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Unread 29-02-2004, 23:23
Rickertsen2 Rickertsen2 is offline
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Re: Optical Sensors Used as Encoders?

Just me 2 cents, but if you are going to go through the trouble to do all this, then why not just use encoders or gear tooth counters?

If you use reflective tape and banner sensors, it will work, but i don;t see how you can possibly get much resolution.
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Unread 29-02-2004, 23:38
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Re: Optical Sensors Used as Encoders?

Quote:
Originally Posted by Rickertsen2
Just me 2 cents, but if you are going to go through the trouble to do all this, then why not just use encoders or gear tooth counters?
Mostly because our team has a serious lack of $$$ and time, and since we have the banner sensors and can easily acquire some tape or white paint to put on our wheels, it's worth the try. And we're hoping that with enough 'markers' we can get it accurate enough for our purposes....

Thank you everyone for all of your help....
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Unread 01-03-2004, 00:44
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Re: Optical Sensors Used as Encoders?

Personally, I think unless the bot is very slow, the extra resolution wont matter. You still cant stop the bot theres just too much inertia. And we are not using the sensor on the actual wheel. We have it on a gear that is in a ratio of about 18:1 to the wheel. So that increases the resolution. And about the tape... The rules say "no adhesive-backed tape on the robot. The only exception is electrical tape, and it can only be used as as insulator". So a "decorative" explanation might not go over with the inspectors too well. White paint works very well, and is completely legal.
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Unread 01-03-2004, 07:59
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Re: Optical Sensors Used as Encoders?

We used Banner sensors last year for wheel encoders and have included them this year as well. We use a custom wheel so when the wheel was being assembled we just slipped a piece of dark papaer between the spokes of the wheel. By using two encoders (outlined above) you can tell direction and distance traveled. Last year we were able to get accurate down to at least an inch which made auto mode pretty easy. You need to couple the wheel sensors with a direction device to really know where you are.
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Unread 01-03-2004, 16:41
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Re: Optical Sensors Used as Encoders?

Last year we used banner sensors and tape marks, but this year we went ahead and spent a whopping $80 for shaft encoders (300 clicks per revolution ... as opposed to the 8 at best we had before).
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Unread 01-03-2004, 17:36
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Re: Optical Sensors Used as Encoders?

Quote:
Originally Posted by Greg
Personally, I think unless the bot is very slow, the extra resolution wont matter. You still cant stop the bot theres just too much inertia. And we are not using the sensor on the actual wheel. We have it on a gear that is in a ratio of about 18:1 to the wheel. So that increases the resolution. And about the tape... The rules say "no adhesive-backed tape on the robot. The only exception is electrical tape, and it can only be used as as insulator". So a "decorative" explanation might not go over with the inspectors too well. White paint works very well, and is completely legal.
I read all the First Questions and answers last night and they said that reflective tape for pulse generation is legal. As long as they don't change their minds like they did with the yaw rate sensors life will be good.
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Unread 01-03-2004, 17:34
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Re: Optical Sensors Used as Encoders?

Quote:
Originally Posted by Rickertsen2
Just me 2 cents, but if you are going to go through the trouble to do all this, then why not just use encoders or gear tooth counters?

If you use reflective tape and banner sensors, it will work, but i don;t see how you can possibly get much resolution.
Not counting slop in the chains, I'm predicting .3 in resoulition We will be testing and codeing on a drive mock up built with some unused but gorgeous double bearing blocks and last years Cim motors. Hopefully we can make it all work in our "Drive system lab"
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Unread 01-03-2004, 17:36
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Re: Optical Sensors Used as Encoders?

Quote:
Originally Posted by Rickertsen2
Just me 2 cents, but if you are going to go through the trouble to do all this, then why not just use encoders or gear tooth counters?

If you use reflective tape and banner sensors, it will work, but i don;t see how you can possibly get much resolution.
lol we dont need 1/4 degree resoluton. we need to know GENRALY how many times the wheels have turned...
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Unread 01-03-2004, 21:44
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Re: Optical Sensors Used as Encoders?

Quote:
Originally Posted by jacob_dilles
lol we dont need 1/4 degree resoluton. we need to know GENRALY how many times the wheels have turned...
Well, it shouldnt be hard to figure out w/ the code example i posted. Let me know if it comes in handy
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Unread 01-03-2004, 23:47
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Re: Optical Sensors Used as Encoders?

We tested the banner sensors to measure RPM's, and from what I saw it worked quite well, but our team decided to go with shaft encoders.

We also were going to use a potentiometer to measure the position of our arm, but also went with shaft encoders for that since the potentiometers from RadioShack were only responsive over about 180 degrees of their range, and we needed the full 270 degrees. We could have geared down the potentiometer, or gone with higher quality potentiometer, but we already had the shaft encoders.
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