DC Motor Speed Controller for Green Power Racing Car


The racing industry has become of age due to the emergence, utilisation of technology in our industries and broad development of the machinery industries. Racing as a sport requires a machine or car with the variety of conditions in its engine built up, among them fuel, power consumption, speed, durability and above all the ability to generate power for maximum speed and stability (GEIGER1981, p. 50).  Therefore, the following report will develop a simplified view towards the development of a direct current (DC) speed controller for a green racing car. Technology in industries has provided a range of gadgets, which have never believed to have existed in the early 19th century. The inception of a DC speed controller for racing cars has extinguished advantages in the concept of providing power and speed to a racing car in the modern technological era.

Therefore, a number of principles, which have been incorporated into the development of this controller, are all covered in this report, which includes its ability to act under the laws of physics, such as its force principles, the principle of relating seed and speed regulations. Acceleration of the car as is it achieved through this gadget is called the DC speed controller of a racing car. Most of these principles and their mathematical formulas have been explained in relevance to how the speed controller works to achieve its optimum functionalities. The formulas of these basic functionalities have been resolved into simpler versions to achieve and create understanding of its principles. Relevant theories have also been included to provide the underlining basic information to explain the principles behind the DC motor that have been illustrated, (Alerich, WN & Herman 2007, p. 132)  Due to high demand for the power and safety for the environment and users, the race cars are being modified to adopt green sources of power. To develop green power driven vehicles, it is necessary to understand which role the DC motor played in controlling the speed of the race car in different operation conditions.


Motors have been part of machines with the sole purpose to produce electricity, which is used in the powering of powerful engines and electric systems of machines, which are used in the general domain in industries, our homes in generating electricity for various services and purposes. This makes the DC motors as the primary devices, which are used in the generating energy. These DC motor speed controller uses the basic principles, which are generally used in the torque or speed implemented mechanical loads. In the theory perspective, DC motors can be described in their functionality composition and integrity, but  developing the initial information, which shows the pictorial composition of the motors in the speed characteristics of any mechanical loads. As an electric motor, it is powered from direct current; however, the direct current in the runner is switched using the commuter to be a stationary space (GEIGER1981, p. 50).  DC motors also contain permanent magnets that are usually replaced with magnetic field that are windings for the creation of this magnetic flux region to attain a greater flux density and power control, as an example of defining the primary functionality.

For the input, there is electrical energy that is supplied from the source, while at the output there is mechanical energy. In different applications, the DC motors are usually used for the driving of the mechanical loads. Some of the applications of DC demand that the speed remains constant even as the load on the motor varies. In other applications, the speed is controlled over the wind range. These requirements of the speed indicate the importance of studying the relationship that exists between the speed and torque of the motor. In generating power to the mechanical parts of the load, mostly DC motor creates a trade-off between how fast the output shaft rotates and how much the torque of the motor supplies. This concept of DC power is applied in regard to the development of the motor engine of a green speeding car. The concept is to obtain the maximum speed and regulate the power in acceleration of racing cars.


A mechanical load with a perfect speed controller provides the optimum balance in the power generation towards the speed management. The technique in the development of this speed controller either DC or AC has the advantage of creating an efficient system, which makes a mechanical load to perform to its limits. The many specifications, which have been developed, have the designs to improve smooth throttle movement, minimal steady-state, optimal speed tracking, monitoring speed error, and robustness of the system variation. The complex status of the speed control algorithm has ever increased year after year so as to meet the demand on the stringent car performance. The earliest systems controlled speed in a fixed position (Alerich, WN & Herman 2007, p. 134). However, in 1950s the speed controller that had feedback system was developed. The enhancement that followed was the proportional control with the integral bias input, which minimised the steady-state error margin and reduced speed when the DC system was modified. It is with the recent development of microprocessors that more sophisticated speed control strategies have been adapted. The optimal LQ regulators, Kalman filters, and PID controllers have been developed and initialised.

The current work has been focused on the DC-based speed controllers in relation to their application in the race cars. Therefore, the complimentary development of the DC motors speed controllers in the mechanical development in the industry of mechanics has provided extra options in the performance of mechanical loads, which require sufficient energy levels in their movement loads (Graf, E 1985, p.57). The racing green car is the latest development with energy conservation principles, hence the introduction of the speed controller with the concept of DC energy, has positive principles, which not only help but promote the efficiency of the speed and speed regulation capabilities during movement and halting.

Green Power Racing Car

The green racing car has the same principles as the solar powered car, which was developed by the Solar Jackets racing vehicles in Georgia Tech. The difference is that the solar jackets’ cars covered their solar energy into electrical energy than converting direct energy into current, which can be used to power green cars in the speed regulations system. The motor control system that was applied was the primary electrical sub-system that was used by the green racing cars speed controllers (Graf, E 1985, p.57).  The principle of developing the solar-powered racer car in attaining a steady velocity through the cruise controlling feature has almost the same technique of application in the green racing car. This feature allowed the adjustment of speed and the braking system that is inbuilt towards the speed controlling system. In most cases, the electric motors may be subcategorised on the basis of the types of the voltage source that is used while driving them.

There are two key categories: AC and DC. There is also the third form that is referred to as brushless DC motor, which uses the DC voltage sources with electrical control, though the motor construction is mainly based on the AC motor principles. The DC motor is an electric motor that is powered from direct current. The direct current in the runner is switched using the commuter as a stationary space. The DC motor has a rotating armature that winds through the linking magnetic field. This defines different linking of the armature and field winding, providing different inherent torque/speed controlled characteristics. The direct current motor speed may be regulated through changing the direction of the field current or by varying the tension applied to the armature (Graf, E 1985, p.57).  The establishment of variable resistance in the field circuit or armature circuit allows the speed control.

The modern direct current motors are frequently controlled by the DC drives. The implementation of the direct current motors to operate machinery eradicated the necessity for the internal designed combustion engines or the local stream and line shaft drive systems. The DC motors may directly operate from the rechargeable batteries that provide the motive force for the electric driven cars (Alerich, WN & Herman 2007, p. 134). Currently, the direct current motors are still applicable as in the implementation of racing cars.

DC (Direct Current) Motors

Through the fixed voltages produced by the car battery system in the mechanical load of the racing car, it empowers the direct current motor in the speeding system (Alerich, WN & Herman 2007, p. 134).  The direct current produced by the battery is highly regulated, hence there is no secondary mechanism needed to regulate voltage but it’s exceptionally powerful to power the machine loads.

  • Force

Force is the mechanical energy that is produced by the mechanical loads through their winding and moving alongside each other creating a discharge of energy. The spontaneous emission of energy in the DC motor is caused by the magnetic field that is created by the generating output flux of magnets and the rotating rotor. The magnetic flux then is created by these rotating motors against the magnet that generate magnetic energy. The magnetic flux existing between the poles is used axially through the motor. The racing car requires greater performance from the components of its mechanical capabilities (Graf, E 1985, p.57).   In order to generate the amount of power needed in the development of this optimum energy, in DC motors, the batteries are used which in turn are regulated through the permanent magnets that are usually revolve around the magnetic flux region to attain a greater flux density and power control. The rotor consists of several loops of conductive wires. As the power current (I) moves continuously through these loop of the length (L) while in the presence of the magnetic field (β) it experiences the movement force (F) as formulated by the Lorentz Force Law.

F= I*L (β); where L=loop length, I= current and β= magnetic field.


Induced direction of flow of the loops in the rotor causes reverse in the direction of flow of the current in the motor. In order to produce maximum flow of current throughout the motor, the direction of the current should be reversed constantly throughout the rotation. The continuity of the process is maintained through the commutation brushes and by the slip rings (GEIGER1981, p. 50). Every brush is linked to the positive and negative side of the DC power source, while the slip rings carry the power current to the loops on the rotors.

Explaining the above diagram, Direct current motor with the exceptional development principles, which utilises the Lorentz force conversation principle, leads to the generation of the induced current in the production of reliability, low cost, and simplified control of the motor speed through the commutation brushes and force applied through its poles.


In the production of current by the DC motor and battery system, the energy is in electrical stage, which is then converted to mechanical energy induced into the production of power for the loads. The electromechanical energy conversion devices are essentially the medium used for transfer between the input and the output sides (GEIGER1981, p. 50).   There are three electrical machines that are (induction, DC, and synchronous) commonly used in the electromechanical conversion of energy. The conversion of electromechanical energy occurs when there is a transformation in the magnetic flux that connects the loops that are related to the mechanical motion.

For the input, there is electrical energy that is supplied from the source, while at the output, there is the mechanical energy (required at the load).

Speed and speed Regulation

In harnessing speed parameters of the DC motor of a racing car the generation of power and the forces behind its generation are relatively the most important aspects in parameters of interest in the speed regulation, which is defined as the variation of the speed as the full load is exerted on the motor (Alerich, WN & Herman 2007, p. 134). The formula for the speed regulation is given below:

Speed regulation (SR) = {(Nno load – Nfull load)/(Nfull load)}*100%; Where Nno load is the speed, where there is no load placed on the load, and Nfull load is the speed of the motor, when maximum load is exerted.

The above graph illustrates a torque/speed curve of the DC motor. From the graph, it can be induced that the speed of the output shaft is inversely proportional to the torque. Alternatively, there is a trade-off between how fast the output shaft rotates and how much the torque of the motor supplies (Alerich, WN & Herman 2007, p. 134). The motor characteristics are usually provided as two points of the graph:

a)      The No-load speed is the maximum output speed of the output shaft, when there is no torque that is applied to the shaft.

b)      The stall torque is the representation of the point on the graph, when the torque is at maximum, though the shaft speed is zero at this point.

The load on the motor determines the final operating point on the torque curve. As provided in the figure given below, when the motor in linked to drive the load, the interaction of the torque required by the load and the torque generated by the motor provides the point of operation.                                    

Power and Efficiency

By analysing the above diagram and the graph below it, Power in harnessing the speed in the mechanical loads of the racing car engine exists in two main conditions that are necessary for the production of force in the conductor. The conducting element must be conducting the current and ought to be located within the magnetic field. With the two forces exist, then a force will be applied in the conductor that will then move the conductor in a perpendicular direction to the magnetic field. This constitutes the basic theory, under which the DC motors operate (Graf, E 1985, p.57).   Technically in operational fundamentals in the power and efficiency are the outputs, which are generally converted from electrical energy to mechanical energy by the motor torque. In that case POWER=Torque*Angular velocity; and TORQUE =Force*Distance; moved by the load. Efficiency is the power output against input power multiplied by the % of efficiency. Therefore, increasing the power input will definitely develop efficiency of a mechanical load, especially that of a mechanical load.

Motor resistance

Resistance, which is provided by the torque effect in the DC motor controllers, results in the production of the magnetic field around the magnetic poles; this creates a reliable conduit in the power usage. Therefore, the magnetic field density and voltage, which flows with current (I) in the two coil ends, manages to create the force that would be exerted on the coil as a result of the loop due to the interaction of the magnetic field and the electric current. The exerted force on the both sides of the loop is such that the loops start to rotate in the force direction (Graf, E 1985, p.57). This in turn leads to the development of torque in the speed regulation and power production. Motor resistance is in turn associated with the throttle pedal, which increases the number of times the motor rotates and spins with the principle of draining power. The braking effect in the brake pedal regenerates the power in batteries, in turn it decreases the number of rotations of the motor, and hence deceleration takes place.  In the case of a racing power car, it has several controls, which are used to monitor the cruising effects of the mechanical loads like the voltmeters, speedometers, which show the degree, at which they have to maintain speed, gaining power and speed regulations, acceleration and deceleration.

Back (Electro Magnetic Force (EMF (E)

Due to many wires in the coils and the fast rotation of the motor in the mechanical load, it develops into the advantageous rotation of the motors enhancing the generation of power and its outside magnetic interference in the concept generating force, which in this regard manages to create a magnetic influx, which in turn induces EMF (E) (e) induction.

e = d?/dt

The induction of EMF (e) is illustrated in the diagram 3, below. The voltage is usually in opposition to the voltage that evokes the current to flow through the conductor and is referred to as the counter-voltage (back EMF (e)).

Diagram 3

Induced voltage in the winding of the DC motor

The value of the current that flows through the framework is dependent upon the difference between the used voltage and the counter-voltage. The current due to the counter voltage strives to oppose the same foundation of its generation according to the Lenz’s law. This opposition results in slowing down the rotor (Graf, E 1985, p.57). In due course, the rotor slows down sufficiently enough to the point that the force generated from the magnetic field equals to the load force that is exerted on the shaft. Eventually, the system moves at a constant velocity. 

Torque Developed

The equation for the torque generated in the DC motor may be derived as shown below:

The force developed on a single coil wire is formulated as;

F = IL*B

(Newton), where l and B are the vector quantities considering the B = ?/A, where A is equal to the area of the coil.

Given the above, the torque for the multiple loops with the framework current of la:

T = K?la

Where ? isequal to the pole/flux in Weber, la is the current flowing in the armature winding, and K is the constant that depends on the coil geometry (Alerich, WN & Herman 2007, p. 134).  The torque T is the function of the distance and the force, where F = IL*B lumps all fixed parameters to the constant K.

The mechanical power produced is the outcome of the mechanical speed of motion and machine torque, %u1FF3m,

Or Pm = %u1FF3mT, where T = K?la

The Induced Counter-voltage (Back EMF (e))

Owing to the spinning of the wire loop through the magnetic field, the flow connected with the charges at the different locations that cause the EMF (e) to be generated (Alerich, WN & Herman 2007, p. 134).

The induced EMF (e) generated in the single coil: e = d?c/dt

DC motor speed controller (speed driver)

The above Block diagram represents the DC motor speed controller that is commonly used in the electric race car. In this case, the DC motor speed is controlled by the microprocessor. The DC motor is difficult to control when compared to the stepper motor that can be controlled using the appropriate command (Graf, E 1985, p.57). The circuit, which is generally developed in the case of managing the power optimum in the developing in speed regulation and harnessing of power in the concept of acceleration and deceleration of the mechanical load.

The intelligent Controller Design

The intelligent DC speed controlling system ought to be designed to provide for a smooth ride and heftiness of the speed control system to changing operating conditions (Graf, E 1985, p.57). The block diagram that identifies the essential functional connections between the speed controller and the rest of the system in the race car is illustrated in the diagram below, (Krishnan 2010) 

From the diagram above, The controller is used as the interface between the car driver and the power sources (DC motor and IC engine). The driver controls the race car by applying pressure on either the accelerator or on the brake pedals. The DC speed controller responds to the commands given by the driver and selects the optimal operation condition for the race car combining intelligently the speeds from the both sources of power through the epicycle gear train. The feedback command chain is used in addition to record the actual speed produced by the DC motor.

The History of DC Motor Speed Controller

With the emergence of the solid state electronics in the early 1950s and with this technology becoming popular and affordable in the 1970s, the application of the pulse width modulation became more practical. The fundamental principle has been to retain the voltage at the full capacity (12 volts) and only altering the amount of time the voltage is supplied to the DC motor (GEIGER1981, p. 50). Most of the intelligent speed controller circuits require large transistors to allow the power on and off. There are various advantages of the intelligent speed controller, which include efficiency, longer lived DC motors and broader operational range.

All the advantages of the modern intelligent controller are the result of maintaining the voltage supplied to the DC motor at full capacity, which results in current being restricted to saving the limit for the loops (GEIGER1981, p. 50). For the future, the motor developers are working toward the pulse width modulation (PWM) integration to the intelligent speed controller to develop a hybrid speed controller systems. 


The speed controller in any mechanical load is a clear approach towards the next generation of consumption of power in the efficient cars like racing cars, which need optimum power in the development.

The current work is a representation of the modern approach to the driving race vehicle. The speed controller is developed on speed combining the capability of the epicycle gears connection (GEIGER1981, p. 50).   The signals from the brake, accelerator pedals, and the reverse button have been intelligently synchronised to generate the required input signals for the DC motor and the engine of the car. Technology in the efficiency of a mechanical load has been developed into the perspective of gaining more power used than the power lost in regard to efficiency of the engine.

In turn, the engine and the DC motor harmoniously control the speed of the wheels of the car depending on the characteristic equation and the command of the selected gear (Graf, E 1985, p.57). The design of the DC motor for speed control in the race car utilises the idea of hybrid race car. The system is designed in such a way that it does not require a mechanical braking subsystem that will reduce the cost of such cars.