AI News, Robotics/Components/Actuation Devices/Motors

Robotics/Components/Actuation Devices/Motors

If your priority is to have a fast spinning motor and torque is of little concern a low gearing or even no gearing may be what you need;

however, most motors used in robots need torque over top speed so a motor with a high gear ratio could be more useful.

In a real design the switches can be several different components (Relays, transistors, FETs) or the whole circuit (without the motor) could be an IC (integrated circuit). use

This does not work well, because it will not only reduce the motor's speed, it will also reduce a motor's strength, while also consuming a lot of electricity as large amounts of heat are generated by the resistor.

This pulse needs to be repeated with small intervals (otherwise the servo might turn to a 'save' position or it might simply stay at its current position.

Introduction to Servo Motors

Servo motors (or servos) are self-contained electric devices (see Figure 1 below) that rotate or push parts of a machine with great precision.

In a model car or aircraft, servos move levers back and forth to control steering or adjust wing surfaces.

In 21st-century automobiles, servos manage the car's speed: The gas pedal, similar to the volume control on a radio, sends an electrical signal that tells the car's computer how far down it is pressed.

The car's computer calculates that information and other data from other sensors and sends a signal to the servo attached to the throttle to adjust the engine speed.

You see servo-controlled robots in almost every movie (those complex animatronic puppets have dozens of servos), and you have probably seen a number of robotic animal toys for sale.

These motors run on electricity from a battery and spin at high RPM (rotations per minute) but put out very low torque (a twisting force used to do

(Basic law of physics: work = force x distance.) A tiny electric motor does not have much torque, but it can spin really fast (small force, big distance).

The gear design inside the servo case converts the output to a much slower rotation speed but with more torque (big force, little distance).

On a servo designed to provide more torque for heavier work, the gears are made of metal (see Figure 4 below) and are harder to damage.

It then compares the desired position to the actual position and decides which direction to rotate the shaft so it gets to the desired position.

If she were a simple motor in a robot arm and you were the microprocessor, you would have to spend some of your time watching what she did and giving her commands to move her back to the right spot (this is called a feedback loop).

A pulse is a transition from low voltage to high voltage which stays high for a short time, and then returns to low.

Have you ever picked up one end of a rope that was tied to a tree or held one end of a jump rope while a friend held the other?

As you raise your hand up and down, if you keep your hand in the air longer, someone watching this experiment from the side would see that the pulse in the rope would be longer or wider.

If you keep your end going up and down, making a whole bunch of these pulses one after another, you have created a pulse train (see Figure 6 below).

A system that passes information based on the width of pulses uses pulse width modulation (or PWM) and is a very common way of controlling motor speeds and LED brightness as well as servo motor position.

Complete Motor Guide for Robotics

Brushless DC (BLDC) motors are called by many names: brushless permanent magnet, permanent magnet ac motors, permanent magnet synchronous motors etc.

Then the construction of a brushless DC motor is very similar to the AC motor making it a true synchronous motor but one disadvantage is that it is more expensive than an equivalent “brushed” motor design.

Control The control of the brushless DC motors is very different from the normal brushed DC motor, in that it this type of motor incorporates some means to detect the rotors angular position (or magnetic poles) required to produce the feedback signals required to control the semiconductor switching devices.

Brushless DC motors can be constructed to have, an external permanent magnet rotor and an internal electromagnet stator or an internal permanent magnet rotor and an external electromagnet stator.

This shifting of the magnetic field in the stator produces torque because of the development of repulsion (Red winding – NORTH-NORTH alignment) and attraction forces (BLUE winding – NORTH-SOUTH alignment), which moves the rotor in the clockwise direction.

Brushless ESC systems basically create a tri-phase AC power output of limited voltage from an onboard DC power input, to run brushless motors by sending a sequence of AC signals generated from the ESC's circuitry, employing a very low impedance for rotation.

Brushless motors, otherwise called outrunners or inrunners depending on their physical configuration, have become very popular with 'electroflight' radio-control aeromodeling hobbyists because of their efficiency, power, longevity and light weight in comparison to traditional brushed motors.

The correct phase varies with the motor rotation, which is to be taken into account by the ESC: Usually, back EMF from the motor is used to detect this rotation, but variations exist that use magnetic (Hall Effect) or optical detectors.

Computer-programmable speed controls generally have user-specified options which allow setting low voltage cut-off limits, timing, acceleration, braking and direction of rotation.

You shouldn’t connect a high voltage battery to a low voltage ESC, but it is also wasteful to use a high voltage ESC with a low voltage battery.

Advantages of the Brushless DC Motor compared to its “brushed” cousin is higher efficiencies, high reliability, low electrical noise, good speed control and more importantly, no brushes or commutator to wear out producing a much higher speed.

1ms will reduce its speed to minimum or even stop it (it depend upon the ESC model) while a 2ms pulse will run the motor on its fullest speed.

Sometimes ESC needs calibration and in terms of ESCs, calibration means to set the max and min speeds of the motor in relation to the max and min width of the PWM signal sent by the Arduino.

The default signal range for most servo motors and ESCs is a high signal width between 1000 and 2000 microseconds over a repetition period of 20 milliseconds (assuming a 50hz PWM signal).

To this end, we calibrated the ESCs to read a signal width from 700 to 2000 microseconds with 700 being the stop speed and 2000 being the max speed.

To enter programming mode, the maximum servo signal (2000 microseconds) is sent to the ESC, the ESC is powered on and waits for two seconds, then the minimum servo signal is sent (700 microseconds).

Once the ESC emits a series of confirmation beeps (special wave signals sent to the motor to emit beeping sounds), the ESC is calibrated (check the ESC specific datasheet for details).

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