies, etc. If you get this, you will find plenty of other uses for the xmtr-rcvr in remotely controlling your robot, too. Every roboticist needs an R/C transmitter :).
For real servo testing, it helps to know the actual servo pulsewidths, so then you can calibrate servo-arm position vs pulsewidth, etc. For this you can buy one of the cheapo 2 or 4 servo controller boards, which operate via RS232. If you hunt around, I think there are some for under $20.
Also, you can check out Dennis Clark's page to roll your own servo contorller. He has code for use on a PIC12C508, which costs about $1 ....
http://users.frii.com/dlc/robotics/projects/botproj.htm
- dan michaels www.oricomtech.com =====================
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bucks.
All I want it to do is to rotate the servo back and forth. That's it. Nothing fancy. Just need to see if things work mechanically as desired, range of motion, etc. For anything else I can hook up the "real" servo controller, whatever that may be. Looks like I'll just stick with wiggling the wires for now !
Thanks !
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pogo wrote:

Just to wiggle it, a proper 555 ckt should do, ie generates a short pulse [1-2 msec] on a periodic basis [every 20-msec or so]. You just need to be careful that the pot settings won't be able to drive the servo horns into the mechanical stops and bash the gearing.
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pogo wrote:

About $20 is what it will cost for something store bought. The RobotLogic tester, which I've tried (works well) is also in the $19.95 range. I don't think you'll find much for less tgan this.
Otherwise you make one. If you add a second 555 you can get it to sweep automatically. Otherwise just do it manually. There is a 555-based servo tester in Robot Builder's Bonanza 2nd Ed (don't know about the third edition). Get a small solderless breadboard and build it on that. No soldering.
Since I also like to calibrate servos for centering, I invested in a Hitec HFP-10 servo tester/programmer. They aren't cheap -- about $150 -- but it does everything you need. And when you graduate to digital servos you can use it to program things like their speed.
-- Gordon
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Cool! I should'a looked ... I'm real bad about getting too used to seeing a book on the shelf and not picking it up! Thanks ! JCD
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Gordon McComb wrote:

Hey Gordon. I kept this post in the back of my mind for the past couple of weeks while I was working on a new doo-dad. You mention above that you calibrate servos for centering using the Hitec device, so I'm wondering ...
What my doo-dad does is to measure servo and other pulses from about 4-usec up to 65-msec. Has a 1-usec resolution/accuracy. What I found was that the servos on the Servo-Tank that I bought from you last month
are "centered" [ie, stop turning] at about 1525 to 1530-usec, while I was expecting something more like 1500-usec.
I'm pretty sure my doo-dad - I call it the Servo-Dog - is accurate, because I've tested it against both the output of a PIC PWM hardware peripheral, and also using PULSOUT from a BS2. Am I missing something here?
- dan michaels www.oricomtech.com =====================
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Haven't seen your doo-dad, and I'm not sure I want to! <g>
On the Parallax servos: those are factory set. I doubt they're right on 1500 us. The hole in the side of the case makes it easy to adjust. Only the ones I personally modify (the GWS ones) are calibrated to 1500, but even those might be off a few us. What is critical is an LCD display to show the pull rate.
As a commercial product there is some liability having something for RC servos that goes down to 4us. For an unmodified servo that has some torque that could strip out gear teeth. I don't like buying customers new servos, so I only recommend products I know will sweep within a reasonably "safe" range, which the Hitec programmer is designed to do. That's something for you to consider.
-- Gordon
dan michaels wrote:

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Gordon McComb wrote:

That's too bad, cause I'm gonna send you one, JFTFOI.
This is something I've had cooking for a long time, but just built it recently. Believe it or not, the spur that got me going now was reading a comment several weeks ago in your Robot Builders Bonanza about using a mode-display device on a robot. I've done this many times using separate leds, but decided it would be nice to have a display device that took a servo pulse as its input, and then be able to signal "many" different modes, and that you can see from across the room.
I need this thing for my hexapod, which hopefully is going to Robothon in Seattle. I'll be sending it and not going myself, and wanted an easy way for the guys to be able to select the proper mode for different situations - like play, calibrate sensors, compete, etc.

Yes, I notice the Servo Tank you sent has Parallax servos. They don't stop turning until at about 1525-usec, as noted last time, but at least
they are both set very closely.

I'm not sure what you mean here by "pull rate". On your tank the servos will pull the tank around in a circle when sending 1500- usec pulses to the servos. My doo-dad is named Servo-Dog and uses 7-segement led displays, BTW, with power supplied by the R/C receiver/servo-controller.

At present, S-Dog doesn't generate pulses, only measures incoming. It measures down to 4-usec, for general purposes. Next week, it'll generate pulses for test.

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dan michaels wrote:

I don't know what a pull rate is either! It was a typo. I meant pulse rate.

An all-in-one device is handy or otherwise people (like me) who regularly test servos have to keep a separate controller handy and programmed to do position tests or sweeps. It's nice to be able to just plug the thing in, dial up the "pull rate" and watch the servo go. Or not go, and that's the reason for the test.
-- Gordon
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dan michaels wrote:

FWIW, In my opinion the only truly effective method to stop a servo is to stop sending it pulses. This can be done with any microcontroller, but some serial servo controllers don't provide for this. When powered the output lines always generate a pulse. In this way they emulate a R/C receiver, which is fine for models cars and planes but not so great for modified servos.
The problem is that analog servos are sensitive to component drift, which naturally happens when the device warms up, as motors do, or when operating the servo under a different temperature than when it was calibrated for. I've seen my carefully tuned calibrations change by as much as 15us in just a couple minutes of operation.
Fortunately most folks don't try to use servos for granular speed control without the use of an encoder. Then you can have your microcontroller adjust the presets dynamically. It can be continually attempting to find the new center point as it drifts around.
-- Gordon
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wrote:

A google search for "servo 555" turns up links like below if you want to make a driver..
http://www.geocities.com/BourbonStreet/3220/servobasics.html http://archive.chipcenter.com/circuitcellar/october01/c1001rr1.htm http://www.seattlerobotics.org/encoder/200210/servoex/ServoExcerciser.htm http://www.schumacher.clara.net/servodriver.htm http://www.uoguelph.ca/~antoon/gadgets/servo2.htm http://www.uoguelph.ca/~antoon/gadgets/servo3.htm http://www.uoguelph.ca/~antoon/gadgets/servo4.htm http://home.earthlink.net/~tdickens/68hc11/servo/servo.html
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