Carleton University ELEC 3105 Project DC Motor Project Author: Adam Heffernan Student Number: 100977570 December 6, 2017
Contents 1 Introduction 2 1.1 Background of the DC Motor.......................... 2 1.2 Design Plan.................................... 2 2 Details of Design 3 2.1 Design Description................................ 3 3 Operation of Motor 3 3.1 Figures....................................... 3 4 Comments 4 4.1 On Trouble Shooting............................... 4 5 Conclusion 5 6 References 6 1
1 Introduction 1.1 Background of the DC Motor The DC motor was most famously presented by Michael Faraday in October of 1821. In this case the motor was simply a lab prototype, the power of the DC motor had yet to be harnessed for useful applications. It was a long time, approximately ten years before another British inventor known as William Sturgeon came along, and prototyped the first commutator rings. He had developed the first rotary motor, which practically had all the components of a modern day DC motor. 1.2 Design Plan At its most basic sense, a DC motor is attempting to turn electrical energy into mechanical energy with high efficiency. Low efficiency results in large power loss which is why some motors are not realistic to be used outside of a lab setting. The theory that is behind a DC motor states that whenever a current carrying conductor is placed in a magnetic field, it experiences a mechanical force. The direction of this force is governed by the left hand rule. The magnitude of the force is found from Equation 1. Using this theory, if we send a flow of electrons into a current carrying armature, which is adjacent to the magnetic field lines from the permanent or electromagnet rotational motion will begin. Using brushes and commutators allows us to switch the poles of the armature with every half rotation. If there was not a split ring commutator on the motor, the motors direction would have reversed on every half rotation as the result would be a north-north and south-south poles, which will try to repel one another. A simple design diagram for a DC motor is below. We will attempt to replicate something similar to this during our design. F = IL B (1) Figure 1: Basic DC Motor Design Diagram 2
2 2.1 Details of Design Design Description The design used is really very basic. It is a single phase DC motor. It consists of a copper electromagnet wrapped around a ferromagnetic iron core. This electromagnet is then placed through a piece of PVC tube where is has both ends sticking out, one for the North and South side of the electromagnet. The PVC tubing is then held up by a stand that has been constructed from wood, containing two copper fittings on each side that will loosely hold the PVC in place in order to reduce the friction when the pipe spins. Permanent magnets were then placed adjacently on either side of the copper electromagnet, the permanent magnets on either side need to be placed in order to attract one another. Next, two copper rings were cut to place around the one end of the PVC tubing. These two copper rings were glued to the PVC, and a space was left between both rings to allow polarities in the motor to switch with every half rotation. Finally two brushes made from paper clips were placed on either side of the commutator so that when the armature is at 90 we have contact from both brushes, as the motor spins the brushes will lose there connection with the commutator and the other brush will then touch that part of the commutator, in turn reversing the polarity of the motor with each half cycle. The design chosen is unique in the fact that it involves more than a paper clip and household magnets to put together, this does not seem challenging. 3 3.1 Operation of Motor Figures Figure 2: Picture of DC Motor Implementation 3
Figure 3: Picture of DC Motor Commutator Rings with Brushes 4 4.1 Comments On Trouble Shooting Our Motor did not work as expected. The resistance between the coils was measured to be 0.02Ω. Therefore the lab power supply was probably just shorting out the whole time. An attempt was made to add a resistor to one of the coils, in practice this should have worked to at least get the motor rotating. However the problem was the power through the resistor was much greater than 1/4W and therefore the resistor just blew up. When we attempted to use a battery to run the motor the terminals of the battery got very hot very quickly and it was not worth starting a fire just to see if the motor would run. The other potential issue with the design of the motor we used was the fact that the rotating bar that the copper electromagnet sits in has some slight friction when it is rotated. This is due to the fact that the bar is being held in by two copper fittings which are loosely holding the tube up. One last issue which was addressed in troubleshooting the motor was the addition of extra permanent magnets. In order to get the magnetic field strength of the permanent magnets as large as possible, more magnets were added to the apparatus in an attempt to get the motor working. 4
5 Conclusion In conclusion to this report, a great deal about the theory and operation of the DC motor has been obtained. The knowledge obtained during this project is the foundation behind all DC motors. Even the motors that Tesla engineers would have most of the same theory behind them. It is all about maximizing efficiency as mentioned in the introduction section. For this reason, our project would not be useful in industry and outside of a lab setting. Suppose even if we were to get our motor running. The efficiency of the motor designed would be much less than approximately 50% this is due to the fact that there is problems with the friction, signal loss, attenuation of the input current and so on. These are all issues that have been addressed in modern DC motor designs. 5
6 References (1) Electrical4u.com. (2017). Working or Operating Principle of DC Motor Electrical4u. [online] Available at: https://www.electrical4u.com/working-or-operating-principleof-dc-motor/ [Accessed 7 Dec. 2017]. (2) Daware, K. (2017). How a DC motor works?. [online] Electricaleasy.com. Available at: http://www.electricaleasy.com/2014/01/basic-working-of-dc-motor.html [Accessed 7 Dec. 2017]. (3) Solarbotics.net. (2017). DC Motors Background and history. [online] Available at: http://solarbotics.net/starting/200111_dcmotor/200111_dcmotor.html [Accessed 7 Dec. 2017]. 6