Rough-Terrain Vehicles

First of all, both of the things you see in the picture are missing their NXT Intelligent bricks.  (I'm charging the batteries)

So, I decided to build a Pack-Bot, inspired by projects such as LNE and N-XTreme ATV.  (It's the one on the right)  The idea was that I could use power functions to operate the treads, and have a NXT minibot that came off the front (inspired by this project).  I decided not to attempt this complex undertaking, and I built a simple pack-bot instead.  I'm glad I did.  The gear ratio allowed for good torque and adequate speed, while the front flippers allowed the machine to be lifted over even the largest obstacles.  One of the only problem I ran into was that it could not turn itself back over when flipped onto its back - the front plate rubbed against the ground, and the flippers lacked the torque to "force" the robot back over.  To fix this, I added a single beam projecting upwards directly behind the flipper motor.  This allowed the packbot to like differently on its back, which reduced the load on the flippers.  The other problem is that the treads also slip on their sprokets when the robot is run very hard.  This might just be a result of the LEGO elements, but moving the flippers out one stud and adding a beam to the outside of the central tracks might help.

The thing on left is an exploration of the TECHNIC Unimog parts and pendulum suspension using a turntable.  It is a four wheel drive truck with front wheel wheel steering and rear pendulum suspension.  It is powered off two NXT motors, which power a 3-differential system that powers all four wheels.  This system was inspired by victor28859's projects.  All in all, I am very happy with the Unimog parts.  The 3-stud differentials and universal joints make it easier to make narrower models.  Also, no extra spacing is needed to comply with the TECHNIC system, which is based off of odd numbers.  The portal axles are very rigid and accept different gears.  The rectangular blocks allow for no slippage between the 3-stud differentials and the double bevel gears.  Anyway, this model was reasonably difficult to complete, as I repeatedly dissembled the body structure, continually seeing ways to make it stronger or more compact.  The only gear slippage I encountered in the drive train was between the 16-tooth gear and the 16-tooth differential gear.  I fixed this problem by switching the gear ratios in the portal axles to 3:1, which reduces strain on the drive train under the same load.

Now to see which one is better!

The Mobile Pneumatic Multi Arm Series

So, quite a long time ago, I decided to make a mobile arm.  Too simple?  I also wanted to use pneumatics.  Still simple?  I wanted to get more than three functions out of three motors.  So, MPMA was born.

All in all, it wasn't a bad start to the series.  The drive base was pretty quick, using a white clutch gear to drive forward and turn in reverse off of one motor.  The pneumatic switching mechanism, using a differential and inspired by this project, also worked quite well.  Even the compressor, operating off one RIS motor, worked pretty well.  However, I knew it was possible to drag even more functions out of three motors (MPMA derived 5) and I also toyed with the idea of using more than one motor to move the robot.  And thus was formed MPMA V2...

 MPMA V2 was built around the idea that an output from each of two aforementioned differential "multiplexor" units could drive a tread.  This would give the robot the ability to move forward with the power of two motors.  However, since the treads never rotated backward, MPMA V2 could not be maneuvered in even somewhat tight spaces.  The pumping unit was very slow (though this might have been due to a broken motor) and I never implemented the third pneumatic switch.  The machine's chassis was also weak, adding to the myriad of issues.  Leaning from this, I moved on...

 MPMA V3 was the best robot in the series so far.  It employed a much faster pumping mechanism and a two-jointed arm with a working claw.  The structure was not very strong, but it held together.  MPMA V3 also enjoyed better ground clearance than MPMA V1, and the NXT Intelligent Brick could be easily accessed and removed for battery change.  However, the second joint in the arm did nothing more than move the arm into a more nonfunctional range and was thus rarely used.  Also, the drive base could only go forward and turn in reverse, leading to the next member of the series...

MPMA V4 is probably the best robot in the MPMA series thus far.  Instead of clutch gears and differentials, MPMA uses a mechanical multiplexor custom-built by myself but inspired by this project.  Gaining six outputs from only three motors, MPMA has a fully functional drive base, a single-joint robot arm with working claw on a rotating turntable, and an on-board compressor.  Unlike its predecessors, only two of these functions can operate at the same time (drive base, switches, or rotation/compressor are the combinations) but they are fully functional.  I think that this is a good trade-off.  However, the mechanical multiplexor is prone to slipping the outputs are placed under too much load.  Also, the compressor is slow.

MPMA V4 will hopefully be entered into an unofficial NXT Robotic Arm building challenge.

And, we're done.

Well, I finally finished the programming to an acceptable extent, pictured it, and published it on NXTLog.....here.

Enjoy!