You must be thinking: what can we possibly learn about the vehicle that we don't already know? This may be true, but there are a few that we must make sure we understand before taking on this chapter. So, let's get started.Â
First is the chassis, which we will be using: it's is a four-wheel drive chassis and all the four wheels are independently controlled by a dedicated motor. Hence, we can change the speed of every single wheels as per our needs. We have chosen a four-wheel drive drivetrain as it is harder for it to get stuck on carpets and uneven surfaces. You can also opt for a two-wheel drive drivetrain if you want to do so, as it won't make a huge difference.Â
Now, once you assemble the chassis you might see that it does not have a steering mechanism. Does this mean that the car will only go straight? Well, obviously not. There are many ways by which we can steer the direction of a car while making small vehicles. The best one is called differential turning.Â
In conventional cars, there is one engine and that engine powers up the wheels; hence in principal all the wheels turn at the same speed. Now this works fine when we are going straight but whenever the car wants to turn there comes a new problem. Refer to the following diagram:
You will see that the wheels, which are on the inner curve, have a smaller diameter and the one on the outer edge has a larger diameter. You may remember a fact from elementary school: the larger the diameter the more the circumference, and vice a versa. Hence, the wheel towards the inner edge will be covering a shorter distance compared to the wheels on the outer edge at the same time, or in simple words, the inner wheels will be spinning slower and the outer wheels will be spinning faster.
This problem leads to the discovery of differentials in cars, which is a round lump at the center of the axle of the car. What this does is that it varies the rate at which the wheels are spinning based on the turning radius. Genius, isn't it? Now, you must be thinking: this is all right, but why are you telling me all this? Well, because we will do the exact opposite to turn the robot. If we change the speed of the motors on the inner and outer edge of the turning circle, then the car will try to turn towards inside and similarly if we do it for the other end then it will try to turn in the other direction. While making wheeled robot this strategy is not new at all. Steering mechanisms are complicated and implementing them on small robot is simply a challenge. Hence this is a far simpler and easy way to turn your vehicle around.Â
Not only is this way simple but it is a very efficient and simple strategy that requires minimal components. It is also better as the turning radius of the vehicle is also reduced. In fact, if we spin the opposite sides of the wheels in the opposite direction at the same speed then the vehicle will turn completely on its own axis, making the turning radius entirely zero. this type of configuration is called skid-steer drive. For a robot that is wheeled and works indoors, this is a killer feature.
