LEGO NXT Rocker-Bogie Suspension
Published on 24 Jun 2007 at 2:59 am.
2 Comments.
Filed under Exploration, Intelligent Systems, Inventions, Lego, NXT, Research, Robotics.
I have just uploaded three videos of a LEGO NXT rover that uses the rocker-bogie suspension system employed by the current Mars rovers. This design is based heavily on the design presented by Brian Bagnall in his book Maximum Lego NXT: Building Robots with Java Brains
I described the rocker-bogie suspension system in a previous post. The idea originated with the bogie, which is a set of six wheels on a train designed in such a way to keep all the wheels on a curved track. The innovation here is to add rockers allowing the wheels to move up and down independently. This enables the rover to handle extremely rough terrain, and as I demonstrate, climb barriers higher than the wheels themselves. A more detailed description can be found on BrickVista Tech-Notes.
The first demo was filmed in my brother’s backyard in Wisconsin where he had just put in a fence. The terrain is relatively rough with bumps and dips with sizes on the order of the diameter of the rover’s wheels.
The second demo was filmed in my office in the Physics Department at the University at Albany. Here the rover climbs a pile of some of my favorite books. Several of the book heights are on the order of the diameter of the wheels themselves. Watch how the rockers allow the wheels to climb independently.
The third demo was filmed in the access road just outside the Physics Department. A small parking barrier, approximately the height of a curb, is the obstacle to be overcome. The rover is able to climb the barrier, and the rocker-bogie suspension allows its wheels to hug the barrier as it rolls over. The rover then heads off towards a small tree… perhaps in search of life.
We improved on the design by increasing the torque on the tires (decreasing the speed) and by replacing the front drive shafts with a gear system. Long LEGO axles tend to take a good deal of torsion and store this energy like a spring. This leads to oscillatory motions in the wheels. In addition, the coupling was too weak to enable our rover to climb the desired obstacles, and our gear system overcomes this. Another way we found to overcome the torsion of long drive shafts is to construct a shaft out of small axles joined by axle connectors.
There are more improvements to be made. One design flaw is that the front wheels are too powerful and sometimes lift the entire front end of the rover without allowing the rockers to rotate. This is because the back wheels are also progressing a given rate of speed and for the rockers to rotate, these wheels would have to slow down. A properly-placed differential should solve this problem.
In the meantime, this basic rover design is sufficiently robust for outdoor exploration.
Below are several books of potential interest.
Kevin Knuth
Albany NY
Gary on 30 Aug 2007 at 1:37 pm: 1
Gee!
It would be nice if you had soon pictures of the bogie system so that we could duplicate it and perhaps work to improve it…
Bender on 7 Jan 2008 at 10:24 am: 2
Nice Work!! Try this one too… without this expensive NXT stuff.. http://de.youtube.com/watch?v=Ub5k5qu7JjY
LowCost with PIC Controller…