Melon Factor – Part 1
Part 1 of my NXTLog FoodFactor Competition Entry needed a method to transport models of the large open top pallet type bins used to transport vegetables, such as potatoes, cabbages and pumpkins. I decided on a Forklift Truck to do the job.
Forklift Navigation Details:
The prime purpose of the Forklift Truck is to transport boxes of melons from the delivery depot to the processing plant. The Forklift accomplishes this by using two methods of navigation.
To locate the Melon Boxes, the Forklift uses a 5mW Infra-red LASER. The Melon Boxes have a strip of 'Retro-reflective Tape' on them, which reflects a relatively large proportion of the LASER Light back along the direction from which it came, where it is detected with a Light Sensor.
Once the Forklift has loaded a Melon Box, it next locates a Black Line, which it followers to the Processing Factory. Once at the Factory the Melon Box is unloaded via a Gantry Crane. After the Melons have been emptied from the Melon Box, it is reloaded back onto the Forklift for removal.
NOTE: The LASER shown in the first and third images to the left, are using a 5mW 'Visible' Red Laser Module, unlike the Invisible LASER beam used in this project. The Second image displays some objects I've put the Retro-reflective tape on for LASER Detection. The third image shows the amount of LASER Light 'Reflected Back' to the sensor from 1.2 Mitres.
The LEGO® Mindstorms NXT Forklift Truck shown above is compact, and quick and easy to build. You will need quite a number of extra LEGO® Technic Parts, in order to build it. I suggest you head to BrickLink to purchase the extra Technic parts. The Forklift Truck uses two NXT Motors to dive the Left and right front wheels. The wheels at the rear (show in red in CAD Drawings) are actually Rotacaster® Omni-wheels.
With the Rotacaster® Omni-wheels fitted, the Forklift has a very small turning circle. In fact it can turn in it's own length. The third NXT Motor drives the 2x Thick 'Black' Technic Liftarms (Part #32348), which raise and lower the Forklift's Forks shown at the front. At the end of the 2x Black Technic, Liftarms is the Latching Mechanism that grips hold of the Vegetable Bin, stopping it sliding off the forks during transportation.
Here is the LEGO® Model of the large open top, pallet type bins used to transport vegetables, such as potatoes, cabbages and pumpkins. In this case they are the 'Melon Boxes'. The handle assembly is designed so the container can be lifted via the 'Gantry Crane' without the contents of it falling out.
The complicated appearance of the top of the handle is to allow the container to remain centred at all times when being lifted on the crane's hook. To release the contents of the container, the bottom hinges downward when the bottom rails of the container are the only parts being supported. At other times the bottom is either self supported, or via the handle arrangement.
The black Technic Liftarms on the container's bottom rails allow the tines of the forklift to centre the container prior to lifting it for transportation.
Melon Box Details:
As mentioned above, the Melon Box Bottom's henge to allow the Melons to drop out into the 'Melon Processor Feed Bin'. While building the Melon Boxes, it went through many, many incarnations before I finally got it right.
The handle arrangement caused the most headaches of this part of the 'FoodFactor' build. Having the Melon Box stay on the Forklift without falling off was the first hassle, closely followed by the handles centring arrangement which keeps the Melon Box square to both the Forklift and Gantry Crane's Grabber.
The Forklift took around two hours to complete, but the interface between the bin and both the Forklift and Gantry Crane was many hours. Yep, I missed bed yet again, while trying to solve this LEGO Engineering issue. I wouldn't have slept without it resolved anyway, as I would have been rolling the problem around in the grey matter all night!
NOTE: The CAD Drawings show 4x Technic Part 87083, (Axle 4 with Stop) in the hook centring arrangement. If they are replaced with Technic Part x202, (Pin Long without Friction Ridges Lengthwise), the result removes all the slop from the mechanism.