General Servos

The following questions are general servo questions.
  • Q. What signal do servos require to operate?

    • A. All Hitec servos require a 3-4V peak to peak square wave pulse. Pulse duration is from 0.9ms to 2.1ms with 1.5ms as center. The pulse refreshes at 50Hz (20ms).

    Servo Pulse Image

  • Q. What is servo deadband?
    • A. Deadband reflects the time it takes for a servo to respond when stick movement is given. Standard servos have a deadband of around 8us and high performance servos have a deadband of 1~3us.
  • Q. What is the input voltage range for my Hitec Servo?
    • A. All Hitec servos can be operated within a 4.8 - 6V (4 or 5 cells) range. Only the HS-50 operates exclusively at 4.8 volts (4 cells). Be aware that "coreless" and digital servos often perform poorly when alkaline batteries are used.
  • Q. What is the meaning of the wire colors?
    • A. On all Hitec servos the black wire is battery ground (negative), the red wire is battery power (positive) and the white or yellow wire is receiver signal.
  • Q. In what direction do stock Hitec servos turn?
    • A. All Hitec servos turn in the clockwise direction (CW).
  • Q. How can I reverse the direction of my analog servo?

    • A. The easiest way to reverse direction is to use the reverse switch in the transmitter. If you have two servos on a y-harness one will have to be modified for reverse rotation or a reversing y-harness used.

    There are four wires that must be switched in order to change the servo direction. Two are on the motor and 2 are on the potentiometer. Switch the red and green wires on the pot and the orange and brown wires on the motor.

    Hitec provides these instructions for information purposes only. Hitec assumes no liability when modifications are made to servos.

    Servo Reverse Diagram

  • Q. What servo should I use for my, car, boat, plane, helicopter, etc.?

    • A. One of the most frequently asked questions is "What servo should I use for.....". While there have been many magazine articles that attempted to provide a general rule of thumb to answer these questions, we offer you the following information.

    There are two factors that go into the design of a servo, Speed and Torque. In many cases, Hitec will create one servo geared for speed while sacrificing some torque, then create its twin, which is geared for torque at the sacrifice of speed. Our 525/545, 625/645, 925/945 servo products are perfect examples.

    If you are not sure which servos to use go with high torque.

    When in doubt ask your peers about servo application questions. Look at what others are using in comparable applications. Usually the kit manufacturer will suggest a servo of a certain physical size and torque value specification in the aircraft, car or boat plans, it's wise to follow their guidelines.

    Even though micro servos like the HS-81 may offer 38oz/in of torque, they are not appropriate for larger powered aircraft due to the flight loads placed on the control surfaces. Smaller servos have thinner gears that are inherently more fragile than those of "standard" sized servos.

     

  • Q. What is the difference between an analog and digital servo?
    • A. The difference is in how the servo motor is controlled via the circuit board (amplifier). The motor of an analog servo receives a signal from the amplifier 30 times a second or at 30Hz. This signal allows the amplifier to update the motor position. Digital servos use a high frequency amplifier that updates the servo motor position 300 times a second or at 300Hz. By updating the motor position more often, the digital servo can deliver full torque from the beginning of movement and increases the holding power of the servo. The quick refresh also allows the digital servo to have a tighter deadband.
  • Q. My older Hitec servo has a white connector, can I use it?
    • A. What you have is a older servo with a Molex connector. Hitec cannot support this product anymore because that type of Molex connector is not manufactured anymore. You can change the plug to a modern Hitec "S" connector using part #57342S.
  • Q. What is the difference between coreless and cored servos?

    • A. In a standard motor like the one in the HS605 servos, there is an iron core between two permanent magnets. Around this core is the wire winding. The core generally has either 3 or 5 sections. As the core moves, these sections cause the core to hesitate slightly when it reaches a different magnetic polarity. This is called ratcheting. Because of this ratcheting, the cored servos have less start up torque and a wider dead band.

    In a coreless servo, there is no iron core. There is one permanent magnet around which is a bell of wire. When electricity is supplied the bell spins around this magnet. Since there are no sections or core, there is no hesitation between poles. This gives the coreless servo better start-up torque and resolution.

     

  • Q. My quarter scale servo came with a y-harness. How do I use it?
    • A. The y-harness is included so you can defeat the Battery Eliminator Circuit of AM receivers. This is required, because that circuit limits the amount of current the servo can draw causing it to behave erratically or lessen its torque. To use the y-harness, plug it into the same channel that you plan on using for your servo. Then plug the switch and battery into one end and the servo into the other end. Do not use a different battery to power the receiver. Because the negative and positive traces in the receiver are linked to each channel, the battery on the y-harness will power the remaining servos and the receiver.
  • Q. Can I use loctite with my Karbonite gears?

    • A. It has come to the attention of the Hitec Product Service Department that some customers owning Hitec's KARBONITE gear servos are using thread locking compounds on the servo horn screws. Thread locking compounds such as the popular LocktiteTM brand, are for use with METAL to METAL fasteners.

    USING A THREAD LOCKING COMPOUND ON KARBONITE GEAR SERVOS WILL CAUSE THE PLASTIC TO FAIL.

    Thread locking compound instructions typically warn against their use on plastics, as most plastic material will become brittle and shatter. If you or any of your friends have used thread locking compounds on plastic / KARBONITE geared servos, please cease using them immediately and contact a Hitec dealer for a replacement gear set.

    Servos