Some of the most handy electrical instruments that hold the pride of place in any workman's toolbox are the power drills. Learning to use a power drill was one of the first personal assignments that I took, when I used to assist my grandfather with odd jobs around the house. How the power drill operates to pierce through the toughest of walls and metal surfaces was a matter of mystery then. When I was introduced to the concept of an electric motor, during my studies in electronics, I finally figured out how the power drills operated.
About Cordless Power Drills
A power drill is an electrical instrument used to punch holes in walls and all sorts of tough surfaces. They can also be used to fix screws in walls and other surfaces. All power drills consist of a main body that houses an electrical motor, a handle to hold the instrument steady and the chuck mechanism which grips the drill bit. The controls include a safety switch, on/off switch, a speed control and a reverse switch. All heavy duty drills are powered by electrical power supplied through an attached electrical cord. The cordless power drills, that we talk about, in this article, are powered by Nickel-Cadmium (Ni-Cd) or Lithium ion rechargeable batteries. Let us see how these devices operate.
How Does a Cordless Drill Work?
The prime question that one must ask when understanding the working of cordless power drills are two. The first is 'What makes the circular torque motion of the drill bit possible?' and the second one is 'How does the drill get power?'. Let me answer the first question before addressing the second one.
The torque or rotational force driving the drill bit is supplied by an electric motor housed inside it. The working of the motor is based on the principle of repelling magnet poles. As you must have realized while playing with wall magnets, if you place two north poles of both magnets or two south poles of two magnets together, they repel each other. This is the very phenomenon that creates a torque in an electric motor, which is later translated into the motion of the drill bit.
A motor consists of a metal rotor mechanism, placed inside a permanent magnet. This rotor is a metal object wound with electrical wire. When the rotor is supplied with electric current, it turns into an electromagnet. The like poles of both magnets repel each other, providing a torque that turns the rotor. There is a switch mechanism provided with the rotor, also known as commutator, which keeps reversing the direction of current supplied to the rotor, that keeps it moving.
This generated torque is supplied to the gear transmission which drives the drill bit, via a rotating axle. Thus, the electric power supplied creates a magnetic field, which drives the rotor to provide the torque. By varying the power supplied and changing the direction of electric field applied, the rotational speed and rotation direction of the drill bit can be controlled.
To answer the second question, the power required for the purpose of driving the rotor is supplied by electrochemical cells. The reaction between metal electrodes and electrolyte mechanism within the cells stores and discharges electric current. The maximum torque that a cordless drill can deliver is dependent on the maximum voltage which the rechargeable battery can deliver. Cordless power drills come with installed batteries that deliver up to or more than 36 V of electric power. These drills can be operated where there are no direct power connection points, making them a necessary addition to a workman's tool box. That concludes our discussion on the working of the cordless drill.
The peculiar thing about mysteries is the way they turn into trifles, once you have figured out how they work. The electric motor based on property of magnetic fields that causes them to repel each other, is the motive force for the functioning of countless instruments like the cordless power drill.
Thanks to the development of modern electrochemical batteries and advancement in electronics technology, the creation of power drills and a variety of other 'unplugged' tools with rechargeable batteries has been made possible. So, the next time you use a cordless power drill and you feel it whirring in your hand while drilling holes in surfaces, you will now know what's happening inside and what's causing the whirring and the rotation of the drill bit.