RemoteControl

Elcano Remote Control

The Elcano system can run autonomously or by remote control. There have been four systems built for manual or remote control.

Joystick

The first system used an APEM 9000 joystick. The part has five wires: 5V power, ground, and three analog lines. The joystick has two axes. The vertical axis is used for throttle (up) and brakes (down). The third analog signal is the voltage of the joystick when centered. The joystick was used in 2014 and is described in http://www.elcanoproject.org/tutorial/lab2.php. The Low-level code may still contain inputs and processing for an analog joystick.

Bluetooth

In 2015 students built a control system using a Bluetooth receiver to the Arduino. The transmitter was a TI Sitara running Android.

5- and 6-channel RC Controller

The system has been run from either a Hitec Optics 5 2.4 five channel unit or a Spektrum DX6i six channel controller. The Low level circuit board has a3x7 pin socket in the corner to accommodate the receiver. Each channel needs to be on its own interrupt. Since the Arduino Mega has only 6 interrupts and the Arduino Micro has 5, this can be a problem, especially since we want another one or two interrupts to handle the speed. Low level code may still have software to handle these interrupts. The RC controllers send a 1.0 to 2.0 ms pulse on each channel at 30 Hz. Some controllers send these signals in turn. We have built a six-input OR circuit to combine all signals, which would allow processing with just one interrupt. Unfortunately, there is no good way to predict whether the RC unit will send pulses in turn or all at once. In fact, the behavior seems to be determined by the receive unit, not the transmitter. Thus a separate interrupt is required for each channel used. Interrupt processing consists of interrupting on a rising edge, then switching to a falling edge interrupt and logging the pulse width. A width of 1.0 ms typically means one extreme, 1.5 ms is centered, and 2.0 ms is the other extreme., This system can get confusing about which channel is assigned which behavior, and the two controllers assign their channels differently. To go beyond the Arduino interrupt limit, the V2 Low Level board has all RC inputs assigned to Analog Input 8 to 13 of the Arduino. These pins are used digitally. Pins A8-A15 on Arduino Mega, all go to the same port. Thus we can use the pin change interrupt, which is activated whenever any bit of the 8-bit port changes.

Amplitude Shift Keying (ASK) RC Controller

Elcano currently uses a custom-built radio control system with two arduinos, one in the remote control that collects manual inputs and transmits them with a 433MHz ASK radio transmitter, and one on the Elcano vehicle which receives the information sent over radio and converts it into an ElcanoSerial drive packet which is transmitted to C2 over ElcanoSerial. This information is used to manually drive the trike, begin an autonomous routine, or activate the emergency brake and stop the trike.

RC Inputs from the user

The transmitter turn and throttle controls are wired to the transmitter arduino's analog pins, so inputs are initially 10 bits. These are lossily compressed down to 8 bits with a rightward bit shift.

uint16_t turn = analogRead(A1) >> 2;
uint16_t throttle = analogRead(A0) >> 2;

The autonomous and e-brake controls are also wired to analog pins but these values are collected using digitalRead() to directly convert these inputs to a 1 or 0.

uint8_t autoMode = digitalRead(A2);
uint8_t eBrake = digitalRead(A3);

Payload

The transmitter composes these inputs into a 3-byte array:

uint8_t msg[3];
msg[0] = turn & 0xFF;
msg[1] = throttle & 0xFF;
{| cellpadding="5" cellspacing="0" border="1"
|-
|msg[2] = (autoMode || (eBrake << 1)) ; // B000000EA
|}

The RC receiver expects to receive a 3-bytes of data. A valid message contains the autonomous control mode, emergency brake, turn, and throttle data:

inputs[0] = buf[0] ;
inputs[1] = buf[1] ;
inputs[2] = bitRead(buf[2], 0); // auto-mode
inputs[3] = bitRead(buf[2], 1); // ebrake

Later in the code, these values are converted from bytes and Booleans to an ElcanoSerial drive packet. The drive packet has three fields for throttle in cm/s, turn angle in millidegrees, and autonomous and ebrake status transmitted as two consecutive bits, giving a value from 0 (B00) to 3 (B11) but accessible at the bit level using functions such as bitRead().

External Links

[[1]] Details on RH_ASK.h serial frames (the output from the Arduino "transmit" pin)

-- Main.JosephBreithaupt - 2017-10-11

• RC_Tx_elcano_revised.png:
  

<img src="%PUBURLPATH%/%WEB%/%TOPIC%/RC_Tx_elcano_revised.png" alt="RC_Tx_elcano_revised.png" width="878" height="821" />

• rh-ask-frame.png:
  

<img src="%PUBURLPATH%/%WEB%/%TOPIC%/rh-ask-frame.png" alt="rh-ask-frame.png" width="1425" height="246" />