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larm2

arm207a.jpg (3687 bytes)

Completed  arm subassembly. Note the belt drive and reduction gearing.

arm201a.jpg (3950 bytes)

A side view  of the completed base portion of the robot. Note the axle at the top right acting as a range of motion limiter for the model.

arm206a.jpg (4036 bytes)

A close-up of the loading platform and the limit switch that begins the cycle.

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The arm  waits for a can to be loaded onto the loading platform.

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The arm  lifts the can and moves it about 8 inches from the loading platform, then lets it go.

This model was our second attempt at copying an industrial robotic arm using the Lego Mindstorms invention set. The claw portion of the arm can open and close and the arm rotates in one axis above the base. Our concept for this model was that it would be able to lift and carry an empty soda pop can when completed.

We re-used the robotic arm from our first robot arm project. The only change was the mounting method -- the arm would now mount on its side with the claw parallel to the ground instead of perpendicular like our first robot arm.

The next step was to create a base and a loading platform for the arm. We did not make the RCX unit integral to the support base so as to simplify the support base construction. The base is supported by a crossmember at each end that keeps the unit upright. This base was a very stable platform for the arm model to operate on even though it seems rather fragile at first examination.

The motor for swiveling the robotic arm on the base is also reduction geared and has one gear set in addition to being belt driven. We chose belt drive again instead of gearing so as to allow slippage and the ability to grasp a wider range of sizes without worrying about stripped gearing. The two sections are coupled together by the drive axle from the base.

The grasping portion of the arm uses a small connecting piece to limit the range it can open similar to the range of motion limit peg used on the base. We chose this method to simplify the way that the robot uses to determine the home position for the start of a cycle. Again, we could do this because of the slippage of the belt drive system.

There is only one input sensor for this robot. The one contact sensor is located on a portable loading platform. It is designed so be triggered when a soda pop can is placed into the fixture. When the can contacts the limit switch, a complete cycle can begin.

In the pictures you can see a complete cycle. In the fourth picture the robotic arm waits for a can to be loaded on the loading platform. In the fifth picture the can is moved to its new location and the arm can start the entire cycle again.

This model was much easier to build and program that its ancestor (Robotic Arm 1.) The arm base has fewer pieces than the earlier design and was assembled and tested in a short period of time.

Our theory proved correct -- that a much simpler arm base could be created than the one used in Robotic Arm 1. The grip of the claw for this model also seemed to improve since it was used to pick up larger items.


 


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