Category: Container Yard

Automatic LEGO® Container Yard – Post 2: Lifting and moving

Prototype on lifting and moving containers in a container yard

After building the container grabbing mechanism, time has come to move the container around:

The video is shown in double speed.

The lifting mechanism is designed using rack and pinion gears, distributed in four corners, to increase stability. The grabbing mechanism has the rack mounted, and the pinions are mounted on the overhead crane, enclosing the grabbing mechanism, to make it more stable.

Rack enclosed by gears/pinions in four corners. The crossbeams on top of racks are forcing the racks towards the gears.

The reason for having the pinions on the overhead crane, and not on the grabbing mechanism, is simply to make the grabbing mechanism lighter by not having another motor mounted on it.

Another design consideration is to have the same number of gear interfaces from the motor to both sides of the pinion/racks. At my first iteration, the motor was driving one side of the pinions directly, while the motion was directed to the pinions on the other side by gears and shafts. However, since there is some slack in the gears, it introduced a delay in the reaction of pinions on the other side, and the grabbing mechanism was lifted unevenly and wobbly. In the final prototype the motion is first directed to the center, and then directed to the two sides. There is still a slack and delay, but is evenly across the two sides.

Details of the centered motion distribution from motor to gears/pinions

The overhead crane has the weight of the motors evenly split on the two sides, moving as much weight as possible away from the center and reducing the need for reinforcement of the crossbeams.

Simple movement of the overhead crane

The movement in X-direction/crosswise is very simple. A motor, gear and racks in one side, and wheels on the other side, running on a smooth surface. The wheel side has a slight delay in reaction, as it is being “dragged” by the gear/rack side.

To solve this, there would have to be gear/rack on both sides, and the equivalent number (and ratio) of gears between the motor and racks on both sides – same principle as with the grabbing mechanism described above. For now, I decided that the lag on the wheel side is manageable, but I might correct it later, if the crane turns out to be too imprecise.

I experimented with several truss designs for the beams on which the overhead crane is resting on, but I ended up with using the 5×7 liftarms w/ open center, supported by a few other liftarms. This is lighter, but still sturdy.

The next steps will be to create the basis for moving the overhead crane in the X-direction/lengthwise, and introduce some kind of optical recognition/barcode for the containers, so the system can store the information on which containers are stored where.

Automatic LEGO® Container Yard – Post 1: Grabbing the container

First thoughts on an automatic container yard, and a container grab mechanism

As a part of my train layout, I have been thinking about a fully automated container yard – of course controlled by the LEGO® EV3 Mindstorm. My idea: A train comes in, the gantry lifts the container of the wagon, identifies the container, and place it on an empty spot in the container yard.

It sound simple – but it’s really not. The challenges are:

  • XYZ: The gantry must be able to move parallel and perpendicular to the track (X & Y) to move to the right location, and up/down (Z), to place/pickup container from the yard or a wagon.
  • Precise: The mechanism needs to be very precise, else there will be a need for adding many sensors for aligning etc. With millimeter precision, it has to place the container at an exact location, stored this location in a database, and be able to return to that location for picking up – only relying on the XYZ coordinates of the container location.
  • Identifying containers: My initial idea is to identify containers using a color-“barcode”. More about this in another post.
  • Grabbing container: The gantry needs a mechanism to grab a container, with 100% reliability, and without allowing the container to rotate. If the container rotates, it will be nearly impossible to operate without adding active aligning.

I started out by investigating on the grab mechanism. First attempt was to use the linear actuator, and pivoting fingers, like in the LEGO® set 42006. However, this design was a bit too wobbly, and the grab mechanism tended to rotate a bit, due to the axle rotation into the actuator.

The “test container” has a 1×1 Studded Technic Brick in each corner, where the grab mechanism can lock in:

Instead of using the actuator, I tried to go for a design, where hooks in each corner pivots very closely to the container. Additionally, I added some passive guides, to align the grab mechanism into place.

I am very happy with the result! It is much sturdier and very reliable! (I haven’t tested it a 100 times yet though…). See the the video below.