Solid Holonomic Platform Joiner @120 Degrees

120 Degree Joiner    Send article as PDF   
The Omnidirectional Holonomic Platform more commonly known as the Killough Platform was invented by Stephen Killough and Francois Pin at the Oak Ridge National Laboratories. It uses three specially designed wheel assemblies that can provide force along only one axis (with the rotation of the axle) and can move freely along the direction of the axle. A very detail explanation on Holonomic Platforms can be viewed at TechnicBRICKs blog.

Whilst developing my Omni-Bot I cam up with an extremely Solid Tri-arm Joiner arrangement. Each Arm is separated by 120 Degrees which makes it a great starting point for any 3 Armed project.

120 Degree Joiner

To get started you will need the following Lego Technics Parts:

  • 1 X Technic Tread Sprocket Wheel Large Lego 57519
  • 6 X Black Technic, Pin Long with Friction Ridges Lengthwise Lego 6558
  • 2 X Technic Wedge Belt Wheel (Pulley) Lego 4185
  • 3 X Technic, Pin Connector Perpendicular Long Lego 32557

Using this simple joint you can have a complete Holonomic Platform robot ready to program in under half an hour. Simply replace the wheels shown in the photograph with a set of Rotacaster or other Omni-wheels. You can also use the above joiner as a base for some home-made Omni-wheels.

Technic Omni-Wheels
Technic Constructed Omni-wheel

NOTE: This Omni-wheel is a photograph of an earlier design. If you use the “120 Degree Joiner” design which uses the small Wedge Belt Wheel (Pulley), your wheels will be stronger and track better.

Technic Omni-Wheels
Technic Constructed Omni-wheel


If you replace the Wheels I’ve used on my Omni-wheels with Lego Part #4288 Wheels, which are Full Rubber Balloon types with Technic Axle hole, your Robot will run a lot smother. This is due to the curved profile of these tyres allowing a greater range of contact area with the ground. I’ll have to add some more #4288 Wheels to my want list and test my assumptions with a full-set, rather than a single Omn-wheel using them.

Technic Omni-Wheels
Killough Platform from Above


The easiest way to attach the NXT Programmable Brick to the platform is via a couple of Large Type 2 Technic Turntables (Part 48452cx1). Using these turntables allows for rigid attachment of any 4-sided part/s to the platform including the NXT Brick.

Killough Platform from Below


I’ve found that the Technic Tread Sprocket Wheel to have many more uses than it was originally designed for. Although I would prefer them in Grey or Black, rather than Hot Orange. The Technic Tread Sprocket Wheel is an extremely robust Lego component which should be in everyone’s Technic parts box.

Completed Killough Platform
Completed Killough Platform

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