Wheel encoder question.

Rontopia

ok. so.. im not sure where to start.

I have started putting together a new bot.. its got all kinds of goodys but what it doesnt have is any kind of wheel encoders. now its going to be a while before I need them but it got me to thinking about them, how they wrok, who makes good ones, and so on.. the base im using is http://www.lynxmotion.com/Category.aspx?CategoryID=57·with 12 volt motors. so what would· be good encoders for this base and please keep in mind that this bot will go outdoors although not in any real rough areas.

the next question/observation I have is this.. has anyone made a optical incoder? something like the optical mouse your using? just seems like a good idea.

thanks for you time



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IC layout designer
Austin Texas

Joe "Bot" Red

Hey Muahdib.. nice Lynxmotion base!!.. one thing I see is that it looks like you will have to modify the back of the motor in order to add the wheel encoder to the shaft of the motor, something along these lines:

http://www.geology.smu.edu/~dpa-www/robo/Encoder/pitt_html/encoders.html

Exactly what brand/model of motor are you using???

A while back I was experimenting with the possibililty of using the Propeller MOUSE.SPIN object with an old optomechanical ball mouse for measuring wheel speed/direction. the information is posted here:

http://forums.parallax.com/forums/default.aspx?f=25&m=159746

Although it worked really good during my testing, I haven't done much since, but I will try to take pictures of the whole assembly and post it here this week, this idea works with the Propeller, and it should work on a PC based robot (if I recall correctly, you are planning on using a Mini-ATX motherboard)

I hope this helps.... Happy Roboting...!!... Jose

Rontopia

well right now im going to use a propellor.. i have not given up on the miniATX but it seems that its just easyer to use the porpeller to run the motors and sensors and basic choices with.

I will look in to your post in a bit.. just dont have the time at the moment.

thanks for responding, and I will be back soon.

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IC layout designer
Austin Texas

Rontopia

ok.. joe.. sorry it took me so long to get back. i am in the middle of tape out and am super busy at work. infact, I dont really know was the last day I had off. I know it was several weeks ago.. wow.

anyway..

the motors are the exact same thing as what coms with the kit.. only diff is that they are 12v and have a little higher gear.. 200rpm's at the shaft. other then that if you look at the motors in the base kit you would not be able to tell any difference at all.

I was also thinking about this last night and I thought of another idea. what about having a smaller roller that rests on the top of the 2 back wheels? the roller would have a shaft that runs over to the top deck of the base and into some kind of encoder. seems easy but I know its not. but in that way i could use some old electronics from the inside of an older roller ball mouse. hmm..

anyway.. just waitiin on them pics man..

Rontopia

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IC layout designer
Austin Texas

Joe "Bot" Red

Hey fella.... uhmm.... I believe the idea of using a roller to sit on top of the wheel could be more difficult to deploy and who knows, depending on the use of the robot.. stuff can get stuck between the wheel and the roller... it appears as a more difficult idea to deploy to me... I was looking at the assembly instructions for that 4WD base, and I believe you might be able to attach the encoder wheel right next to the wheel hub... there should be enough gap between the wheel and the body of the robot in order to attach the encoder wheel ..... I created a crude drawing that I am posting here.... let me know what do you think...

I will take the pictures tonight.... I promise...

Post Edited (Joe "Bot" Red) : 7/10/2007 8:18:42 PM GMT

Joe "Bot" Red

Hey .. here are the pictures, this was taken from a Logitech 2-button wheelmouse, basically, I carefully cut off the sensors assembly in one piece with a dremel tool, and then I reconnected it with flexible cable.... the cables are difficult to solder because the copper layer on the pcb is really thin and separates from the pcb if you apply too much heat / pressure...

Anyway... after you are done, you simply use the MOUSE.SPIN to read back the values of axis X and Y.... Something I like about this idea is that you can also solder switches to where the button switches are and sense the status of the switches too, if you have a wheel mouse, then you have the possibility to sense 3 switches (the 2-buttons + the wheelmouse press button)... so... you can sense 3 rotary encoders + 3 switches using just 2 pins on the propeller... nice !!!

Happy Roboting!.. Jose

Post Edited (Joe "Bot" Red) : 8/14/2007 5:36:42 PM GMT