TheÂ RC Liebherr A900C Litronic model is based on a Revell plastic model kit which comesÂ disassembled and just snap the pieces together without needing glue. The detail in the model is not to the standard of the diecast Komatsu 400 or Hitachi zaxis 210Â models but the plastic body is much lighter which makes the conversion to radio control easier.
I’m building thisÂ model at the same time asÂ the RC Komatsu PC400LC so there will be a lot of similarity between the two models particularly in the boom control and slewing mechanism.
I’m using screw mechanisms made with N20 gear motors in this model conversionÂ again. I started by usingÂ brass standoffsÂ to make the screw mechanisms however I have since made nicer screw mechanisms for the Komatsu PC400 model so I may make changes to the screw mechanism design before I finish the model.
Slewing Motor and Gears
I plan to use the same method of slewing this excavator as the Komatsu PC400. I’m doing the Komatsu first and it is proving to be a very difficult part of the model.Â It is difficult to couple bothÂ partsÂ of the model together with a hole in the center for the wires without restricting the rotation.
I’m using some plastic gears I got from ebay and driving them with an N20 gear motor to get the rotation. I have a slip ring which I also bought on ebay to stop the wires getting twisted and broken.
I’ve chosen a Tamiya 12 speed gearbox for the drive motor in this model. It’s a flat wideÂ motor which seems to fit the undercarriage of the model well. I chose this motor because I want to find alternatives to the Siku drive motors which are expensive and hard to find. The downside of this motor is that the gears are plastic and so there is a good chance the gears will break when I try to doze something but finding the limits of the motor is the whole point of using it.
The model doesn’t come with a working rack and pinion like the Siku tractors, it just has two solid axles. I’m working on an RC JCB 217S which has a steering rear axle, I will be replacing this with a siku drive motor so I’m going to carefully cut this steering axle from the JCB and use it for the steering on the Liebherr.Â There should be plenty of space to add a steering servo to the under carriage of the model.
Dozer Blade Control
The dozer blade on the Liebherr model uses one of the axles as a pivot point. As IÂ replaced the original axle mountings with the drive motor, I used the drive motor axle as the new pivot point which required a slight widening of the dozer blade arms. The servo to control the blade isÂ locatedÂ on the side of the chasis.
The electronics for this model will most likely be a single 3.3 volt arduino pro mini which will control all the screw mechanism motors, the slew motor and drive motor. It will also control a dozer blade servo and a steering servo. The model will also have a small number of LED work lights.