Servo introduction


A Servo is a small device that has an output shaft. This shaft can be positioned to specific angular positions by sending the servo a coded signal. As long as the coded signal exists on the input line, the servo will maintain the angular position of the shaft. As the coded signal changes, the angular position of the shaft changes. In practice, servos are used in radio controlled airplanes to position control surfaces like the elevators and rudders. They are also used in radio controlled cars, puppets, and of course, robots.

So, how does a servo work? The servo motor has some control circuits and a potentiometer (a variable resistor, aka pot) that is connected to the output shaft. In the picture above, the pot can be seen on the right side of the circuit board. This pot allows the control circuitry to monitor the current angle of the servo motor. If the shaft is at the correct angle, then the motor shuts off. If the circuit finds that the angle is not correct, it will turn the motor the correct direction until the angle is correct. The output shaft of the servo is capable of travelling somewhere around 180 degrees. Usually, its somewhere in the 210 degree range, but it varies by manufacturer. A normal servo is used to control an angular motion of between 0 and 180 degrees. A normal servo is mechanically not capable of turning any farther due to a mechanical stop built on to the main output gear.

The amount of power applied to the motor is proportional to the distance it needs to travel. So, if the shaft needs to turn a large distance, the motor will run at full speed. If it needs to turn only a small amount, the motor will run at a slower speed. This is called proportional control.

How do you communicate the angle at which the servo should turn? The control wire is used to communicate the angle. The angle is determined by the duration of a pulse that is applied to the control wire. This is called Pulse Coded Modulation. The servo expects to see a pulse every 20 milliseconds (.02 seconds). The length of the pulse will determine how far the motor turns. A 1.5 millisecond pulse, for example, will make the motor turn to the 90 degree position (often called the neutral position). If the pulse is shorter than 1.5 ms, then the motor will turn the shaft to closer to 0 degress. If the pulse is longer than 1.5ms, the shaft turns closer to 180 degress.

Introduction for the remote:

A radio-controlled model (or RC model) is a model that is steerable with the use of radio control. All types of vehicles imaginable have had RC systems installed in them, including cars, boats, planes, and even helicopters and scale railway locomotives.

History

Radio control has been around since the late 1800s with Nikola Tesla having demonstrated a remote control boat in 1893. The World War II era saw increased development in radio control technology. The Luftwaffe used controllable winged bombs for targeting Allied ships. During the 1950s pioneering work was done by enthusiastic amateurs to create valve based control units. Originally simple 'on-off' systems these evolved to use complex systems of relays to control speed and direction. The information was encoded by varying the signals mark/space ratio (pulse proportional). Rapidly commercial versions of these systems became available. The tuned reed system brought new sophistication, using metal reed switches to resonate with the transmitted signal and operate one of a number of different relays. In the 1960s the availability of transistor based equipment led to the rapid development of fully proportional servo-based systems, again driven largely by amateurs but resulting in commercial products. In the 1980s, integrated circuits made the electronics cheap, small and light enough for multi-channel fully proportional control to become widely available.

In the 1990s miniaturised equipment became widely available, allowing radio control of the smallest models, and by the 2000s radio control was commonplace even for the control of inexpensive toys. At the same time the ingenuity of modellers has been sustained and the achievements of amateur modelers using the latest technology has extended to such subjects as gas-turbine powered aircraft, aerobatic helicopters and submarines, to name but a few examples.

Before the days of radio control many models would use simple burning fuses or clockwork mechanisms to control flight or sailing times. Sometimes clockwork controllers would also control and vary direction or behaviour. Other methods included tethering to a central point (popular for cars and hydroplanes), round the pole control for electric model aircraft and control line (USA: u-control for internal combustion powered aircraft.

Radio-controlled cars use a common set of components for their control and operation. All cars require a transmitter, which has the joysticks for control, or in pistol grip form, a trigger for throttle and a wheel for turning, and a receiver which sits inside the car. The receiver changes the radio signal broadcast from the transmitter into suitable electrical control signals for the other components of the control system. Most radio systems utilize amplitude modulation for the radio signal and encode the control positions with pulse width modulation. Upgraded radio systems are available that use the more robust frequency modulation and pulse code modulation. The radio is wired up to either electronic speed controls or servomechanisms (shortened to "servo" in common usage) which perform actions such as throttle control, braking, steering, and on some cars, engaging either forward or reverse gears. Electronic speed controls and servos are commanded by the receiver through pulse width modulation; pulse duration sets either the amount of current that an electronic speed control allows to flow into the electric motor or sets the angle of the servo. On the models the servo is attached to at least the steering mechanism; rotation of the servo is mechanically changed into a force which steers the wheels on the model, generally through adjustable turnbuckle linkages. Servo savers are integrated into all steering linkages and some nitro throttle linkages. A servo saver is a flexible link between the servo and its linkage that protects the servo's internal gears from damage during impacts or stress.


wikipedia

introduction about our ESC:

An electronic speed control or ESC is a device mounted onboard an electrically powered radio control model in order to vary its drive motor's speed, its direction and even to act as a dynamic brake in certain controllers.

An ESC can be a stand-alone unit which plugs into the receiver's throttle control channel or incorporated into the receiver itself, as is the case in most toy-grade R/C vehicles. Some R/C manufacturers that install proprietary hobby-grade electronics in their entry-level vehicles, vessels or aircraft use onboard electronics that combine the two on a single circuit board.

Regardless of the type used, an ESC interprets control information not as mechanical motion as would be the case of a servo, but rather in a way that varies the switching rate of a network of field effect transistors, or "FET's." The rapid switching of the transistors is what causes the motor itself to emit its characteristic high-pitched whine, especially noticeable at lower speeds. It also allows much smoother and more precise variation of motor speed in a far more efficient manner than the mechanical type with a resistive coil and moving arm once in common use.

Most modern ESCs incorporate a battery eliminator circuit (or BEC) to regulate voltage for the receiver, removing the need for extra batteries. ESCs are normally rated according to maximum current, for example, 25 amperes or 25A. Generally the higher the rating, the larger and heavier the ESC tends to be which is a factor when calculating mass and balance in airplanes. Many modern ESCs support nickel metal hydride and lithium ion polymer batteries with a range of input and cut-off voltages. The type of battery and number of cells connected is an important consideration when choosing a BEC, whether built into the controller or as a stand-alone unit.


ESCs for cars

ESCs designed for sport use in cars generally have reversing capability; newer sport controls can have the reversing ability overridden so that it can be used in a race. Controls designed specifically for racing and even some sport controls have the added advantage of dynamic braking capability. Simply put, the ESC forces the motor to act as a generator by placing an electrical load across the armature. This in turn makes the armature harder to turn, thus slowing or stopping the model. Some controllers add the benefit of regenerative braking. This puts the voltage being generated by the motor back to work recharging the vehicle's drive batteries. On full-sized vehicles, regenerative braking is used in electric and hybrid golf cars and hybrid automobiles while dynamic braking is used in diesel-electric locomotives to help slow trains on long downgrades.


Brushless ESCs

Brushless motors have become very popular with radio controlled airplane hobbyists because of their speed, power, longevity in comparison to traditional motors and light weight. However, brushless DC motor controllers are much more complicated than brushed motor controllers. They have to convert the DC from the battery into phased AC (usually three phase) that the brushless motor can use. The correct phase varies with the motor rotation, which is where the complication lies. Usually, back EMF from the motor is used to detect this rotation, but variations exist that use magnetic or optical detectors. Computer-programmable speed controls generally have user-specified options which allows setting low voltage cut-off limits, timing, acceleration, braking and direction of rotation. Reversing the motor's direction may also be accomplished by switching any two of the three leads from the ESC to the motor.

introduction about brushless motor


A brushless DC motor (BLDC) is an synchronous electric motor that from a modeling perspective looks exactly like a DC motor ( ie linear relationship between current and torque, voltage and rpm). It is a electronically controlled commutation system, instead of a mechanical commutation system (ie brushes )

In a conventional (brushed) DC motor, the brushes make mechanical contact with a set of electrical contacts on the rotor (called the commutator), forming an electrical circuit between the DC electrical source and the armature coil-windings. As the armature rotates on axis, the stationary brushes come into contact with different sections of the rotating commutator. The commutator and brush system form a set of electrical switches, each firing in sequence, such that electrical-power always flows through the armature coil closest to the stationary stator (permanent magnet).

In a BLDC motor, the electromagnets do not move; instead, the permanent magnets rotate and the armature remains static. This gets around the problem of how to transfer current to a moving armature. In order to do this, the brush-system/commutator assembly is replaced by an intelligent electronic controller. The controller performs the same power distribution found in a brushed DC motor, but using a solid-state circuit rather than a commutator/brush system.

BLDC motors offer several advantages over brushed DC motors, including higher efficiency and reliability, reduced noise, longer lifetime (no brush erosion), elimination of ionizing sparks from the commutator, and overall reduction of electromagnetic interference (EMI). The maximum power that can be applied to a BLDC motor is exceptionally high, limited almost exclusively by heat, which can damage the magnets. BLDC's main disadvantage is higher cost, which arises from two issues. First, BLDC motors require complex electronic speed controllers to run. Brushed DC motors can be regulated by a comparatively trivial variable resistor (potentiometer or rheostat), which is inefficient but also satisfactory for cost-sensitive applications. Second, many practical uses have not been well developed in the commercial sector. For example, in the RC hobby scene, even commercial brushless motors are often hand-wound while brushed motors use armature coils which can be inexpensively machine-wound.

BLDC motors are considered to be more efficient than brushed DC motors. This means that for the same input power, a BLDC motor will convert more electrical power into mechanical power than a brushed motor, mostly due to the absence of friction of brushes. The enhanced efficiency is greatest in the no-load and low-load region of the motor's performance curve. Under high mechanical loads, BLDC motors and high-quality brushed motors are comparable in efficiency.

for all those curious about the motor works, i got good explaination on the wikipedia this is the summary:

When a current passes through the coil wound around a soft iron core, the side of the positive pole is acted upon by an upwards force, while the other side is acted upon by a downward force. According to Fleming's left hand rule, the forces cause a turning effect on the coil, making it rotate. To make the motor rotate in a constant direction, "direct current" commutators make the current reverse in direction every half a cycle thus causing the motor to rotate in the same direction.

The problem facing the motor shown above, is when the plane of the coil is parallel to the magnetic field; i.e. the torque is ZERO-when the rotor poles or displaced 90 degree from the stator poles. The motor would not be able to start in this position, but the coil can continue to rotate by inertia.

There is a secondary problem with this simple two-pole design; at the zero-torque position, both commutator brushes are touching across both commutator plates, resulting in a short-circuit that uselessly consumes power without producing any motion. In a low-current battery-powered demonstration this short-circuiting is generally not considered harmful, but if a two-pole motor were designed to do actual work with several hundred watts of power output, this shorting could result in severe commutator overheating, brush damage, and potential welding of the metallic brushes to the commutator.

Unlike the demonstration motor, above, DC motors are commonly designed with more than two poles, are able to start at any position, and do not have any position where current can flow without producing electromotive power.

If the shaft of a DC motor is turned by an external force, the motor will act like a generator and produce an Electromotive force (EMF). During normal operation, the spinning of the motor produces a voltage, known as the counter-EMF (CEMF) or back EMF, because it opposes the applied voltage on the motor. This is the same EMF that is produced when the motor is used as a generator (for example when an electrical load (resistance) is placed across the terminals of the motor and the motor shaft is driven with an external torque). Therefore, the voltage drop across a motor consists of the voltage drop, due to this CEMF, and the parasitic voltage drop resulting from the internal resistance of the armature's windings.As an unloaded DC motor spins, it generates a backwards-flowing electromotive force that resists the current being applied to the motor. The current flow through the motor drops as the rotational speed increases, and a free-spinning motor has very little current flow. It is only when a load is applied to the motor that slows the rotor that the current draw through the motor increases.Apparantly, if the motor had been helped on to run at 261.5 revolutions per minute, the current would have been reduced to zero. In the last result obtained, the current of 5.1 amperes was absorbed in driving the armature against its own friction at the speed of 195 revolutions per minute."
(1917) Hawkins Electrical Guide. Theo. Audel & Co., 359.

here is a good article for changing the motor timing for your drift car.

http://www.misbehavin-rc.com/pit-lane/motor-timing/g-motor-timing.asp

my first drift car, HPI E10 type, with double wishbone steering, shaft drive, bathtub chassy, with disk brake accesories.good handling for beginners, not much of trouble and not too expensive

this is my AE86 body , i made it only for 2 hour including painting and decals

Well, i think it's safer when we drift with a Rc car than the real one, hahahahha, it's inexpensive and have a lot of fun.many top name RC factory already doing mass production for this kind of toys such as:yokomo, tamiya, HPI,and many more
drfit with Rc car is more alike with the real one you should have a lot of skill doing the drift.

There are two ways to start a drift. The first is the clutching technique. When approaching a turn the driver will push in the clutch and shift his car into second gear. Then rev the engine up to around 4000-5000 rpm (it all depends all the model of the car being used) and then slightly turn away from the turn and then cut back towards it hard while at the same time popping the clutch and causing the rear wheels to spin. At this point the drifter has a loss of traction and is beginning to slide around the curve. Now comes the hard part. You have to hold the drift until the next turn. To do this you must keep your foot on the accelerator while at the same time adjusting your car with the steering wheel so you don't spin out. It's not as easy as it sounds. Then as the drifter reaches the end of the turn and approaches the next turn which is in the opposite direction he must cut thewheel in that direction and in some cases, if the previous drift was to slow and they start to regain traction, they must pop the clutch again to get the wheels spinning. And that is how you drift a rear wheel drive car.The second technique is used by a few drifters in rear wheel drives, but is the only way you can really drift a front wheel drive. You have to use the side brake. A front wheel drive can not whip it's tail out because the tires are being driven in the front as opposed to the rear. So when approaching a turn you pull the side brake to cause traction loss. And the rest is pretty much the same except that it's much harder to take more than one turn with a front wheel driver

Basically, drifting is getting your car sideways down a road. It doesn't sound very hard does it? Sounds a lot like power sliding huh? Well it isn't. It's much more complex. Instead of a drifter causing a drift and then countering to straighten out, he will instead over-counter so his car goes into another drift. That is the reason many drifters do it in the mountains, because there are many sharp turns strung together. So in essence a good drifter has the ability to take five or six opposing turns without having traction at any point in time.

this is one of my car , sprint2 chassis with 17x2 motor, fully drift kit

i have 3 drifting car:

cyclone s drift (hpi brand)

E 10 drift (hpi brand)

sprint 2 drift (hpi brand)

all are including the drift kit of:

tyres ( type A )

spring titanium ( competition type )

shocks ( drift )

just buy some lights for the car (brakes lamp and beam lamp)

Do you ever playing an Rc car?not a touring but drift car.......i just play it for the past 4 months and its great, i mean is how we drive is very cool, you goes side ways every turn of the track and it really take alot of effort and skill to do that.well i think i will make this my permanent hobbies.