[SOLVED] How to make a robot go straight?

My bot has two rear wheels connected to the motors and a castor wheel in the front.
How domake it move in a straight path.
1) Should i make use of a ultrasonic sensor and make it follow a wall?
2) I have read online that rotary encoders can be used too. I did understand the concept but unable to figure out how to help. Can someone guide me on this.
3) Should i replace the castor wheels when two front wheels. They wont be connected to motors but then i guess they will make the bot more stable with respect to direction. But then it will make turnings difficult since they cannot be controlled in any way(as they are not connected to motors).
So Castor wheel or Two Front wheels?

First you should learn basic clearly....there are lot of sources available in EBooks As per this forum rules,i'm unable to share over here, so kindly refer Ebooks in internets.

Without some idea of the size and shape of your robot it is difficult to advise.

You should be able to steer with just two wheels as long as they are spaced apart at 90 degrees to the forward line of the robot. Just introduce some difference in motor speed and it will turn toward the slower one.

There are many ways to sense direction and distance but unless you are experienced in design, I would suggest you keep it simple and use a 'line follower' optical system. Ultrasonic does work but consider the effects of objects in the path and reflections from multiple surfaces and the way the echoes will confuse the robot.

A rotary encoder is just a disc that turns on the motor shaft or on a 'jockey wheel' (a wheel driven from motion along the ground) and it feeds back the speed and possibly the number of rotations (= distance coverered) to the controller. It is one option but they tend to be specific to the overall design and difficult to make as a one-off.

Brian.

Hi,

On a plain surface....and assuming both wheels have same diameter..
Then both wheels need same RPM.

With stepper motors this is easy.
With BLDC it is easy, too, because they usually have haal sensors inside, where one can get speed information.
With brushed DC it is difficult.
Without position sensors one can improve speed control by measuring voltage and current.
With sensors it is easy.

But as soon as the floor is not plain, then it is becoming difficult. Equal speed is not enough to ensure straight movement.

If you need more help, then you need to give more detailed informations first.

Klaus

I am trying to build an AGV. I don't want to make use of line follower concept. Instead I want to map the surroundings into a 2d array.
I have realised that any algorithm that i develop will not work unless and until my bot moves in a well defined path.
Right now i am working just on the prototype. Size :- 17x15 cm Shape :- Rectangular

Right now I am thinking about using ultrasonic sensors. I will always try to maintain a constant distance from the wall. This will ensure that the bot is moving in a straight line.
But then as it starts venturing into the area, distance from the wall will reduce, detection will become difficult. I will have to use something else.

Hi,

If you need further help, you need to give useful informations.

Klaus

KlausST said:

Hi,

If you need further help, you need to give useful informations.

Klaus

Click to expand...

Like what?

Hi,

Re-read our posts ... and see what we don't know.

Motor type, accuracy, is the surface plain, do you have position information, what algorithm did you try...?

Klaus