Control

The control system of a fighting robot controls and coordinates all the actuators on a robot. It is the interface between the user and the robot, allowing them to make the robot act as intended.

## Considerations

The control system is an interface, hence it will have to convert between the inputs given to it by the user and the output motions. Generally an electrical system is used since the actuators respond to electrical signals. At one end of the system you have the user interface. This interface should be allow the user to control the movement of the robot nimbly and simultaneously operate the robot's weapon to deliver devastating well timed attacks.

The signals from the user interface will then have to reach to the robot. A wireless communication method is generally best for this as a tethered cable is impractical for fighting robots. This communication method needs be fast (low latency) and have adequate range (>10m).

Wireless communication is often prone to interference and attenuation. Hence the protocol used in transmitting the information should factor in these aspects. One particular case is what should happen if the receiver on the robot is not getting any information from the transmitter. One approach is for the receiver's outputs to default to a preset value which stops all actuators. This ensures the robot is safe if the transmitter fails and can no longer control the robot.

Finally the signals received by the receiver will need to be converted to signals that control the actuators. There are two aspects to this. First the information being received needs to be converted into a low-power drive signal. For example if the receiver receives demands for each motor, these numbers need to be be converted into a PWM signal. Secondly in most cases this signal will need to be amplified in order to provide the necessary power to drive the actuators. The circuit you use depends on what type of actuator you are wishing to control, generally it is advised to use a pre-made module such as an ESC to do this.

The system outline above is a generalization of what should be considered when designing a control system. However, its is often more convenient to use an off-the-shelf hobby-grade RC system.

## Hobby-grade RC equipment

When designing a combat robot, the easiest way to set up a control system is to use an off-the-shelf hobby-grade RC system, of the type generally used for model aircraft, quadcopters, boats, cars etc. These consist of a transmitter and a receiver.

### Transmitter

The transmitter is the remote control for the model/robot. The transmitter communicates with the receiver using the radio signals, generally in the 2.4ghz band, although older systems tend to use 27 or 40mhz (the full list of allowed frequencies can be found here). In order to allow two transmitters to be used in the same area the transmitter will usually have a bind procedure which ensures that the signals from one transmitter only affect one receiver. This binding procedure should be included in the transmitter's manual or website.

Each lever and button controls a PWM signal, known as a channel, on the receiver. There are also various other controls which affect how the signals are *mixed* together; on basic transmitters (for example the Turnigy 5x), this is usually limited to "v-tail" or "elevon" mixing. While intended for aircraft, these mixers are useful for controlling the drive motors on differential drive robots, as it allows you to have separate throttle and steering controls. On more advanced transmitters (for example, the Turnigy 9xr), a screen and/or computer interface is available to allow for more advanced mixing and processing techniques, as well as features like model memory, telemetry display etc.

Transmitters come in multiple layouts; the most common is the aircraft-style dual-stick setup, giving you easy continuous control of 4 channels, as well as various other switches and dials. Generally, these sets have one ratcheted axis, intended for the aircraft throttle, which does not return to center; in "mode 1" sets, this is on the right, while "mode 2" puts it on the left. Another common layout is the pistol-grip transmitter (For example the Hobbyking HK-GT2B), often used for surface vehicles such as cars and boats. These are generally 2 channel, with the throttle controlled by a pistol-style trigger, and the steering handled by a wheel mounted on the side of the unit; any further channels are generally in the form of buttons, knobs, and switches. While often limited in channels, this style of controller would be perfectly sufficient for a simple wedge or ramming bot.

### Receiver

The receiver connects to the transmitter through radio waves and outputs signals (generally per-channel PWM) to the servos, ESCs, or other systems. For each channel on the receiver, there are generally 3 connections; Signal (PWM), 5v, and gnd. This means you need at separate 5V supply to power the receiver. Many ESCs include power regulators which can provide this 5V supply (ones that cannot are labeled as *opto or without BEC*)

An exception to this general setup are PPM or SBUS-only receivers, sometimes sold as satellite receivers. These devices output all channel data through a single signal connector. These are generally designed for drones, where all the input signals need to be fed into a flight controller, rather than direct to actuators. If you are planning on running a custom microcontroller-based system within your robot, it might be worth considering one of these receivers as you can program your microcontroller to interpret the complex signals. Using a PPM or SBUS receiver would reduce the number of required pins and simplify the wiring in this scenario.

### ESCs

*Main article: Electronic Speed Controllers (ESCs)*
Electronic Speed Controllers, as the name suggests, control the speed of a motor. They make the motor's speed proportional to the duty cycle of the input square wave from the receiver. They ensure the motor is controlled and protect the rest of the system from the high currents involved in driving electrical motors.

There are many types of ESC for both brushless and brushed DC motors. Some include additional features such as firmware programming to maximize motor performance and opto-isolation on the inputs. As previously mentioned they often also include a BEC which can be used to supply the receiver with 5V.