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sahasrara
01-02-2011, 01:29 PM
what is the simplest way to achieve perfect right angle turns in a black-white line follower bot?
i ve used a microcontroller program for it but that slows down the bot:( . i also tried used shaft encoder...but any method simpler than those???

pratheek
01-02-2011, 03:31 PM
Simplest option is to use a fairly constant power input for your motors and powering them only for a certain period of time, such that the robot turns 90 degree. You will have to calibrate and experimentally figure out the time for which you will have to keep the motors powered. You will not get perfect 90 degree turns but it should do the work.

For better results, power only one wheel while turning and that too at a slow speed it will reduce errors and jerks will stopping.

vikas
01-02-2011, 07:54 PM
If you can spend a little , Build a quad Omnidirectional wheeled robot

http://www.karankamdar.com/omni-directional-robot

@prateek

Time based turning never works :) .

Diffrential drive with encoders will also work when programmed properly , look at 3pi robots for easy example and code.

http://www.youtube.com/watch?v=mJV-KDqHgDQ

asimov_18
01-02-2011, 10:21 PM
I would call an omni wheel "an over kill" for a line follower. There could be other strategies to implement 90 turns. How abou the drive wheel turning in a vertical axis using a gear motor?

Asimov

allbits
01-03-2011, 10:38 AM
"perfect" right angle may not be achieved in simple ways. If it is a line follower, I dont understand why you need perfect right angles. Because, if you are navigating a right angle curve, the robot may not be navigated at exact right angle - because, the orientation of the robot may not be necessarily aligned to near perfection at the beginning of the right angle.

Look upto good algorithms. you need microcontrollers for line followers if you need to navigate lines with acute as well as obtuse angles, or in cases where lines overlap. There is no need for an encoder if the rules do not require you to memorise the line and go for a 'fast run'.

A few tips -
1) minimise hardware error. - Check this - run your robot straight for 2 meters. Without any controller or control. See how much deviation the robot has after 2 meters. Minimise that error as much as possible.
2) Cover up the sensor arrangement.
3) Place the sensor array close to the driving wheel. Not too close, not too far either. The optimum distance pretty much depends on the speed at which you are driving the motors.
4) Use a spiral line to test your bot. You can see the variation in the error adjustment as the radius decreases.
5) Place the load ( batteries/boards etc) symmentrical with respect to (left-right)sides. Place batteries/heavy components on top of driving wheel(s) to improve friction.

vikas
01-03-2011, 11:57 AM
Omni wheels will give almost perfect right angles with little effort. They are not an over kill if you are trying to win a competition ( Nothing is).

Also i believe the OP wants to do line maze solving. If it is so , look into 3pi code and constructions with the video link in previous post.

Other wise allbits tips will also help you do good.