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NXT Motor Grader: Part 1: Design

In the coming weeks, I will be making a motor grader based on a MINDSTORMS NXT kit and easilly available LEGO TECHNIC pieces. This is the first part of a five part series - and I will be updating everyone as the model takes shape over the next few weeks.

Today we are going to look at the actual Motor Grader, and see how best to robotize it. This will involve making some compromises as we balance great looks (faithful to the actual vehicle) against NXT functionality and constraints imposed by the TECHNIC pieces.

A new Motor Grader like the caterpillar M series (with joystick control) pictured above are extremely advanced and cost up to half a million dollars with all the attachments and add-on's. The add-ons such as AccuGrade (grade laser that takes away the need for survey stakes you see on road constructions sites) and other electronic kits (GPS, ATS, Cross Slope and Sonic kits) enable the vehicle operator reach perfect grade finish with least number of passes. Motor Graders are also probably the most complex of the construction machines to robotize.

A Motor grader consist of two steerable front wheels (usually powered) and a circle and moldboard (blade) in the middle. A complex arrays of hydraulics controls the blade, the 3D steering and other moving parts.

My initial design plan is to use a mixture of NXT and PF motors and an array of linear actuators ( instead of the hydraulics used in the real thing). A few sensors and NXT-G programs will give the robot some autonomy. So to summarise:
  • 5 motors / 4 linear actuators for the front wheels (providing power, active suspension and 3-d steering)
  • 5 motors / 4 linear actuators in the middle to control the moldboard (providing four degrees of movement for the blade)
  • 1 motor to control the articulations between the front and the back
  • 2 motors / 1 linear acutator to control the rear attachment
  • 4 motors for the rear dfferential drive control / wheels
  • 2 PF battery packs and 2 NXT bricks.
  • 1 IR-Link sensor
With the large amount of electronics and batterypacks you have to address the weight problem. This is a challenge in itself. It looks a bit ambitious - but we will see how it goes in the next few days as the robot start taking shape.

I also want to restrict the extra parts to parts from the currently shipping 2009 TECHNIC models - so that readers can get hold of the parts easilly. This also gives me a chance to play with some new parts introduced with the spring catalog models in the last few months including the ones below I was playing with over the weekend:

The next part will be here tommotow - and it will be on design of the steering control - which is what I am working on right now.

Comments and suggestions are always welcome.

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