Encoder for Boebot using CNY70

Skywalker49

Hello,

I want to make encoders for my Boebot and since the wheels are directly srewed on the servo's axes,
there is no room to mount an encoder wheel onto the axes.

The alternative I have in mind is to use the CNY70 which is a "Reflective Optical Sensor" and can be
mounted at one side of the wheel. The sensor should detect the black and white sections on the
encoder "print" put at the inside of the wheel. I hope one get the picture :<))

Does anyone have experience with the CNY70 because I wonder how "reflective" the print
must be. Can I just use regular paper with black and white sectors as Mr. Whit showed to us
in his mail today?

Thank you,
Ed

Whit

skywalker49,

I guess you have seen the Parallax digital encoder - http://www.parallax.com/detail.asp?product_id=28107

You also might take a look at this. http://www.nubotics.com/products/ww01/index.html

You could print the encoder wheels on a reflective sticker as nubotics does - I'm not sure how what the CNY70 would need.

Good luck.

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Whit+


"We keep moving forward, opening new doors, and doing new things, because we're curious and curiosity keeps leading us down new paths." - Walt Disney

Skywalker49

Whit,

yes I'm aware of the Parallax encoder. As usual a lot of documentation and an advanced design compared to what I have in mind.
The Parallax set use the IR modulated signal and as a result is less or not sensitive to ambient light. My set-up is not that sophisticated.

But, it is difficult and costly to get Parallax stuff. There is one distributor in the Benelux and the minimum order is 250 Euro unless
one pays an extra 17 Euro for handling cost. The encoder cost 35 so .. I wait till Christmas and make a big order :<)))

In the meantime I will do some experiments.

Thanks for the reply and the black & white wheel layouts.
Ed

Dgswaner

Skywalker, I realize this is an old post but I'm kind of where you were when you wrote this. Do I buy the parallax encoders or do I make some? Except that I'm not using servos, I'm using large 12v motors. so either way I'm going to have to adapt something. I actually have one encoder working I'm using a salvaged IR emmiter-detector pair. but rather than use a encoder wheel I'm looking though the teeth of a sprocket. thats part works fine but I can't find any schematics to read IR sensor. and I'm not actually sure if the IR sensor is going to react fast enough because of the spacing of the teeth is so thigh. Have you come across any circuits or any other solution? anyone else have input?

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A complex design is the sign of an inferior designer. - Jamie Hyneman, Myth Buster

D Faust

Hall effect + magnet?

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--DFaust

Dgswaner

can Hall effect sensors have multiple magnets so the resolution would be better? I have 6" wheels so with only one magnet that would be a little to coarse.

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A complex design is the sign of an inferior designer. - Jamie Hyneman, Myth Buster

D Faust

Why not?· They just sense a magnetic disturbance.· As long as the feilds aren't close enough to eachother to make a constant magentic field, you can put as many as you would like.· If this is a problem, use smaller/weaker magnets.· The code would be the same as with a color wheel/ir beam breaker encoder.

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--DFaust

Dgswaner

do you know if that code just reads high or low pulses? does a hall effect sensor have to run through a transistor or some other circuit to produce signal?

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A complex design is the sign of an inferior designer. - Jamie Hyneman, Myth Buster

D Faust

I think in the user app section of the parallax website someone used a hall effect sensor fro a drill.· I an not sure of the circuit.· It should give a high or low pulse.· I have seen that they give a signal after the field begins to decrease (magnet passes sensor) and that it gives a signal in the pressence of a magnetic field.· I am not sure if this depends on the part or one of these is wrong.

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--DFaust

Franklin

Hall effects will also sense a metal (iron) object if they are backed by a magnet. They can detect grar teeth or sprocket cogs if properly placed and biased. If this intrests you do some online research (I don't know where I found this stuff)

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- Stephen

Dgswaner

that's pretty interesting, only problem is that my sprockets are plastic. I think I have some hall effect sensors that I salvaged from some where I think I'm going to give that a shot and see what happens, other wise I'll try the CNY70.

Thanks for all of the input.

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A complex design is the sign of an inferior designer. - Jamie Hyneman, Myth Buster