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Zonker's LEGO(*) Articulated Claw

Navigation MenuThis project started out as a challenge to solve a problem for a contest that I couldn't win...

What I mean to say, is that I was too old to enter the contest, but that I was intrigued by the problem, and I sought to build a LEGO solution to meet the challenge. This puzzle was presented to Junior High School and High School students by The Tech Museum of Innovation in San Jose, CA. (Caution: The "Tech" site uses a lot of images, so the main page can take a long time to load!)

The Playing Field:

The Problem: Build a machine that can start within one of the two boundary areas, move to the center, retrieve the object, and deliver the object to the other boundary area.

As I said, I wanted to build a solution using LEGO bricks...

My Answer: The Claw

I wanted to try to overcome the gravity issue. That is, the weight of the battery forcing down, which would be trying to pull many of the LEGO pieces apart!

My decision was to build an articulated claw that could be motorized, and then fashion a device that could support the weight of the motor, claw, and battery while straddling that darned hole!

In hindsight, I could have built something much simpler, lighter and elegant with M-Tron magnets and crane pieces, but I had already picked a challenge, and I got "tunnel vision". I don't know for certain if the object was a battery, with a metal casing, or if it was an object the same size, but made of a non-ferrous material. I presumed it would be a battery.

I started with a battery, and tried to fashion a cradle that could pick up the cell. This proved very difficult, and many of the tested ideas were tossed aside after failing the 'pick-up' test. The battery proved to be a lot heavier than I expected. (Or the LEGOs didn't hold as well as I expected! ;-)

I finally settled on the 1x3 slopped bricks in the pictures. These are still the weakest links, as they are still prone to gravity. I tried to minimize the effect by bracing behind the brick. I minimized the effect of gravity on the supporting legs by layering plates vertically, so that gravity wasn't trying to separate the plates. The 1x3 multi-sided couplers worked the best for joining the feet to the legs.

After I developed a cradle strong enough to hold and pick up the object, I had to develop a method for actually getting the cradle around the battery. I tried a variety of ways, including a fixed cradle that I would have to set down on one end of the object, and then slide it over the object. (I decided that this wouldn't work so well, as I wouldn't have much room to maneuver from a 12" hole, 36" above the object. Try it yourself!)

I finally decided that the cradle would have to open and close around the object, like a fist, or a claw. I began working with the technic gears, and the technic blocks to create a mechanism that would open and close the legs of the cradle. This presented new problems, since this motion would stress the layered plates used for the legs. Gravity would be pushing down on the 1x3 sloped bricks, which would be forcing the legs apart at the bottom. The gearing mechanism would be trying to push the legs together at the top, and the plates were getting stressed.

I never finished adding a motor, because of the added weight. I couldn't find a good way to put the motor on the transport portion, and move the claw legs with simple pressure. (I suppose, thinking about it now, that a simple scissors-type mechanism might have worked, with two motors. One would provide the lift, and the other would open and close the scissor-claw. The weight of the object would have to be enough that it would hold the scissor-claw closed, but not pull it apart.)

More than anything, I present this as a thinking project. It could be a follow-on to a Simple Machines learning module for DACTA classrooms, or to present a problem to think about and try to solve for the puzzle enthusiast among the readers. I'd be interested to hear from students who try to solve this problem by email to freneulo at

These pages are NOT sponsored or endorsed by the LEGO companies.
They are the creation of an enthusiast of LEGO bricks.
The official LEGO home page is
(The LEGO companies have their own pages. This page is mine. :-)

Copyright 1996-99, David K. Z. Harris, N6UOW
Questions? Comments? Additions? Email
frenezulo at

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