ROBOTICSSTUDENTS:Fabricio Reyes M A01670714

ContenidoPrinciples of motors.......................................................................................................................2

Difference between AC, DC, Servo, Stepper and RC Servo motors................................................2

How do you size a motor?.............................................................................................................5

EQUATIONS................................................................................................................................5

Given a problema, how do you determine torque load?...........................................................6

What parameters do you need to solve for to size motor?.......................................................6

CONTROL....................................................................................................................................... 6

What are speed curves?............................................................................................................6

How do you control torque?......................................................................................................7

How do you control speed?.......................................................................................................8

How do you control position?....................................................................................................8

Electronics..................................................................................................................................... 9

What is the circuit to control a DC motor with a microcontroller?............................................9

What is the circuit to control a stepper motor with a microcontroller?..................................10

What is the circuit to control an RC Motor with a microcontroller?........................................11

Run through a hypothetical example based on one of the systems. Describe the problem. Run through the calculations..............................................................................................................11

Find commercial components......................................................................................................13

Motors..................................................................................................................................... 13

Drivers......................................................................................................................................14

Controllers............................................................................................................................... 15

How do you connect these three.................................................................................................18

Bibliography................................................................................................................................ 19

Principles of motors

A motor is a type of machine that is able to convert electrical energy into mechanical energy. This is done by a magnetic field, created along a wire when a current goes through it. If this wire is then placed alongside two magnets, then the temporary magnetism created by the magnetic field will cause a force on the wire, causing it to rotate. [1]

Motors are vastly used, and can be found in cars, drills, fans, Blu-ray and DVD players, washing machines, wind turbines and robots, among many other.

Difference between AC, DC, Servo, Stepper and RC Servo motors

To broadly differentiate motors, they can be categorized as AC and DC motors. The basic difference between this to motors is the type of current that is applied to them. The AC motors use an Alternating Current while the DC motors use a Direct Current.

Due to the armature construction, DC Motors have the capability of modifying their speed according to the amount of voltage that is applied to them, making them highly useful in applications where the motor speed has to be controlled externally. DC electric motors have many moving parts, and are very expensive to replace, which is why they are now being replaced for an AC alternative with a separate speed controller (variable frequency drives) [2].

Figure 1 - Simplified diagram of an electric motor

There are many different types of motors branching from these two types, Electrical KnowHow has a chart categorizing the different motors. [3]A brushed DC motor is an internally commutated electric motor designed to be run from a direct current power source. They are widely used in toys, and their main advantage is their inexpensiveness, ease of use and vast amount of sizes. [3]

Figure 2 - Pulse Width Modulated Variable Frequency Drive

Figure 3 - Different Types of DC Motors

Figure 4 - Brushed DC Motor

Since brushed DC motors have several disadvantages, such as wear, sparks (explosions) and noise produced from the brushes, the brushless DC motors have been gaining popularity, since instead of having brushes for commutation, they are electronically commutated. Electrical KnowHow offers a table showing the features of both types of DC motors. [4]Induction motors are the most common motors used in equipment, they have no need of brushes, since voltage is induced in the rotor. In Synchronous Motors, the rotor tries to line up with the rotating magnetic field in the stator, and are often used in systems that use a lot of electricity. Since Synchronous motors are more complex, they are not as widely used as Induction Motors. [5] Finally, a linear motor is an “unrolled” version of a motor, so instead of producing a torque force, it produces a linear force along its length. [6]

Among the AC and DC motors, we also have the Servo, Stepper and RC Servo motors:

Stepper Motors don’t continually rotate like usual motors, to be able to do this continual rotation, you would need to constantly turn on and off the coils for the shaft to move. Stepper motors rotate in steps, and each step is a fraction of a full circle, in degrees. They are also bidirectional. This can be seen in Figure7.One of the primary advantage of this motor against the others, is its capability of maintaining a position.

Figure 5 - Different types of AC motors

Figure 6 - Servo Motor, Stepper Motor and RC Servo Motor

Figure 7 - Stepper Motor Operation (Half Step)

Servo motors and RC Servo motors, unlike Stepper motors, do not move in steps. Servo motors have two cables, if attached to a power source it will start spinning. Servo motors are also bidirectional and the speed depends on the amount of load the motor is on.

RC Servo Motors on the other hand, have 3 wires (+V, ground and control), the control signal is a pulse of around 50 Hz, and the width of this pulse, commonly controlled via a PWM, determines the position of the motor. [7]

How do you size a motor?

Properly sizing a motor to your needs is important for efficiency and energy savings. Motors are most efficient when they are 90-95% loaded. If you under load a motor, energy is still being wasted, there is no benefit in buying a big motor and just under loading it. On the other hand, if a motor is overloaded, it will draw more current than what it was built for and thus, excess heat will be produced, shortening the motors life and also causing some safety issues. [8]

EQUATIONSIn order to successfully accelerate a load, the motor must develop and maintain more torque than what is required. This can be calculated by the following Formula [9]:Inertia is the property where a body offers resistance to any change in its rest or motion state, and

in order to calculate it, the following formulas can be used [9]:

Once the torque has been determined, the brake horsepower can be found with the following Formula [9]:

[13] http://www.designnews.com/document.asp?doc_id=228478

Given a problema, how do you determine torque load?The idea is to calculate the toque that a motor needs in order to move.If the load increases then more torque is required.First you have to calculate the necessary torque

T=F∗d

Then, you have to express the speed wanted for the vehicular and calculate the angular speed.V=ω∗d

Finally you can calculate the power needed for the system.P=T∗ω

These equations are used in the practical problem resolved later.

What parameters do you need to solve for to size motor? Max stator current Max voltage supported Nominal Voltage Nominal angular speed with no load Nominal angular speed max load Time overheating Max temperature supported

CONTROL

What are speed curves?

For a fixed voltage input from a battery, the speed of the motor is reduced as more load is added to the shaft. When the motor can’t move because of the load, the speed is zero, and the motor produces a stall-torque (ST), which is the maximum. Also, the current drawn from the battery is the maximum and the motor is heating. This should be avoided to preserve the energy of the battery. On the other side, when there is no load, the motor moves freely at the maximum speed, the no-load-speed (NLS). A balance between the two is called the operating point [10], and the curves may change between motors.

Fig. 8 Speed Curve

http://elpaso.apogee.net/md/mfcttor.asp

http://people.ucalgary.ca/~aknigh/electrical_machines/induction/basics/trq_speed.html

How do you control torque?

Torque is proportional to the current applied to the DC motor, in direct proportion. This produces the torque-current curve characteristic to each motor. To control the torque one needs to control the current at a constant load.

Fig. 9 Torque vs Current

How do you control speed?

The speed in a motor can be regulated by using the PWM technique on the supply voltage. The speed is in direct proportion to the duty cycle, being the maximum at 100% duty cycle. A closed-loop control can be used to regulate the speed to a given reference, using a speed sensor (tachometer, encoder), and a microcontroller. The encoder, for example, gives pulses of electricity that contain all the information we need to implement a closed loop control. The frequency of those pulses is directly proportional the the speed of rotation of the shaft (RPM) and the number of those pulses correspond to the angular displacement of the shaft. [11]

Fig. 10 Feedback lose loophttp://www.me.ua.edu/me360/spring05/Notes/Topic17-AC_Motor_Speed_and_Other_Motors_sv.pdfhttp://www.physicsforums.com/showthread.php?t=618236http://www.discovercircuits.com/DJ-Circuits/simplepwm2.htm

How do you control position?To control position we can use the same principle that applies for speed, and use a closed-loop control using an encoder as a sensor for the feedback. By counting the number of pulses it generates, and number of slots of the encoder, we can know how many degrees has the motor turned, which is its position. From there, a microcontroller can create a signal to move the motor to the desired position.

Fig. 11 Potentiometer used as position sensor

Electronics

What is the circuit to control a DC motor with a microcontroller?

To open-loop control a motor with a microcontroller an H-bridge is needed to provide the negative voltages needed for the motor to go the opposite direction. As can be seen in the image [12], the circuit needed is the connection between the H-bridge with the motor and the microcontroller. It is important to note that the H-bridge provides the power to the motor trough a different voltage source than the 5V needed for digital processing, because if they were the same the high current could damage the digital systems. Having this connected is a simple matter of programming the A and B pins to move the motor.

Fig12. MOTOR DC CIRCUIT

http://www.electronicsforu.com/electronicsforu/circuitarchives/view_article.asp?sno=472&id=4687#.U_K5Evm-2Fwhttp://electrosome.com/dc-motor-speed-control-pic-pwm/http://lfymag.com/admin/issuepdf/Const-2.pdf

What is the circuit to control a stepper motor with a microcontroller?If bidirectional control is required, then you need to have the same number of H-bridges as coils the stepper has. If no bidirectional rotation is needed then the circuit can be built with transistors like this [13] for a 4-coil stepper motor, were the pins 3, 5, 7 and 9 are the outputs of a microcontroller that go into hex-buffers:

Fig13. STEPPER MOTOR CIRCUIT

The simplest way to operate a stepper motor with a microcontroller is with the full step pattern shown in the table. Each part of the sequence turns on only one transistor at a time, one after the other. After the sequence is completed, it repeats infinitely until power is removed [13].

Q1 Q2 Q3 Q4

+ - - -

- + - -

- - + -

- - - +

http://www.imagesco.com/articles/picstepper/03.html

What is the circuit to control an RC Motor with a microcontroller?

Fig14. RC MOTOR CIRCUIT

A RC Servo motor needs energy (battery) and a PWM signal in order to control the position of the motor.

Run through a hypothetical example based on one of the systems. Describe the problem. Run through the calculations. PROBLEM:There is a structure of an electrical wheel chair for people that need help to walk.It has two DC motors but they do not know how to make it work.

SOLUTION:It is necessary to implement two H-Bridges, one for each motor. There are chips that implements tow H-Bridges in one package.

A microcontroller is to be used in this problem in order to capture signals form a Joystick and send signals to the inputs of the H-Bridges.

A Battery is essential to make everything works.

Fig15. CIRCUIT SOLUTION FOR ELECTRICAL WHEEL CHAIRLet’s design a chair for 80Kg person max.There are two motors so each one has to support 40Kg.The radius wheel is 7cm

T=F∗dT ,torque

F , forceor weightd ,∈this case isradius

T=40 kg∗10m

s2∗0.07 m

T=28 Nm28 Nm is the torque for each motor.

V=ω∗dV , speedd , radius

ω ,angular speed

For a desire speed of 0.5m/s

ω=Vd

ω= 0.50.07

rad /s

ω=7,14 rad /s

P=T∗ωT ,torqueP , power

ω ,angular speed

P=28 Nm∗7.14 rad /sP=200 W

That’s the energy that the battery has to give to the system.

Find commercial components

MotorsDC MOTOR

POLULO MOTORS

Fig16. POLULO MICRO MOTORS

Micro metal gear motor25D mm gear motor37D mm gear motorhttp://www.pololu.com/category/51/pololu-metal-gearmotors

SERVOMOTORHi-Tech Motor

Fig17. RC MOTOR

HS-65HBHS-65MGhttp://hitecrcd.com/products/servos/micro-and-mini-servos/analog-micro-and-mini-servos

STEPPER MOTORNEMA17

Fig18. STEPPER MOTOR

2 Coils motor 3000 rmp maxhttp://sine.ni.com/nips/cds/view/p/lang/es/nid/203936

DriversDC MOTOR-STEPPER MOTOR

H-BRIDGE 298

Fig18. DC MOTOR DRIVER

https://www.sparkfun.com/products/9670

NOTE1: L298N Driver controls 2 DC Motors or 1 stepper motor (2 coils)NOTE2: Servo motors have controllers included so in order to make them move it is necessary a PWM signal.

ControllersPIC microcontrollers

PIC microcontrollers are finding their way into new applications like smart phones, audio accessories, video gaming peripherals and advanced medical devices. Microchip provides solutions for the entire performance range of 8-bit microcontrollers, with easy-to-use development tools, complete technical documentation and post design-in support through a global sales and distribution network.http://www.microchip.com/pagehandler/en-us/family/8bit/

Fig19. PIC MicroController

Arduino microcontrollersArduino is an open-source electronics platform based on easy-to-use hardware and software. It's intended for anyone making interactive projects.http://www.arduino.cc/

Fig20. Arduino Controller

AVR microcontrollersWith ease-of-use, low power consumption, and high level of integration in mind, Atmel® AVR® 8- and 32-bit microcontrollers complement Atmel's ARM® microcontrollers and microprocessors to deliver a unique combination of performance, power efficiency and design flexibility.http://www.atmel.com/products/microcontrollers/avr/default.aspx

Fig21. AVR controller

Overload and Overheat ProtectionFuses are used to protect circuits, motors and controllorers.Capacitors parallel connected to amotor helps to reduce noise produced by motor movement.

Fig22. CERAMIC CAPACITOR

Fig23. FUSES

How do you connect these three

There is a 16F628A pic microcontroller that sends PWM signals to the inputs of the Hbridge L298 in order to control a dc motor.The L298 driver includes circuit protection with opto adopters. Thus design includes fuses for overload protection and a capacitor connected to the motor to reduce noise in system.

http://itp.nyu.edu/physcomp/Labs/DCMotorControl

http://www.talkingelectronics.com/projects/H-Bridge/H-Bridge-1.html

Figure 1 - Simplified diagram of an electric motor.........................................................................1Figure 2 - Pulse Width Modulated Variable Frequency Drive........................................................1Figure 3 - Different Types of DC Motors........................................................................................2Figure 4 - Brushed DC Motor..........................................................................................................2Figure 5 - Different types of AC motors.........................................................................................2Figure 6 - Servo Motor, Stepper Motor and RC Servo Motor.........................................................3Figure 7 - Stepper Motor Operation (Half Step).............................................................................3

Bibliography

[1] C. Woodford, "Electric motors," Explainthatstuff, 30 May 2014. [Online]. Available: http://www.explainthatstuff.com/electricmotors.html. [Accessed 18 August 2014].

[2] R. Chamberlin, "Difference Between AC and DC Motors," Precision Electronic Industrial Solutions, 23 May 2013. [Online]. Available: http://www.precision-elec.com/difference-between-ac-and-dc-motors/. [Accessed 18 August 2014].

[3] Electrical KnowHow, "Classification of Electric Motors," Electrical KnowHow, 2013. [Online]. Available: http://www.electrical-knowhow.com/2012/05/classification-of-electric-motors.html. [Accessed 18 August 2014].

[4] Electrical KnowHow, "Classification of Electric Motors Part II," Electrical KnowHow, 2013. [Online]. Available: http://www.electrical-knowhow.com/2012/05/classification-of-electric-motors-part.html. [Accessed August 19 2014].

[5] Electrical KnowHow, "Classification of Electric Motors Part IV," Electrical KnowHow, 2013. [Online]. Available: http://www.electrical-knowhow.com/2012/05/classification-of-electric-motors-part_22.html. [Accessed 19 August 2014].

[6] Electrical KnowHow, "Classification of Electric Motors Part V," Electrical KnowHow, 2013. [Online]. Available: http://www.electrical-knowhow.com/2012/05/classification-of-electric-motors-part_24.html. [Accessed 19 August 2014].

[7] R. Arrick, "The Difference Between Stepper Motors, Servos and RC Servos," Arrick Robotics, [Online]. Available: http://www.arrickrobotics.com/motors.html. [Accessed August 22 2014].

[8] R. Barnett, "Determining Load Horsepower, Wiring, and Breaker Size for Safe and Efficient Installations," Fluke, 2014. [Online]. Available: http://www.fluke.com/fluke/caen/community/fluke-news-plus/ArticleCategories/Plant-News/how-to-properly-size-motors-for-given-load.htm. [Accessed 22 August 2014].

[9] DAE Systems, "How do I properly Size a Motor?," DAE Systems, [Online]. Available: http://www.trinertia.com/pdf/How_do_I_Properly_Size_a_motor.pdf. [Accessed 22 August 2014].

[10] HyperPhysics, "DC Motors," HyperPhysics, [Online]. Available: http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/motdc.html. [Accessed 18 August 2014].

[11] Freescale, "Motor Principles," Freescale, 2014. [Online]. Available: http://www.freescale.com/webapp/sps/site/overview.jsp?nodeId=0ST2BDF5DC55DC9. [Accessed 18 August 2014].

[12] Electrical4u, "DC Motor or Direct Current Motor," Electrical4u, [Online]. Available: http://www.electrical4u.com/dc-motor-or-direct-current-motor/. [Accessed 18 August 2014].