Melon Factor – Part 2    Send article as PDF   
This is Part 2 of my Melon Factor Project, which is part of my NXTLog FoodFactor Competition Entry for May 2012. In Part 1 of my project, for the transportation of the Melons I had them in ‘Bottom Drop’ Boxes. I used a Forklift Truck to transport the boxes of melons from the delivery depot to the processing plant.

The first part of the ‘Processing Plant’ consists of a ‘Gantry Crane’ to take the Melon Boxes from the Forklift, and convey them to the ‘Elevator Bin’. The Melon Box is then placed on the Bin and the Gantry Crane’s Hook is released, which causes the bottom of the Melon Box to henge down, releasing the Melons into the Bin. The Gantry Crane then collects the empty Melon Bin, carrying it back to the waiting ‘Forklift’ where the bin is placed on it’s forks for transport back to the Depot’s ‘Empty Melon Box’ storage area.

Radio Control Type Servo Propulsion:
The ‘Gantry Crane’ and Elevator rely on a number of ‘Radio Control type Servo Motors’ controlled via a ‘Mindsensors Mindstorms NXT, 8 Channel Servo Controller’ (NXTServo-v2).

I fashioned the RC Servo Mounts from LEGO Technic 5×7 Frames. The Lego Frames are attached to the RC Servo motors via ‘Plumbers PVC Pipe Glue’. The whole interface between the Servos and LEGO components is very strong and stable. The output couplings from the RC Servo Shaft to LEGO Components is via gluing LEGO Gears to the standard RC Servo Horns with epoxy. Google: ‘LEGO Mindstorms NXT RC Servo Mounts’ for full details.

Gantry Crane’s Claw:
The Gantry Crane’s Claw is driven by a single Radio Control (RC) type Servo Motor. The Servo drives a simple gear train to both open and close the claw very reliably. Once the Claw grips something and there is power to the Servo it is very difficult to remove the object from it. The LEGO Digital Designer CAD file shows the simplicity of the Claws design.

NOTE: The Claw Mount to the Arms is at 90° to the photographs. The LDD CAD file is Correct.

Gantry Crane’s Lift Arms:
The Gantry Crane’s Lift Arms are controlled via a pair of Radio Control (RC) type Servo Motors, working in parallel to raise the Crane’s Claw. The RC Servos drive a ‘Scissor Lift’ type configuration to move the Crane’s Claw up and down. This choice of mechanism results in very accurate positioning of the claw, as well as increase the load the assembly can control.

Attached either side of the ‘Scissor Lift’ mechanism is a pair of lights. A single light at a time only shines, depending on the direction of the Gantry Crane’s travel. The lights are controlled via a Mindsensors NXT Relay Driver connected to one of the NXT’s ‘Motor Ports’. Depending on the ports output polarity, you can alternate which light is on. The Mindsensors NXT Relay Driver as the name suggest is usually used to drive a relay for switching high current loads.

I came across the Car Interior, 24 SMD LED Light Panel, designed for a 12V vehicle system on eBay for $2.80 each including P&P. In this case the modules are powered via a 11.1v Li-Po battery switched via the Mindsensors NXT Relay Driver.

As can be seen from the photograph below, these LED Lighting Modules deliver a large amount of light for a very small foot print. They are are painful to look directly at. The light is a very clean white and doesn’t appear to affect the colour of the objects is shone on at all. Both photos where taken late at night in a totally dark room, lit only by the modules. I used a F2.0, 50mm Macro lens attached to my Olympus DSLR Camera. The image was taken at F2.0 with no other light source. For more details on the LED Modules, View: ‘Shinning Light for the NXTCam Camera‘.

Gantry Carriage Mechanism:
Gantry Carriage Mechanism is driven via a single Mindstorms NXT Motor. The Gantry Mechanism travels along a twin gear rack rail system. The twin geared rails provides accuracy of travel, as well as stability for the Crane Mechanism.

You need a set of ‘Extra Long’ connecting cables to connect every thing up to the Gantry/Conveyor NTX Brick.

The large Black item with the two thick cables coming out, is a 11.1 volt 220mAh Li-Po rechargeable battery. This battery powers the lighting, and is switched via the Mindsensors NXT Relay Driver. The Parts in ‘Green’ are the Radio Control (RC) Servo Mount Points. And the Parts in Yellow are the ‘Lighting Mounts’.

Details of Gantry Carriage Mechanism:
The Gantry Carriage Mechanism carries the Crane Claw mechanism along the Gantry. The Gantry is 800mm (2’8″) long, and is 600mm (2′) off the ground. With the Claw Arms fully extended the centre of the claw is 160mm (6.6″) off the ground. Which means with the Melon Box on the Forklift with forks raised, the Melon Box’s Handle is in the centre of the Claw.

Conveyor System:
The Feed Bin and Conveyor System take the Melons up to the ‘Washing Mechanism’ for further processing before heading to the ‘Quality Control Area’. The ‘Feed Bin’ is basically a box with part of the bottom and the centre of one side cut out.

The cut-outs allow for the ‘Convey Belt’ to travel through the bin to collect the Melons. The Melons are collected and carried up the conveyor with the help of the ‘Mellon Grab’ shown in the CAD drawing on the right. The ‘Mellon Grab’ is fixed to the conveyor belt, made up of LEGO Track Elements (#57518).

The Conveyor ‘Drive Sprockets’ are 500mm (1’7.5″) apart. The Conveyor has a total of 10 ‘Mellon Grabs’ to transport the Melons to the top, and on to the next processing stage. The conveyor is driven via a ‘Continuous Full-rotation’ Radio Control (RC) type Servo Motor, controlled via a Mindsensors 8 Channel Servo Controller (NXTServo) unit. The Servo drives the Convey Sprocket via a step-down gear train to 12:1 to acquire the correct amount of torque to drive the conveyor.

From the Conveyor, the Melons will feed into the ‘Washer’, prior to being sorted. Once sorted, the quality Melons will be available for-sale, and the rejected Melons are disposed of in an environmental friendly manor, putting even more food on the table. Mean while stay tuned while I get the Software-bugs killed off, and the remaining hardware issues resolved. Which includes extra parts in the post. And only 2 weeks left to get it right!

Gantry Crane Instructions:

Download Instructions: Elevator



Previous Post

Melon Factor - Part 1

Part I 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 ... Read more

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Melon Factor – Part 3

This is Part 3 of my Melon Factor Project, which is part of my NXTLog Food Factor Competition Entry for May 2012. In Part 1 of my project, involved transportation ... Read more

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