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Turning a Robot From 90 Degrees

Can any one give an idea to make my robot turn exactly 90 degrees ???

I am using Tamiya Dual Gearbox & My robot is a tracked Robot

 

Any clue ???

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One of the robotics books I have read mentioned something about the use of multiple sensors so that if one failed the robot would not be without that sense. In your case would it not then be useful to keep the compass and add wheel encoders and/or steppers? This way if you know your heading from the compass and you tell the motors to spin the robot 90 degrees you can check the compass and then decide if you have in fact turned 90 degrees.

In My project I am trying to replace the tasks done by a Digital Compass By using other means like a Gyro + Some Coding & All , & Yes I support the idea of multi sensors & I am using that in my project Thankx for the response My Friend

But You see in my project I am trying to replace the Digital Compass, Since My robot is a kind of path finder when I Give the coordinates for it to travel it will do it on a virtual Cartesian plane ( imaginary), So in order to make it go straight always I am trying to turn it by 90 degrees always & By doing that I am ensuring that it would always go in a straight line, ( after meeting an obstacle it would turn 90 degrees to a suitable obstacle free side & then carry on to meet the coordinates I have given)

So I need a suggestion with out a digital compass & In my project I can use a Gyroscope ( Yaw Axis) & I am not much aware of Encoders as I haven't used them before, Any good tutorials on those ????

What about using Servos ( hacked) to drive the Tank instead of stepper motors , are they powerful & fast enough to drive my robot

 

why do you want to replace the compass? what is wrong with it?

Well there is nothing wrong with a digital compass My friend , I am just trying to find an alternative way to replicate the tasks of the Digital Compass using a combination of programming & other Hardware Inputs

So if any of you have any experience using gyro's with picaxe just let me know ok

 

Well you didn’t say anything about having a digital compass in your original post so we are trying to help you based on the little information you gave us.
With this added information I can’t see any way past having either some sort of encoder or using stepper motors. The gyro won’t help you much sins you have to know how long you have traveled each way to get back on track.

One fun way of doing this would be to have some sort of arraignment underneath the robot that would lift it up, turn it 90 deg and then set it down again.

For optical encoders, just Google a bit. Like http://abrobotics.tripod.com/Ebot/using_encoder.htm 
 


Sorry for the lack of information on my first post Sir, It was my very first post here So pardon me for that & yes I have been thinking of that fun way of doing the turn too ( I have seen it on some toys ), & it is on my option list but i consider that as my last resort. So this is what I am planning to Do right now 

1. Use a wheel encoder to calculate the distance traveled 

2. Use a Single axis gyro to sense the rotation of the Robot platform & turn it using PWM untill I get a 90 Degrees Turn

 

As I mentioned before My project is based on replacing the Tasks of Digital Compass When traveling to a Given Destination & I read & googled about the use of stepper motors & Thankx for enlightening me on that aspect

So what are your Ideas about using the Gyro on this matter

A gyro seems like a complex way to go, though I cannot claim to have any experience on thi.

Take a read through this wikipedia entry:

http://en.wikipedia.org/wiki/Inertial_navigation_system

There may be some hobbist systems available. Some quick googlings showed me this:

http://members.toast.net/joerger/gyro.html

Good luck.

Thank you indeed, I will be reading those things & Update the status here as a help to others who may follow these things, Any way keep helping me on this matter when a problem is raised ok

Have anyone tried to use an optical encoder on the tracks and not on the wheels. Somehow I think that would give a more accurate reading as the number of track ‘blades’ probably are higher than the number of lines one can put on the small wheels.
Probably much easier to build than a wheel based encoder.
And if the driving wheels are regular rubber wheels relying on friction the track encoder would eliminate that as well.