I grew up with earthmovers and I have operated excavators for many years. My favorite machine is the hydraulic excavator. However, I changed jobs so I don't operate excavators anymore. Unfortunate, because I still regularly get itchy hands when I see these machines running. Unfortunately, buying a real excavator is not an option for me. Now there are remote controlled excavators for sale that run on model-hydraulics, but they cost a fortune. So there was only one thing to do, build one myself!

First i looked on the Internet if there were more people that had this idea. Sure enough, after some searching I found several videos and pictures of working RC excavators that did not cost thousands of dollars.
They were converted excavator models from "Bruder". Yes, childrens toys, but I must say that these models are very detailed. So i bought one and got to work.

Step 1: How It Works

This excavator works with hacked servos, that can spin indefinitely. These servos are connected to wooddrillbit thats running in an aluminum tube, with a steel pin in it which engages in the drill. This makes the turning movement from the servos to a Linair movement for the cylinders.

Step 2: Servo Placement and Controle

You could use the controllers that are in the servo's. There are allot of people that operate the excavator just with the hacked servo's. But i prefer the use of CTI controllers. They just give more smooth and faster movements.
So you have to replace the servo controllers for a CTI controllers.

You will need six hacked servo's in totall. Three for the boom, one for swinging and two for driving the tracks. In the pictures you can see how i placed the servo's in the boom.

You have to reinforce the boom with aluminium plates in serveral places, otherwise it will twist when you are digging.

Step 3: End Circuit for the Boom

I did'nt want the servomotors to burn up when it reached the end of the boommovement. So i made end switches in the boom that stop the servomotors when it reaches the boomstops.
You will need diods and microswitches for this. In the attached drawing you can see the wiring circuit.

Step 4: Swinging

The upperbody of the exavator has to be able to rotate infinite from the undercarriage. I bought slew gears and a jackplug with four contacts. The jackplug is there to feed the trackmotors. Later i saw a better solution for this namely a Slip Ring with Flange(see picture).

Step 5: The Tracks

The tracks are made from plastic but they are reasonably strong. The only thing was that they were a little loose. So i made the drivemotors with sprockets movable so i could adjust the tension of the tracks.

Step 6: Transmitter

I wanted full proportional controle of all the movements all the time. Not that i first had to toggle a switch before i could drive and i wanted a transmitter that was hanging in front off me so i could rest my hands on it. Well i bought two 2.4 Ghz transmitters and receivers. They were cheap ones so when i did something wrong it did'nt cost a fortune. I had a transmitter tray lying around and i built the two transmitters in there.

Step 7: Buckets

I wanted to have more buckets for my excavator so i made some from aluminium. I downloaded some pictures and drawings from internet and started building. I first made some templates from cardboard. See how it fits and then cut them out of aluminium. The buckets are partially welded with aluweld (great stuff!) and coldwelded with JB weld(also great stuff!). I now have three different buckets for my excavator.

Step 8: What You Need

What you need is:
- A model tracked excavator from "Bruder"
-Six metal geared servo's that need to be hacked so they can run indefinitely
-Six CTI motorcontrollers, ore you can use the controllers that are in the servo's
-Six microswitches
-Six diodes
-Two cheap 2.4Ghz transmitters with reseivers if you want to build it yourself, ore you can use what ever transmitter you like. But you will need six channels.
-3 Wooddrillbits
-Slewgears
-Aluminium tubing
-JB weld
-Epoxy
-Paint. I spraypainted the wholemodel in Caterpillarcolors. I wanted my model to look as realas possible. Just go to a Caterpillar dealer and ask for the spraypaint, they will sell you the paint.
-A metallathe is very handy
-Use internet! There are allot of people that are converting these Bruder models. It is very helpfull.
-Allot of patience!!!

Step 9: Building

I have to admit that it was'nt an easy build. It is a little fiddly to get everthing to work properly.
But when it is finished and you are digging dirt in your garden for the first time with your own little RC excavator, it is very satisfying.

This could be the result: video

I have made a blog of this RC conversion. So if you like you can look into my Blog.

Hope you enjoyed it.