NXT Container Crane . A Container Crane from a single NXT set . This is a container crane, made from a single LEGO Mindstorms NXT set, two long axis, rope and a few centimeters garden or aquarium hose.
See the YouTube movie of my NXT Container Crane for action!
It measures 22 centimeters high and 68 centimeters wide, and is designed to grab, lift, lower, and release containers, which are small boxes from IKEA.
The three motors in the NXT set allow for moving in X, Y, and Z directions. However, i had to come up with a mechanism to grab and release the containers...
I started creating the grabber, that exploits gravity and two L shaped levers that clamp and hold the container very well just under the lid. Much later i added the gear wheel and the flipping L for releasing the containers.
The four wheels provide for a stable ride. In order to prevent a skewed ride, i cheated by adding a full-width connection from two long axles. Hence both sides are driven by a single wheel motor. It works without the axles too, however. Another alternative for the axles is to add a circular rope that drives the other side, so in principle it can be build from a single NXT set without extra LEGO parts.
The runner is relatively simple, using some of the grey H-shapes. The runner is connected to a circular rope that runs along the frame and has a few windings around a winch on the runner motor. I pushed aquarium tube over two 8-teeth gear wheels to get a nice cylindrical shape. To prevent slipping the rope has a few windings around the tube.
The lifting rope is stored on a similarly made winch of the third motor. It runs from the winch to the runner, down to the grabber, back up to the runner and to the other side of the frame, where its lose end is fixed to the frame.
The frame was the hardest part. I puzzled most of the remaining parts into it for the widest span without losing stiffness too much. The frame is actually pre-tensioned, in that the bottom side where the runner slides is just slightly hollow.
Than i mounted the NXT brick on top, the cables *just* allowing to connect the motors, failing a long enough cable to connect the US sensor.
Finally i squeezed out a rudimentary cabin from the remaining parts.
I operate the crane with my PC mouse via BlueTooth, using my home-brewn Java application. One REALLY needs to be patient: it is incredibly hard to operate. The motors never run at more than 15% of their speed, and it is next to impossible to control all three at the same time.
Originally, i thought about writing software for so-called zero-swing. This allows modern cranes to hoist/lower and move sideways in one go without ever having incurring a swinging load, hence saving valuable time in emptying eg offloading container vessels. I now believe that this is much too hard without additional input sensors for eg measuring the angles of the lifting rope.
I failed to test how much weight it can lift before taking it apart. It may be assumed to be about a kilogram or so, and believing the rope to be the limiting factor.