Guiding a Robot Through a Path

Question

I have a field filled with obstacles, I know where they are located, and I know the robot's position. Using a path-finding algorithm, I calculate a path for the robot to follow.

Now my problem is, I am guiding the robot from grid to grid but this creates a not-so-smooth motion. I start at A, turn the nose to point B, move straight until I reach point B, rinse and repeat until the final point is reached.

So my question is: What kind of techniques are used for navigating in such an environment so that I get a smooth motion?

The robot has two wheels and two motors. I change the direction of the motor by turning the motors in reverse.

EDIT: I can vary the speed of the motors basically the robot is an arduino plus ardumoto, I can supply values between 0-255 to the motors on either direction.

Answer 1

You need feedback linearization for a differentially driven robot. This document explains it in Section 2.2. I've included relevant portions below:

The simulated robot required for the project is a differential drive robot with a bounded velocity. Since the differential drive robots are nonholonomic, the students are encouraged to use feedback linearization to convert the kinematic control output from their algorithms to control the differential drive robots. The transformation follows:

where v, ω, x, y are the linear, angular, and kinematic velocities. L is an offset length proportional to the wheel base dimension of the robot.

Answer 2

One control algorithm I've had pretty good results with is pure pursuit. Basically, the robot attempts to move to a point along the path a fixed distance ahead of the robot. So as the robot moves along the path, the look ahead point also advances. The algorithm compensates for non-holonomic constraints by modeling possible paths as arcs.

Larger look ahead distances will create smoother movement. However, larger look ahead distances will cause the robot to cut corners, which may collide with obstacles. You can fix this problem by implementing ideas from a reactive control algorithm called Vector Field Histogram (VFH). VFH basically pushes the robot away from close walls. While this normally uses a range finding sensor of some sort, you can extrapolate the relative locations of the obstacles since you know the robot pose and the obstacle locations.