BlueESC Documentation


The BlueESC is an electronic speed controller for the T100 and T200 Thrusters. It’s custom designed to mount directly to the thrusters and it is waterproof, water-cooled, and pressure-resistant.


When working with electricity, especially in water, always practice caution. Always ensure that connections are secure and watertight. Keep your body away from spinning motors and propellers.

Quick Start

The BlueESC comes preinstalled on the T100 or T200 Thrusters, and you don’t have to do much to get started. All you need is a power source like a 12V battery or power supply and a signal source, like a servo tester, RC radio receiver, or a microcontroller.

  1. Connect the BlueESC to the power source by connecting the thick red and black wires to power and ground (negative).
  2. On the smaller signal cable, connect the black ground wire to the ground wire of the signal source. Connect the red or yellow PWM signal wire to the signal. The BlueESC does not have a battery eliminator circuit (BEC) and cannot power an external device at 5V.
  3. Provide a “stopped” signal at 1500 μs for a few seconds to allow the ESC to initialize. It will beep and the lights will flash briefly.
  4. Once initialized, it’s ready to run!



Specification Table

Voltage 6-22 volts  
Max Current (in water) 35 amps  
Max Current (in air) 25 amps  
Length of Enclosure 18 mm 0.71 in
Diameter of Enclosure 40.4 mm 1.59 in
Cable Length 1 m 39 in
Power Cable Diameter 6.3 mm 0.25 in
Signal Cable Diameter 3.8 mm 0.15 in
Power Cable Colors Red - Positive  
  Black - Negative (Ground)  
Signal Cable Colors Black - Ground  
  Red or Yellow - PWM Signal  
  White - I2C Data (SDA)  
  Green - I2C Clock (SCL)  
Pulse Width Signal    
Signal Voltage 3.3-5 volts  
Update Rate 50-400 Hz  
Stopped 1500 microseconds  
Max forward 1900 microseconds  
Max reverse 1100 microseconds  
Signal Deadband +/- 25 microseconds (centered around 1500 microseconds)  
I2C Signal    
Signal Voltage 5 volts  
I2C Address 0x29 (default) - 0x38  
Maximum Depth To be determined; Designed for 500m+  

3D Model

Coming soon.


LED Indicator Lights

The BlueESC includes two indicator lights that show the status of the ESC. The behavior of these LEDs is consistent with the default behavior in the tgy firmware. Please see the README for tgy for a detailed description of LED indicator light behavior.

I2C Protocol

The I2C communication protocol allows two-directional communication with the ESC. The protocol uses a “register map” allowing registers to be written to and read from.

Throttle Command


The throttle command is a 16-bit signed integer. The sign of the value determines the direction of rotation. Note, you must send a value of “0” at startup to initialize the thruster.

Registers: (0x00-0x01)

  • throttle: (write-only)
    • -32767 (max reverse) to 32767 (max forward)
    • 0 is stopped
    • No deadband


  • Byte 0: throttle_h
  • Byte 1: throttle_l

Data Request


The data registers can be read to provide information on voltage, current, RPM, and temperature. All values are 16-bit unsigned integers.

Registers: (0x02-0x0A)

  • pulse_count: (read-only)
    • Commutation pulses since last request.
    • Calculate rpm with pulse_count/dt*60/motor_pole_count
  • voltage: (read-only)
    • ADC measurement scaled to 16 bits
    • Calculate voltage with voltage/2016
  • temperature: (read-only)
    • ADC measurement scaled to 16 bits
    • Calculate temperature with the Steinhart equation
  • current: (read-only)
    • ADC measurement scaled to 16 bits
    • Calculate current with (current-32767)/891
  • identifier: (read-only)
    • Identifier bit to test if ESC is alive


  • Byte 0: pulse_count_h
  • Byte 1: pulse_count_l
  • Byte 2: voltage_h
  • Byte 3: voltage_l
  • Byte 4: temperature_h
  • Byte 5: temperature_l
  • Byte 6: current_h
  • Byte 7: current_l
  • Byte 8: 0xab (identifier to check if ESC is alive)

Data Conversion

The values sent through I2C for the sensors must be converted to the correct units. The following equations describe how to do so.


The voltage divider uses and 18K and 3.3K resistor for a voltage divider ratio of 6.45. The raw measurement is scaled to 16 bits. The conversion is as follows:

\[\begin{align*} V_{ESC} = 0.0004921 V_{raw} \end{align*}\]

A code example follows:

float voltage() {
  return voltage_raw*0.0004921;


The current is measured by the ACS711, a hall-effect sensor IC. The output is 14.706 A/V with a 2.5V offset. The raw measurements is scaled to 16 bits.

\[\begin{align*} I_{ESC} = 0.001122 (I_{raw}-32767) \end{align*}\]

A code example follows:

float current() {
  (return current_raw-32767)*0.001122;


The temperature is measured by a 10K thermistor (NCP18XH103J03RB) and 3.3K resistor. The temperature is calculated with the Steinhart-Hart equations.

\[\begin{align*} \frac{1}{T}=\frac{1}{T_0}+\frac{1}{B}ln \left (\frac{1}{T}\right ) \end{align*}\]

A code example follows:

// resistance at 25 degrees C
#define THERMISTORNOMINAL 10000      
// temp. for nominal resistance (almost always 25 C)
// The beta coefficient of the thermistor (usually 3000-4000)
#define BCOEFFICIENT 3900
// the value of the 'other' resistor
#define SERIESRESISTOR 3300 

float temperature(_temp_raw) {
  // This code was taken from an Adafruit
  float resistance = SERIESRESISTOR/(65535/float(_temp_raw)-1);

  float steinhart;
  steinhart = resistance / THERMISTORNOMINAL;  // (R/Ro)
  steinhart = log(steinhart);                  // ln(R/Ro)
  steinhart /= BCOEFFICIENT;                   // 1/B * ln(R/Ro)
  steinhart += 1.0 / (TEMPERATURENOMINAL + 273.15); // + (1/To)
  steinhart = 1.0 / steinhart;                 // Invert
  steinhart -= 273.15;                         // convert to C

  return steinhart;


The RPM is sent as pulses since last read, which is the number of commutation cycles since the last time the I2C was polled.

\[\begin{align*} RPS_{ESC} = \frac{RPS_{raw}}{0.5 N_{poles} \Delta t} \end{align*}\] \[\begin{align*} RPM_{ESC} = 60 RPS_{ESC} \end{align*}\]

The value of \(N_{poles}\) depends on the motor. The T100 has 12 poles and the T200 has 14 poles. The RPM measurement does not include direction. You can include direction by adding a negative symbol if the input signal to the ESC is negative.

A code example follows:

float rpm() {  
  _rpm = float(_rpm)/((uint16_t(millis())-_rpmTimer)/1000.0f)*60/float(_poleCount);
  _rpmTimer = millis();

Assigning I2C Addresses

When using more than one ESC, it is necessary to assign unique addresses to each ESC. To assign a new address to the ESC, you will have to update the firmware on the ESC.

Tools Needed:

  1. First, make sure that the ArduinoUSBLinker code is uploaded on your Arduino. You can do this through the Arduino IDE.

  2. Connect the BlueESC signal cable’s black ground wire to one of the “GND” pins on the Arduino. Connect the red or yellow PWM signal wire to Arduino pin 2.

  3. Power the BlueESC with a battery or power supply.

  4. Download the latest BlueESC firmware zip file here. Extract to a convenient location.

  5. There are several ways to upload the firmware to the BlueESC. The first is using avrdude from the command line:

# Navigate to the location containing the BlueESC firmware files
# Replace XX with the desired ID number 0-15 (0 ,1, 2, 3, etc.)
# Replace [programmer port] with serial programmer port, i.e. COM3
avrdude -c stk500v2 -b 19200 -P [programmer port] -p m8 -U flash:w:blueesc_idXX.hex:i

The second method is using a graphical utility such as KKMulticopterTool. Both the 32 and 64 bit versions will work.

  • Set the programmer to ArduinoUSBLinker
  • Select the port with your Arduino.
  • Set the controller to atmega 8-based brushless ESC (8kB flash)
  • Under “Flashing”, click on the “File” tab and browse to the firmware file you wish to flash.
  • Click the green button to flash your BlueESC.

If everything went well, this is the message you should see indicating a successful firmware flash:

Example Code

Arduino with Servo Library

This example uses the Arduino Servo library to control the speed controller. This provides an update rate of 50 Hz and can use any pin on the Arduino board as the “servoPin”.

Note: If you power the Arduino before powering the ESC, then the ESC will miss the initialization step and won’t start. Power them up at the same time, power the ESC first, or press “reset” on the Arduino after applying power to the ESC.

#include <Servo.h>

byte servoPin = 9;
Servo servo;

void setup() {

	servo.writeMicroseconds(1500); // send "stop" signal to ESC.
	delay(1000); // delay to allow the ESC to recognize the stopped signal

void loop() {
	int signal = 1700; // Set signal value, which should be between 1100 and 1900

	servo.writeMicroseconds(signal); // Send signal to ESC.

Arduino with I2C

The following example uses the Blue Robotics Arduino_I2C_ESC library to control the BlueESC through I2C.

#include <Wire.h>
#include "Arduino_I2C_ESC.h"

#define ESC_ADDRESS 0x29

Arduino_I2C_ESC motor(ESC_ADDRESS);

int signal;

void setup() {

void loop() {

  if ( Serial.available() > 0 ) {
    signal = Serial.parseInt();


  Serial.print("ESC: ");
  if(motor.isAlive()) Serial.print("OK\t\t"); 
  else Serial.print("NA\t\t");
  Serial.print(signal);Serial.print(" \t\t");  
  Serial.print(motor.rpm());Serial.print(" RPM\t\t");
  Serial.print(motor.voltage());Serial.print(" V\t\t");
  Serial.print(motor.current());Serial.print(" A\t\t");
  Serial.print(motor.temperature());Serial.print(" `C");

  delay(250); // Update at roughly 4 hz


Firmware Files

The compiled firmware files can be downloaded below. This file includes firmware hex files precompiled with 16 different I2C addresses.

BlueESC Firmware (2015-07-09 a34f109)

Firmware Update and Customization

The Basic ESC uses the tgy firmware which is open source and editable. There are many parameters that can be changed to change the performance of the speed controller.

Firmware Compilation

To compile the firmware, you’ll need the avra AVR Assembler.

Mac: (Uses Homebrew)

brew update
brew install avra
make blueesc.hex

To compile the files with multiple I2C addresses, you can use the following:

make build_blueesc_addresses

Linux (Ubuntu 14 LTS):

sudo apt-get install avra
git clone
cd tgy
make blueesc.hex

Firmware Flashing

The ESC includes a bootloader that allows flashing through the PWM signal wire using a programming like the Turnigy USB Linker or the AfroESC Programmer.

avrdude -c stk500v2 -b 9600 -P [programmer port] -p m8 -U flash:w:bluesc.hex:i