I'm designing a computer controlled toy, basically an arm that moves up and down. Only 90 degrees. I'm looking for some standard
electro-mechanical solution. I've looked up R/C servo motors. It certainly works. I've even got Servo + USB controller kit. However, (I'm not a mechanical engineer, mind you) it looks like an overkill for something that needs only two positions - 0 degrees and 90 degrees. Is there any widely used components (may be used in toys or robots) that provide this simple up/down kind of motion?
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You might try one of the little gear motors from www.solarbotics.com, they have several to choose from. You could then measure the current draw, and when the motor stalls or starts to stall you can stop it. Thus you wouldn't need limit swtiches.

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I feel I'm over my head with this thing, I'm software engineer and totally clueless about things like "draw" and how to measure it. Can you point me to some educational material so I can decipher your answer?
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The basic method is to put in a small value resistor in series with the motor. Then use a ADC or analog digital converter to measure the voltage drop across the resistor. if the voltage measured passes some pre-determined value (a increase in current beyond what is considered normal) you then turn off the motor. This would be the max limit points at each end when the motor reaches its stop point and starts to stall out. Also handy should someone stop the arm in midstride so to speak. The resistor is probably less than one ohm in resistance. Many MCU's nowadays have built in ADC's so this should not pose a problem. Most other MCU's have built in comparators which can also be used like this too. A number of small motor controllers have a built in current sense or current limiter sense line that might be handy for this as well. This might maybe help http://www.mathworks.com/products/demos/simulink/PowerWindow/html/PowerWindow1.html http://www.library.cmu.edu/ctms/ctms/examples/motor2/pid2.htm http://desyntwww.desy.de/~vstaa/teb/Hess_Manual.pdf A limit switch is basically a simple lever swtich at end end of the throw of the arm. When the arm reaches the swtich it tells the MCU to turn off the motor. Nuts and Volts magazine ran a series of articles on building and interfacing a linear arm unit a while back too. You might look it up.

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Thanks a bunch! This really helps!
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Do you remember by any chance in what year of Nuts and Volts this articles were published?
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On 28 Dec 2004 00:31:25 -0800, snipped-for-privacy@gmail.com wrote:

You can use a DC motor in a reversing setup. Near the bottom of the below page I've got a simple setup for a motor to be reversed using a DPDT relay, two big diodes, and two limit switches. You could control the relay via a parallel port pin using a resistor and an NPN transistor.
http://www.geocities.com/zoomkat/switch.htm