Magnetic Rotary Position Sensors

The Magnet and Hall sensor device arrangement has been used for retrospective feed back on servos like in the open servo project.

In the case of Servos the feedback was normally a standard resistor which obviously got worn out using the hall sensors for feedback got rid of this problem.It may well be worth looking at what they did since it's open source.

Hi John, thanks for the suggestion, 

There's a few interesting links I found via the "Open Servo Project" and there's lots of useful advice to read from there too.

http://hackedgadgets.com/2008/11/19/open-stepper-project/

http://www.jaredharvey.com/

The Open Server forums do discuss hall sensors in detail and also the chips I've been looking at here.  They even have a project called the "Open Encoder" which looks at these chips in detail so many thanks for the mentioning that project

http://www.openservo.com/forums/viewtopic.php?t=766

http://www.openservo.com/forums/viewtopic.php?t=940

Cheers

Andy

I'm glad you found it useful. The chappy has a good line in 3D printers and Hexapods as well so his site's worth a look at.

Also he does custom code for hire so there might be a solution if this project is more comercial.

Also if you have a reduction drive driving the table you could measure the angular change at the drive motor end  and since that rotates many times for each rotation of the table you will get a corresponding improvement in accuracy.  Another idea is maybe to use 2 mag sensors and thus average the values between them somewhat reducing the noise floor?!

have a look at my blog on the guy doing the optical alignment ..you may be able to get some ideas from here too

hope that helps... John

Cheers John, will look at that video for optical localisation. I did think about using two sensors to compensate for accuracy. As it stands I have no space for a reduction drive but perhaps I might have room for one in a second version.

I found a technique/algorithm for the averaging around 360° http://rosettacode.org/wiki/Averages/Mean_angle so that should be easy to port to my microcontroller.

Cheers John, will look at that video for optical localisation. I did think about using two sensors to compensate for accuracy. As it stands I have no space for a reduction drive but perhaps I might have room for one in a second version.

I found a technique/algorithm for the averaging around 360° http://rosettacode.org/wiki/Averages/Mean_angle so that should be easy to port to my microcontroller.

The optical video did give me a slightly more low tech idea for calibration.

If I mount a laser pointer on the device and have a scale along a distant wall then I should be able to accurately measure angles, like this:

http://www.robotroom.com/StreamHawk-Wireless-Explorer-Robot5.html

Indeed often you need to rethink the problem until it can be implemented with the kit at hand or with alternative methods ..good call