Can you get the speed below the rated speed by a field control method?
Speed range obtained by flux control technique is between 80 % to 160 % of rated speed. The max speed is limited by the design of the armature as at high speeds, the armature conductors may get damaged. So a safe limit of 160 percent is imposed. The disadvantage is the speed control below rated speed is in a narrow range. So armature voltage or supply voltage control method is more used. Dc supply voltage is controlled by something called 'chopper'.
Between armature control and field control, which is the best method of speed control?
You cannot decided which is best armature or field control. That all depends on purpose where the drive will be used.Say for DC motors (separately excited type) we usually go for field control if there is a field supply voltage equal to the rating of motor and you need to run the motor in fixed rated speed. Here field control helps adjust the speed for a small range. These are open loop system i.e you require some one to maually adjust field current. As setting it for closeloop will probably lead to unstable system as the range as is very small.On the other hand armature control provides a big range of speed control and these configuration is utilized for closed loop systems.Similarly for bldc there exist armature and field control algorithm. Where both have there pros and cons one being simple and other being hard to implement.To concluded for me i usually go for armature control as you can control the input current and voltage to the motor also providing a large range of speed in which motor can be operated.
Can I put a variable speed control on any motor?
Well, sort of. I will correct Matthew Lai: steppers, induction motors and synchronous motors all have variable speed controllers these days.The speed of any AC motor is dependent on the applied frequency. However, some AC motors are just not suitable for variable speed operation. Single-phase motors (for reasons I won't go into here. Mostly it has to do with how single-phase motors START. Once they're running, change the frequency, change the speed.) are just not good candidates. There are some tricks you can play (reduce the applied voltage enough, and the motor WILL slow down, but it'll run hotter), but generally single-phase applications are fixed-speed. Three-phase induction motors, synchronous motors, permanent magnet synchronous reluctance and DC excited synchronous designs, are all speed controllable. Very large machines at very slow speeds use Cycloconverter drives. Smaller applications may use Load Commutated Inverters (LCI). Smaller still, standard low-voltage variable frequency drives can now control permanent magnet synchronous motors in addition to induction motors.DC motors are inherently variable speed, dependent on the armature voltage to regulate speed. ("Brushless DC" is a marketing term for "AC induction motor with built-in speed feedback".)Servos and steppers are special cases, but they are also speed controllable. They wouldn't be of much use if they weren't.
Do Diesel Locomotives have a cruise control?
I wish they did! The only form of cruise control our locomotives have is a slow speed control.It is used in hump yard operations to maintain a slow speed when shoving cars over a hump.It is limited to 10 mph.I did have a BNSF unit once that could be set up to 40 mph.Other than that the speed is controlled by the engineer.One poster mentioned a deadman peddle.We don't use those anymore.They are not a form of cruise control though.We have alerters now that require action on the part of the engineer or they will cause a penalty brake application if not reset. EDIT After I answered I received the new Railway Age magazine that has an article you might want to look at.In particular look at the reference to GE's Trip Optimizer which they state is a form of cruise control.http://www.railwayage.com/in-this-issue/...
How can I control the torque/current in a brushless motor? I can control the speed, but I am not interested in it. I would rather set a torque (measured on the shaft) and keep it steady from 0 to 20 rpm.
What you need is a subset of vector control.Sadly, whatever speed controller you have (I presume that what you have is hobby-grade equipment) is unlikely to be of much help. You will have to make your own.You will also need a position encoder for your motor. Sensor-less implementation of vector control do exist, but it is my understanding that they do not work at 0 rpm.A couple of years ago I did more or less what you want to do. I used a STM32F4DISCOVERY module as “brains” of the controller, an AMS Hall encoder for position control and made my own power stage.
What are the applications of speed control of a motor?
Thanks for A2A..There are countless application of speed control…Most important areSpeed control of motors used in traction for controling speed of railwaySpeed control used in liftsVary speed of fan, blower as per requirementSpeed control of small household mixers and big industrial mixers.Speed control of power tools like dreel machine, chapsaw etc.Electric crane, electric vehical, robotics and countless indistrial application….
Is there a way to adjust the playback speed in the YouTube Android app?
Open the YouTube app and pick a video to watch. Tap the three dots button at the top right to bring up the video options menu.From the menu, select the Playback speed option. A second menu with playback speeds will open. Select a speed for video playback. The speeds 1.25x, 1.5x, and 2x will make the video play faster. The 0.75x, 0.5x, and 0.25x speed will slow the video down. Also, 0.25x is slower than 0.75x.