Basic Knowledge of Radio Control (RC) Transmitters


Fundamentals of Radio Remote Control

To help friends new to remote control gain a general understanding, this article has been compiled with reference to "Electric Remote Control Model Construction" edited by Mr. Dong Jiongming, published by Taiwan Hualian, and other related materials. Please feel free to point out any inaccuracies.

Remote control, the technology of using high-frequency radio waves to achieve remote operation, originated during World War I. Early control signals were singular, like super-regenerative transceivers, capable of only a single action. This later evolved to superheterodyne and audio-frequency resonant relay types, making multi-channel signal transmission and reception possible. With advancements in electronics, proportional remote control and equipment with more channels emerged. Today, devices with dozens or even hundreds of channels are possible (overseas, equipment with over 20 channels is available; Zhenhua Remote Control also produced 100 units for performance models and robot competitions upon request in 2002). The following briefly introduces some relevant knowledge. To keep it simple, in-depth principles are avoided. Interested readers can refer to books like "Radio Remote Control Technology" published by Electronic Press.


1. Terminology:

① What is Proportional Remote Control?

This means the action's extent (or speed) of the controlled model is proportional to the operator's movement of the transmitter control stick. For example, moving the control stick for the rudder to half its maximum deflection will cause the model boat's or aircraft's rudder to also move to half its maximum angle.

② What is a Channel?

A channel, also known as Ch, simply refers to controlling one related function of the model. For instance, forward and reverse is one channel; left and right steering is one channel; elevator control in aircraft is one channel. It can also control other actions (like turret rotation, elevation, horn, lights, etc.). Importantly, all channels should operate independently and simultaneously without interference.


2. Basic Components of a Remote Control System:

This includes a transmitter (pistol-grip for cars, stick-type for aircraft and boats), a receiver (standard or micro versions), servos (see dedicated articles for classification and details), and electronic speed controllers (ESCs, uni-directional for aircraft, bi-directional or with brakes for cars/boats). Generally, each servo or ESC occupies one channel. Additionally, a power source (batteries) and a switch are required. Batteries are typically rechargeable types like NiCd, NiMH, Lithium, or Li-Polymer. These components together form a complete remote control system.


3. Using Remote Control Equipment in Models:

  1. Basic car and boat models typically use 2 channels. One channel (often left stick) usually controls forward/reverse (and speed with an ESC); the other channel (right stick) controls left/right steering.
  2. Aircraft require 3, 4, 5, or even 6 channels. Fixed-wing aircraft need channels for the horizontal stabilizer (elevator) and ailerons (for rolls and other aerobatics). Helicopters need an additional channel for a gyro, and so on. More channels allow for added fun actions in cars and boats, such as lights, horns, cannons, torpedoes, rockets, water cannons, lifeboat deployment, etc.


4. Key Points to Understand:

Proportional remote control equipment is further classified by signal modulation: Amplitude Modulation (AM), Frequency Modulation (FM), and Pulse Code Modulation (PCM). Their interference resistance varies:

  1. AM has the poorest resistance and is rarely produced now.
  2. FM is more common.
  3. PCM is considered mid-to-high end, offering strong interference resistance. (Example: At a model performance at the Nanjing Zhongshanling Shuixie, interference from a camcorder affected FM-equipped models but not a PCM-equipped one.)

To prevent co-channel interference, specific frequency bands are allocated for model use, similar to radio stations. According to China's Ministry of Information Industry document No. 53 (2003), the frequency points for model remote controls are:

  1. 26MHz–27MHz Band (Surface/Boats): 26.975, 27.125, 26.995 (Brown), 27.145 (Yellow), 27.025, 27.175, 27.045 (Red), 27.195 (Green), 27.075, 27.225, 27.095 (Orange), 27.255 (Blue) – Total 12 points.
  2. 40MHz Band (Surface/Boats): 40.61, 40.69, 40.63, 40.71, 40.65, 40.73, 40.67, 40.75 – Total 8 points.
  3. 40MHz Band (Air): 40.77, 40.79, 40.81, 40.83, 40.85 – Total 5 points.
  4. 72MHz Band (Air): 72.13, 72.79, 72.15, 72.81, 72.17, 72.83, 72.19, 72.85, 72.21, 72.87 – Total 10 points.

A technical specification for transmitters is that the transmission power should be less than 750mW.


5. Application of Radio Remote Control Equipment in Boat Models:

  1. (1) Equipment Selection: Choose based on your needs and budget. "One-step" purchase of a multi-channel, high-end set allows for future expansion. Generally, 2-4 channels are sufficient. For small models, consider equipment with micro receivers and servos. Sailboats require a winch or high-torque servo (also good for larger, powerful models). Standard powerboats can use one ESC and 1-2 standard servos.
  2. ESC Matching: Ensure the ESC matches your motor type (brushed vs. brushless) and its current rating. The ESC's operating current must exceed the motor's maximum current draw to prevent burnout. It's best to test the motor's starting current in the water and choose an ESC with a higher rating (higher current ESCs cost more, but it's safer).
  3. Transmitter Features: If using rechargeable batteries or planning long sessions, check for external power or charging jacks. For aircraft, look for trainer system or simulator ports.
  4. (2) Equipment Installation: Focuses on securely mounting the receiver, servos, and ESC.
  5. Use a mounting plate (same material as the hull for easy bonding) with cutouts for the steering servo. Consider its position relative to the rudder linkage, height, distance, and accessibility for maintenance.
  6. Mount the ESC and receiver using thick double-sided tape or screws, preferably in a higher position in the hull to avoid moisture. Sealing them in a balloon or plastic bag can also provide waterproofing.
  7. Crucial Antenna Handling: Extend the receiver antenna to its full length (related to the receiving frequency). Do not coil or shorten it, as this severely reduces range and sensitivity.
  8. Power Switch: Mount it accessibly, perhaps with a temporary bright sticker during initial runs for easy identification in emergencies.
  9. (3) Pre-Launch Testing and Adjustment: After installation, connect all plugs and insert batteries (observing polarity).
  10. Perform a range check: With the transmitter antenna collapsed, power on the transmitter first, then the receiver. Operate the controls, checking for servo jitter or glitches. The effective range should be 10-15 meters.
  11. Extend the antenna and walk further, checking for normal operation up to 300 meters.
  12. If issues arise, check for nearby interference or same-frequency devices. For motor interference (sparks), solder a 0.01-0.1µF ceramic capacitor across the motor terminals and clean carbon dust from the commutator with alcohol.
  13. After initial testing, proceed to water trials. First, check for leaks and correct trim (longitudinal and lateral balance) to prevent issues or veering. Use the transmitter's trim levers to correct any veering.