seesaw sensor question

I am extremely new to robotics being 58 years old, but was hoping someone here might be able to give me some guidance;
I'm working on an idea that works much like a seesaw, is there a
sensor that would send a signal to a servo or other device that would work 180 degrees from the signal? Meaning if a seesaw was up this would send a signal to offset that motion in direct proportion to it wioth the intent to always keep it in a level state? I'm so archaic I was thinking that a rheostat might be able to do it but I do hope we are way beyond that device for this problem. Any and all help is greatly appreciated.
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Welcome to the club. :)

There are a range of options to do what you want. But the most useful for hobby-type work are sonar and infrared (IR).
An IR distance sensor can output a pulse or voltage level that's proportional to the distance between the sensor and some reflecting surface (such as the ground). They work up to 10 meters (usually at the expense of looking like a pair of binoculars) and usually give you a continuous output.
Simple sonar modules can do the same thing. But they are periodic and normally require a little bit more of control circuitry to set them off and interpret the output. Again, they typically generate an output pulse with the width proportional to distance, but many can also generate a voltage level, or even send a packet of bits that encode the distance as a small number. There are dozens of sonar modules around. They can work upto 10 m or so.
Both options are low-cost i.e. <20 USD many places.
Next you'll probably need something in the way of a microcontroller to read the output from your sensor and control some effector like a motor or servo. Typical of how many would approach this work are the numerous boards based on AVR8's. Want to learn some assembler programming and binary programming? You may need to.
On the effector side, you need a servo controller (cheap servos usually need a pulse of a certain width to move to a particular position in their range of -- say -- 0 degrees up to 100 degrees).
Some AVR8 boards may have control circuitry for a few servos, or you may need an extra little board -- usually about 10mm x 10mm for 1 or 2 servos -- to do the work via some kind of serial interface to the AVR8 board.
Not to give too much of a plug to anyone, but I've worked with Pololu parts for years and they are pretty cheap and have enough doc for most old codgers with tinkering-in-the-back-shed genes to make head or tails of.
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Rudyeb wrote:

There are a number of solutions. The one that will probably carry you the furthest forward is to start learning how to use microcontrollers. The microcontroller that seems to have the most "buzz" these days is the Arduino. If you live near a metropolitan area, I would recommend trying to find out if there is a local robotics club. That is an excellent way to get going. Failing, that join some of the robotics club mailing lists -- HBRC (Home Brew Robotics Club), SRS (Seattle Robotics Society), DPRG (Dallas Personal Robotics Group) and start asking questions. Failing that, visiting your local library and seeing what they have in starter books is worth doing. Many of got going via Gordon McComb's Robot_Builder's_Bonanza. You should seriously consider getting a subscription to Servo Magazine as well. This list used to be much more active, but it got seriously nuked a spammer and most people have left.
Enjoy,
-Wayne
P.S. Full disclosure, I'm currently president of HBRC; hence, my bias towards robotics clubs.
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Yes a rheostat would do the job, but the modern terminology would be a potentiometer for something at low power. If you were to take apart the servo motor in a radio control car, you would find that a potentiometer is used to measure the position of the output arm.
Modern hobby servomotors are available in a great range of strengths and speeds. You might even take one apart, and remove the potentiometer, or simply cut its wires. Then, measure the resistance of the original potentiometer, and find another with a duplicate value. You would mount this new potentiometer so that it connects to your seesaw. Then to make the whole system worm, you would need to feed the servo motor the correctly pulsed signal to stay centered. There are pre-made devices for this which were designed for the radio control hobbyist to test their servo motors.
I don't know your application, and the ones Mr. Gramlich mentioned the ultrasonic or infrared sensor might be a better choice since they don't wear out like the potentiometer would. Also, the servo motor I mentioned would constantly be drawing power if the seesaw experienced a constantly unbalanced load.
Joe Dunfee
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On 01/01/2011 08:41 AM, Joe Dunfee wrote:

...
An optical encoder (as used by pre-"laser" computer mice) might also be useful. http://en.wikipedia.org/wiki/Rotary_encoder
Depending on your needs, simple limit switches may suffice (they're also cheap and generally reliable -- see the buttons on your mouse). Limit switches may also simplify the circuitry if you do use a rotary encoder (otherwise you have to track the velocity). Tilt right until one switch is hit, then start tilting left.
Assuming the seesaw should hit both limits, the rotary encoder only adds a proportional control.
To avoid microcontrollers, a couple DPDT relays (or transistors) could implement the required switching. If your rotary encoder has a variable-voltage or variable-resistance output, then it could drive the gain of a transistor or other power amplifier.
- Daniel
P.S. Here's a nice internal view of a microswitch. http://en.wikipedia.org/wiki/Microswitch
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You probably just haven't told us enough, but based on your description, the best solution is to use glue. That is, glue the seesaw so it can't move. That automatically adjusts the force needed to keep it level. :) :) :)
(everyone else already provided you with "good" ideas).
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On 01/03/2011 01:22 AM, Curt Welch wrote:

In a similar vein: Attach springs to both ends of the seesaw. Or one spring to the center.
- Daniel
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