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View Full Version : Wheel position sensor positioning



Resilient
03-13-2009, 04:41 PM
I got wheel watchers (http://www.nubotics.com/products/ww01/index.html) and I am wondering how important it is to have them exactly centered on the axis of rotation.

Essentially, I can easily make it fit if it is 1/32" off center. I know if it were a single sensor, it wouldn't matter but this has two sensors that are set up to be the same distance from the center of rotation (I assume) and if its off center, they wont be. What kind of accuracy do I need when setting this up?

I would like it to be able to measure distance in a straight line with about +/- 2% accuracy and be able to complete a turn of 90 degrees with similar accuracy. I will also be using them to control speed and turning radius in a loop with other sensors.

Thanks
Jusitn

robologist
03-13-2009, 10:49 PM
I believe they include a sensor positioning jig, and do so for a reason. Essentially, if you want them to work, it would be best to adjust the frame they are going into, rather than trying to adjust the position of the encoder disk sensors. 1/32" is probably significantly more than one or 2 strips of the encoder wheel, in addition to causing a variable distance encoded as the wheel turns. This means that the wheel may read an encoder tick to represent 1 mm of travel on one part of the wheels circumference, while being 1.5 mm on another part. If it is able to read the strips at all while off center.

Resilient
03-14-2009, 01:34 AM
Yeah, the jig wont work with my setup. I am trying to mod it to fit a setup not driven by servos.

I am just trying to figure out how accurate I need to get it. Like do I need to get a custom jig made?

Sense it doesn't seem clear, I will probably try to get it closer than the 1/32" and see how it works. Then if I need to make a jig.