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Subject: 
Re: Struggling with encoder wheel
Newsgroups: 
lugnet.robotics
Date: 
Fri, 13 Apr 2001 09:04:00 GMT
Viewed: 
1021 times
  
As I am not so purist, I think that an angle sensor based on a small
potentiometer (There's a description on Michael Gaspari's site) would be the
simplest solution...

But your absolute encoder is a challenge in itself! What about using two
side-by-side light sensors each discriminating between black and white,
instead of one trying to guess between 4 different levels (and trying to
find transitions between them too)? The number of bits is the same...

Or perhaps one looking at a b&w clock pattern while the other reads the 4
level gray value? (but this would give more calibration problems especially
with power supply variations due to ageing batteries or motors consumption)

Philo
http://www.philohome.com


In lugnet.robotics, Stef Mientki writes:
hi Chris,

Chris Osborn wrote:

In article <3AD6C92D.5C9AD92D@yahoo.com>,
Andy Gombos <gombos_2000@yahoo.com> wrote:
You could build a rotation sensor found on Michael Gaspari's site, using a
magnetic strip.  It is supposed to give 40 or so counts per revolution.

Yah, but if I'm gonna build my own sensors, there's a lot I could
do. I'm sort of a purist. I'm trying to stick with the stock sensors
so that most people can build a copy of my system. Printing out
something on a printer and gluing it to cardboard is something most
people should be able to do, without having to buy a bunch of special
things and special tools.


That's in fact a good principle.
Isn't it possible to improve the dynamic range of the light-sensor by taping the red LED, I read that somewhere but I don't know where.
Why not use a continuous grayscale, with pure with and black holes in it to get a continuous calibration ?
Or translate you rotation in a linear movement en using a pure black and white wedge ?


I've plans for several rotation sensors, but they will not meet your criteria ;-), here are some of mine ideas
- using a 10-turn trim potmeter (continuous, low friction, over 360 degrees, small)
- Hall sensor with a concentric moving magnet (continuous, no friction, 360 degrees)
- opto-transmittor with a rotating vane
- grayscale with calibration by using 2 or 3 detectors (inspired by you idea)


--
Chris Osborn                      Full System, Inc.
fozztexx@fullsystem.com           2160 Jefferson St., #240
http://www.fullsystem.com/        Napa, CA 94559
Webhosting that *works* - 99.99% uptime - First 3 months free

Stef Mientki



Message is in Reply To:
  Re: Struggling with encoder wheel
 
hi Chris, (...) That's in fact a good principle. Isn't it possible to improve the dynamic range of the light-sensor by taping the red LED, I read that somewhere but I don't know where. Why not use a continuous grayscale, with pure with and black (...) (23 years ago, 12-Apr-01, to lugnet.robotics)

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