RC Komatsu PC400LC

The RC Komatsu PC400LC is based on an old model which makes it slightly harder to get, I was lucky enough to get one second hand on ebay at a reasonable price. You can tell straight away the quality of this model from how smooth the slewing motion is. The ROS Hitachi model has a lot of friction in the slew motion where as the Joal Komatsu glides around. It is also screwed together slightly better as there is much less plastic in the construction.

It still suffers from the weight issue of the Hitachi, the boom is very heavy but with the new screw mechanism design this should be no problem. The screw mechanisms are based on M3 threaded bar with an N20 gear motor to drive each screw.

Cost Breakdown

Moving the Boom

I decided to mount the motors for the screw mechanism externally on the pivot points of the original fake hydraulic cylinders. This will allow me to modify the design later without having greatly modified the model, with the Hitachi model I cut large holes in the model to accommodate the large servos which ended up rather messy.

N20 gear motors will be used to drive the screw mechanisms due to the large selection of gear ratios and the low power requirements for these motors.

Tack Motors

I’m going to use N20 gear motors for the tracks on this model, there is quite a lot of space below the under carriage of the model so finding space for them should not be a problem. The gears/wheels which drive the model tracks do not have teeth to catch the tracks so I used the 3D printer to create some alternative gears to connect the motors to the tracks. The Hitachi model already had a good gear which meshed with the model tracks making it an easy conversion.

Slewing Mechanism

The slewing mechanism is driven by an N20 gear motor with a electrical slip ring in the centre to allow the electrical connection to pass from the body to the under carriage without getting tangled.

I printed the parts of the slewing mechanism to make sure that everything aligned correctly. The parts need to be strong so that the model doesn’t snap in half and the heavy boom rocks back and forth while the excavator tracks along.


An Arduino pro mini will control the model with four TB6612FNG dual motor drivers controlling the seven motors in the model. There will also be a few LED lights on the model and NRF24 radio module.

RC Komatsu PC400LC Circuit Diagram

RC Komatsu PC400LC YouTube Playlist

RC Komatsu PC400LC Code