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Hello everyone:
I am glad to share this project, the mining excavator, based on Cat 6090.

Phisycal Configuration: The Lego Cat6090 is a motorized digger on tracked wheels, 2 XL motors provided enough torque. On the track frame is placed the main structure, and a heavy duty turntable allows good rotations, without fricctions. The turntable is rotated by means of 1 XL motor. The main structure contains: the XL motor for turntable, the air compressor, 4 servos for pneumatic valves and the controller. The design is ultra compact in order to meet the requierement of size/scale. The tracked whell is ultra rigid structure, designed to resist extreme load.

  • The air compressor has 4 XL motor and 2 pneumatic pumps, in order to provide a constant air flow and high pressure, both pumps are de-phased 180° in order to reduce vibrations.
  • 4 PF-servos open/close 2 way air valves, to command all pneumatic actuators.
  • The boom has 2 large pneumatic actuator. Due to heavy height of the boom, 4 spring supply extra force during the elevation.
  • 2 large pneumatics actuators push/pull the arm, those actuators are placed below the arm.
  • 2 large penumatics actuators dedicate to rotate the bucket.
  • 1 medium pneumatic actuator, open/close the bucket.

Electrical configuration: Three 18650 batteries provide an average of 11.1 V, the compressor are suplied with 11.1 V, and the servos, lights and turntable motor are suplied with 9V. A BMS (Battery Managment System) manages the charge and the discharge durgin the operation. The tracked frame is steering by the use of 11.1 V, and as well is manage by the use of a BMS.

On Board System (OBS):  The name given to the controller. There are two systems, one for the main structure, and the secund is used to move the tracked well. 

  • The main controller, is a server TCP/IP protocol. The controller has a ESP8266 microcontroller with a TCP/IP stack, this controller is able to be programmed in arduino languaje (also micropython) - Teh ESP8266 is used as a sever,
  • Motor driver: used to control the compressor
  • The 4 PF servos are controlled by means of digital outputs, and the lights.
  • ld293d, this is a H-bridge used to control the turntable motor.
  • The second controller, is a ESP8266 as a client, and controls the speed of the tracks. Also, it has a BMS in order to regulates the charges/discharge of the batteries


1) Josyticks: Two joysticks, with 4 dof (degrees of freedom) each of one plus a on/off button, are connected to the server module. 

2) App: An application developmented under Android studio is used to visualizate the air pressure and electrical current, this app is WIP (work in progress). 

Conectivity: The comunication used is socket TCP/IP-

Main features:

  • maximun pressure reached: 52 psi (358 Kpa)
  • Voltage bus: 11.1 V
  • Compressor electrical consuption: 23 W
  • Weight: 6 kg
  • Length: 30 cm width: 20 cm height: 30 cm

Here some pictures, during the construction and commissioning


Note:  my apologies for my primitive english

Edited by diego_ar

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This is very cool! Especially nice to see such a good implementation of pneumatics. Also, spring loading the arm looks like a great solution!

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14 hours ago, NikosSprocket said:

That looks awesome!

What libraries are you using with Andruino to control the PF servos and how do you connect them to the ESP8266?


Hi Nikos: I don't use any particular library to control PF-servos. The PF-servos have 4 wires, 1 Vcc, 1 GND and 2 to control the position of the servo (I attach a link). I use the digital outputs of the ESP8266, the digital outputs dont have enough current and voltage to command the servos (since the servos use 9v and Im not sure but I think 120 ma) the solution us use a Darlington transistors (UNL2803) to put the outputs in 9v.

for example: to move the servo 90°, you need put high (1 V) one command wire and the another put in low (0 V). In arduino the function is bitClear/bitSet to put High or Low.

This info is very usefull


If you need more details, just ask me!!


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