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LA Robotics Club Message Board › Position sensor

Position sensor

Chris J.
user 11772561
Redondo Beach, CA
Post #: 7
You might have seen my intro in the other thread. Working on a punching robot.

There are low speed motors that turn a round "cam" and on the side of each cam is a wire that runs up to different parts of the arm. As the motors turn it pulls the wire, which pulls on the arm and makes it extend.

Works perfect. The trouble is that I never know where the arm is and I don't have the control with these motors that I would with servos.

I'm thinking something like a camshaft position sensor in a car might be good because it would tell me where the cam is and with that I can make a decent guess as to where the arms are.

Any ideas for a sensor? Maybe a simple laser with a small reflector on the cam so that when it reflects back I'll know the position? ??
Bob M
23122541
Sherman Oaks, CA
Post #: 9
Hall effect device (metal cam only) or opto-interrupter are my thoughts for your application. Either device is an inexpensive solution, but I might be tempted to try Hall effect 1st if the cam is metal. Opto-interrupters can be 'tricked' by outside sources of light and your cam has to be thin enough to fit between the opto's LED / photodector opening (or you could custom build a detector pair to size).

One last thought - You can read either sensor directly into an analog input pin and process what would be a 'sine wave looking' signal. If you want TTL level sensor inputs, you may need to add an op-amp to increase the signal output.

Hope that is of some help!
Tim L.
Tim_Laren
Granada Hills, CA
Post #: 1
You might have seen my intro in the other thread. Working on a punching robot.

There are low speed motors that turn a round "cam" and on the side of each cam is a wire that runs up to different parts of the arm. As the motors turn it pulls the wire, which pulls on the arm and makes it extend.

Works perfect. The trouble is that I never know where the arm is and I don't have the control with these motors that I would with servos.

I'm thinking something like a camshaft position sensor in a car might be good because it would tell me where the cam is and with that I can make a decent guess as to where the arms are.

Any ideas for a sensor? Maybe a simple laser with a small reflector on the cam so that when it reflects back I'll know the position? ??

People that attended the Arduino class and purchased one of my kits got a few of these http://hacker.instane...­. They are reflective sensors and they would work well. They are IR so ambient light should not be a problem. You can order them online or I will be at the TRW swap the last Saturday of the month. http://hacker.instane...­

Tim
Alex56782
user 17722901
Los Angeles, CA
Post #: 27
I was thinking about that too, you can use a reflective sensor, make an encoder, on the arm elbo (or more joints) or cam, use a A/D decoder to know the position. Or try a potentiometer on the elbo joint to read the position of the arm relative to the resistance it reads......
Tim L.
Tim_Laren
Granada Hills, CA
Post #: 2
I also have some rotary encoders that are pretty nice. They are like pots but produce 2 bit gray code. You could use something like this to detect motion and distance but would still require an index for home position indicator.
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