Komatsu 840 Forwarder



  • Authentic proportions
  • Mechanical crane (not pneumatic)
  • 100 % remote controlled
  • Joystick controlled
  • Strong enough to actully load and carry small logs in the forest

Video at the end of the post.


  • Forward / reverse with 8WD
  • Articulated steering
  • Rotating hitch – Independent tractor and trailer
  • Locking mechanism for rotating hitch
  • Working bogie axes
  • Boom Slew
  • Boom up/down
  • Jib up/down
  • Grapple open/close
  • Grapple rotate
  • Fake 4 cylinder engine


  • Propulsion: 2x PF XL motor connected to a common drive train
  • Steering: Frame steering by two small linear actuators powered by a PF M motor
  • Hitch lock mechanism: Micro motor
    • Slew: Large turntable turned by PF M moto
    • Up/down: LA powered by PF M moto
    • Jib up/down: LA powered by PF M motor
  • Grapple
    • Open/close: Wormgear driven by PF M motor
    • Rotate: Micro motor


  • IMG_6311



    The M motor and the actuators that turns the frame.



    In the compact housing underneath the boom-slew there are two M-motors and two linear actuators and all the gears needed for steering and turning the boom fitted. The drive train is also passing straight through this module.



    No less than nine wires are passing throught the centre of the machine along with the drivetrain. There is actually a total of over 5 meters of wire inside the chassis. The wiring was one of the biggest problems with this project.



    Here is the locking mechanism for the rotating hitch that will lock the tractor and the trailer in purpose of making the crane more stable when loading. How it works in more detail can be seen at http://www.jh-create.com/2012/06/simple-axle-lock-mechanism.html.



    A small module used to provide more stability for the front and also fixating the crankshaft and holding a wire connection.


    The grille and two of the four IR receivers.




    The “patch panel” for powering the four IR receivers.



    The bogie, inspired by DHC6twinotter, became alot more complex that I could ever expected. Factors such as weight, wheel size and not least, articulated steering, put a lot of force on the bogie so it needed to be very stable, but at the same time not to wide in relation to the 14,5 scale. But I am very happy with the final design, although each bogie contains more than a 100 pieces.



    The grapple. It was important for it to be quite strong in order to actually be able to pick up small, but real, logs from the terrain. The grapple is powered by a PF M motor placed in the crane base. By five U-joints the drive train reaches the grapple, without limiting the crane’s movement range and angles. The grapple is rotated by a micro motor turning the turntable. The grapple is attached to the crane in the same way as a real crane making it able to swing in two dimensions.




    The remote control. Joystick design by jjrailton http://www.brickshelf.com/cgi-bin/gallery.cgi?f=301922. The joysticks works exactly as in a real forwarder, greatly improving the maneuverability.



    The drivers’ seat can be turned 360 degrees, the backrest leaning angle can be adjusted as well as the armrests.



    Video below.

  • 6 kommentarer:

    1. I love this model, have you considered to upload it to cuusoo?

      btw, I've linked your blog to mine and featured this creation ^.^

      1. Thank you! I am really flattered by your post :-) I might try cuusoo but I am quite sure it will not get much attention, there are so many good builders out there! :-) By the way, are you familiar with Daniel Martz (avro200 on youtube)? He is one of the very best Technic builders out there and can for sure need some more attention! Check out his channel and also his upcoming project here: http://www.eurobricks.com/forum/index.php?showtopic=64863&st=0

        Best regards,

    2. This blog is quite impressive.The steering is done using two compact linear actuator which is pretty awesome.Can linear actuator be used for rotating purposes.


    3. Thanks! To get a continuous rotating movement from a linear actuator would be hard but maybe not impossible. But to get an axle to rotate a specific set of degrees, less than 180 degrees, would surely be possible.

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    5. Hello,
      really cool model. Did you consider to upload the building instructions on rebrickable.com?
      I think there would be many people who are interested in such a complex machine, especially with its remote Controlled crane.