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• Calculating Mechanical Power Requirements
• Torque – Speed Curves
• Numerical Calculation
• Sample Calculation
• Thermal Calculations
Calculating Mechanical Power Requirements
Physically, power is defined as the rate of doing work. For linear motion, power is the product of force multiplied by the distance per unit time.
In the case of rotational motion, the analogous calculation for power is the product of torque multiplied by the rotational distance per unit time.
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Selecting a DC motor for a particular application can be a rather involved process . Hower, it is often useful to be able to "ballpark" a motor selection on one's own. A few rules relating to the physics and the practical application of motors should be kept in mind.
The major constraint on motor operation is thermal in nature. The heat a motor must dissipate can always be calculated as follows:
Heat dissipated = current through the motor squared, multiplied by the terminal resistance.
The current through a motor is solely determined by the torque the motor produces. Current and torque are related by the torque constant of the motor.
Current through motor = torque produced divided by the torque constant
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DC Motor Application Considerations
Audible noise is a concern in some types of motor applications. In many medical applications like infusion pumps or prosthetic devices, the patient can be very sensitive to the noise disturbance. Good design practice requires that the noise be limited as much as possible. In large machines, the combination of hundreds of DC motors and gears operating simultaneously can be very loud and distracting to the employees who have to work in close proximity to the machine.
Quality Components: Probably the best method of insuring low audible noise in motors is to specify quality components. Motors using cheap or poorly fitted bearings are more likely to be noisy. Poorly designed or loose fitting brush sets can contribute to audibly noisy commutation. Manufacturers of inexpensive, high volume motors cannot reasonably be expected to concern themselves with quiet operation beyond some minimum standard, and the use of such motors in applications where quiet operation is important should be considered carefully. The designer must consider whether low cost takes precedence over quiet operation in the priorities of the customer.
Bearing Choice: The use of ball bearings without pre-load is a potential source of audible noise. Where the specific application permits, ball bearings should be pre-loaded. This means that the balls will not be able to move axially in the race and cause the minute intermittent rattling that can sometime be associated with unpreloaded ball bearings. Smaller ball bearings can be sensitive to heavy shaft loads. They are easily damaged during press fitting added components and by short radial or axial overloads. Care should be taken not to exceed the shaft loading ranges specified in the datasheets. A damaged ball bearing can be a significant source of audible noise and can effect motor life.
Stepping motors can be viewed as electric motors without commutators. Typically, all windings in the motor are part of the stator, and the rotor is either a permanent magnet or, in the case of variable reluctance motors, a toothed block of some magnetically soft material. All of the commutation must be handled externally by the motor controller, and typically, the motors and controllers are designed so that the motor may be held in any fixed position as well as being rotated one way or the other. Most steppers, as they are also known, can be stepped at audio frequencies, allowing them to spin quite quickly, and with an appropriate controller, they may be started and stopped "on a dime" at controlled orientations.
For some applications, there is a choice between using servomotors and stepping motors. Both types of motors offer similar opportunities for precise positioning, but they differ in a number of ways. Servomotors require analog feedback control systems of some type. Typically, this involves a potentiometer to provide feedback about the rotor position, and some mix of circuitry to drive a current through the motor inversely proportional to the difference between the desired position and the current position.
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If you're anything like me, when you run into a little programming problem you just trot down to the library and pick up a couple of books/manuals on whatever it is you need to master. Do a little reading and POW! You've got the tools you need. When I ran into problems with my firstRead More
These are another kind of DC motors ,but with a built in gearing Feedbck System. These servo motors come in many varieties and can from 0 to 180 degrees. Some rotate through a full 360 degrees or more.
They are extremely popular with RC plane,boat and Robots with precision handling like arms and legs.
And most of all these do not need any motor drivers circuits
A thing to note is that servos are unable to continually rotate, meaning they can't be used for driving wheels. There is a modification provided to do so at Society of Robots
Method to Drive a Servo
The servo normally has Three wires with it. Connect the black wire to ground, the red to a 4.8-6V source, and the yellow/white wire to a signal generator (such as from your microcontroller). Vary the square wave pulse width from 1-2 ms and your servo is now position/velocity controlled.
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Here we plan to list and describe some of the free & unknown software that can be used in place of famous & properitory software. OpenOffice-Openoffice is substitute to Microsoft office.It is open source and cross-platform. Gimp/GimpShop– A substitute to Adobe Photoshop which is an image editing tool. OpenLazio– An Adobe Flash like softwareRead More
Linux is an open source operating system.Linux is free.Linux being open source gives us advantage of customizing the linux and creating our own version.Various flavours of Linux have already evolved.Eg. Ubuntu evolved from Debian.Edubuntu(Educational version of Ubuntu) evolved from Ubuntu. To customize linux we have to tinker with source and recompile the kernel. Below areRead More
1. Nmap I think everyone has heard of this one, recently evolved into the 4.x series. Nmap (”Network Mapper”) is a free open source utility for network exploration or security auditing. It was designed to rapidly scan large networks, although it works fine against single hosts. Nmap uses raw IP packets in novel waysRead More
Military equipment, toys, communication, home electronics, computing, cars, satellites and others. This is only a partial list of products, which contain electronics.
Actually electronics won our world. We wake up with the ring of electronic clock, drink coffee from a electronic coffee machine, work with computers, learn by using video conferences, listen to the music from a sound system and go to sleep while adjusting our electronic watch for tomorrow morning.
It is hard even to think that only a hundred years ago our world seemed different at all from this point of view. But how did the electronics revolution begin? Which research and discovery was the basis for this modification? Why was it so fast, relatively to other developments in history? Let us Try to Answer these questions.
Theoretical and experimental studies of electricity started in the 18th and 19th centuries enabled the development of the first electrical machines and the wide use of electricity. During that time the first theory was founded and the rules of electricity was formulated. The event of identification of the electron in second half of 19th century by the English physicist J.J. Thompson and the measurement of its electric charge in 1909 by the American physicist A. Millikan were the point of turning the electronics evolution separately from that of electricity. Another coarse of interest to electronics was the observation of the American inventor Thomas A. Edison. He noticed that the current of electrons would flow from one electrode to another, if the second one was with relatively positive charge. This discovery led to the development of electron tubes. Electron tubes became very useful for manufactory at that time. X-ray tube, the radio signal detectors and transmitters, and the first power systems were based on electron tubes. The development of the vacuum tube and later the three-electrode tube by adding the grid between the anode and the cathode (Negative and positive electrodes in the tube) improved the characteristics of the tube by far and made it more useful for different electronic applications.
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