How to Choose a Servo
Servos play a very important part in any RC car, with the servo is
responsible for steering the car, and on a nitro cars, a second servo
also controls throttle and braking action. As with any component, there
are different specifications of servos available. So let’s take a look
at what we need to consider when choosing a servo.
Size
Different types and sizes of cars are designed for different size servos, which means that the first thing to take into account is the servo mounting dimensions of your car. The most common size of servo is the “Standard” size. A standard size servo is roughly around 40 mm (length) x 38mm (height) x 20mm (width). These are used on lots of 1/10 and 1/8 vehicles.
A sub-division of standard sized servos are the special “Low-Profile” servos, which is the same length and width as a standard servo, but with a lower height for use in tight spaces. These are commonly used on 1/10 touring cars, some 2WD buggies etc.
Below the standard size servos, there are “Mini”, “Micro”, and even super-small “Sub-Micro” sized servos, which are common on smaller 1/12 and 1/16 size vehicles. Above the standard size servos you find “Large Scale” or “XL” servos, which are much bigger in dimensions, and used for many large scale vehicles in 1/5 and 1/6 sizes.
Torque
The bigger and heavier your RC car is, the higher torque your servo should provide. It is important to choose a servo which is strong enough to handle the size and weight of your car. A normal 1/10 buggy or short course/stadium truck ideally needs a torque of around 10kg. A 1/10 on-road car will be alright with a little less, so around 8kg will be enough. Heavy 4WD trucks need 15kg and upwards, just like most 1/8 and larger vehicles.
Speed
A servo that is fast enough for the type of car is equally important, as a too slow servo will kill the steering feel. The smaller/lighter and faster your car is, the more important it is with a fast servo. On on-road cars you want a servo to be 0,1s or faster, to ensure you have the response needed for these cars. Going to off-road cars, a good 1/10 buggy servo should definitely have a speed of under 0,15s. The heavier the car is, the slower it will be in reaction, so you don’t need the most superfast servos, but the speed should be 0,2s or below for any type of car.
Voltage
Commonly servos run on 6 volts, but if you want to use a 2S LiPo receiver battery without a BEC, you need to choose a 7.4 V compatible servo, of which there are many alternatives available today. These servos can of course also be used with lower voltage, but their performance will be lower. Usually you find torque and speed figures for different voltages in the product information.
Gears
Metal gears will improve the durability of a servo a lot. Metal gear servos recommended for most types of RC cars. For small and light weight cars or other low impact uses, you may choose a plastic gear servo. To save the gears, whether they are plastic or metal, it’s recommended that you use a servo saver. When you buy a quality servo, separate gear sets are available, should you need to replace the gears.
Servo Case
Some servos have full plastic servo cases, while others use a combination of plastic and aluminium, or full aluminium cases. Aluminium is used to improve heat dissipation, but this obviously adds a bit of weight over a plastic case. A full aluminium servo case eliminates flex for a more stable gear train and servo mounting points, which can be useful especially for heavier vehicles. Again, when you buy a quality servo, separate servo cases are available, should you need to replace it.
Motor
Different servos come with different types of electric motors, the most common being: DC, coreless, and brushless. DC motors or the least expensive and best suited to less demanding applications. Coreless motors offer better power and reliability, and change direction more quickly and precisely. Brushless motors produce ultimate power, quicker torque, faster response, greater efficiency and are the longest lasting.
Waterproof
While most servos are fairly well protected, it is only the special waterproof servos that are really made to survive even under water. If you do run a lot in wet conditions, a waterproof servo is the best choice for you.
Output Shaft
Different manufacturers use different servo output shafts, with either 23T, 24T, or 25T spline output shaft used on most small and standard sized servos. Some large scale servos use a larger output axle though, just like some small micro servos use a smaller output shaft. Because of this, it is important to check this what servo arm you have on your car, and if you need a different servo horn. Many cars include different servo horns for different servos.
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