Tuesday, September 10, 2013

Lego Technic Two Input, Four Output Motor Multiplexers

Motor Multiplexers

I bought the Lego Excavator 42006 a few months ago (for the kids of course) along with the power functions add-on so you could motorize moving the boom up & down along with opening and closing the claw.  The controls are pretty bad though, there are three switches that you have to toggle in just the right combination to get the movement that you want.  It takes me several tries to find the combo I'm looking for, for my 4-year old it is really frustrating.

I also got an EV3 kit recently so I've been working on combining the two so that I end up with a remote-controlled excavator.  I figure that will be much more enjoyable for the kiddos.  The challenge is the EV3 brick only supports 4 motors but I need to be able to control six movements on the excavator.

  • Opening and closing the claw
  • Moving the boom up and down
  • Moving the boom in  and out
  • Rotating the entire platform clockwise and counter clockwise
  • Moving the left track forward and backwards
  • Moving the right track forward and backwards
I need to run both tracks at once in order to move forwards, backwards and steer so that leaves me two motors to control the claw, boom up/down, boom in/out and platform rotation.  I started working on a hardware based motor multiplexer that would let me control four functions from two motors.  

It took me a few iterations to get something compact enough to fit in the excavator.  The turntable mux at the beginning of this video is the one I'm using for the Excavator.  The other two work, they were just too bulky.  The two at the end are a little different in that they will let you enable two outputs at once unlike the turntable mux which only enables one output at a time. Someone else may find them useful though so I included them in the video.

I'm still working on the Excavator but it shouldn't be much longer now that I have the mux figured out.

Build Instructions

Here are the LDD (LEGO Digital Designer) files:


  1. Hi
    Great ideas, will have to try the first one myself.
    What is the white base plate? I have never seen one of those before and would love to get one.
    Regards Glen

  2. Hi Glen, Thanks :) The board is made by a company named minute bot http://www.minutebot.com/minuteproducts/base/