NXT Crane with Ball Sorting Conveyor System

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This is a LEGO Mindstorms NXT Crane which delivers balls to a Coloured Ball Sorting Conveyor System. The Ball Sorting Conveyor System uses RC Servo Motors to control the Conveyor and Sorting Mechanism. A single NXT Brick Controls 4 standard 180° RC Servos in the Sorting mechanism and another is used for the Crane’s Grab. Two Full-Rotation 360° Servos are used to drive the two conveyor belts. The Servo Motors are controlled via Mindsensors NXTServo Controller module.
LEGO Minstorms NXT Crane with Ball Sorter.
LEGO Mindstorms NXT Crane & Ball Sorting System.

The Crane uses 3x NXT Motors and as mentioned above, a standard RC 180° Servo for the Grab mechanism at the end of the arm. One NXT motor Raises and lowers the Crane’s Arm. A second NXT Motor Rotates the Crave through 180° degrees. The third NXT Motor, allows the Crane to traverse along the track assembly, too and from the Conveyor which loads the Coloured Balls into the Sorter.

Ball Sorting Crane
LEGO Mindstorms NXT Track Crane for Ball Sorting System.

All the functions of this Crane and coloured Ball Sorting Mechanism are controlled by just a single NXT thanks to the Mindsensor NXT-Servo. This  NXT-Servo Controller module effectively gives your NXT another “8 Motor Ports”. In a lot of Robots, the NXT Motors are used as Servos. By using the NXT-Servo and a standard RC Servo you can replace a valuable NXT Motor & NXT Port with this substitute freeing the NXT Components up for another function, to embellish your robot further. Or if you just need a free running motor as part of your robot? Substitute a 360° Full-rotation Servo which can supply hight torque as well.

LEGO Mindstorms NXT Crane & Ball Sorting System Video.

As can be seen from the Video, the NXC Based Software could do with some refining. At this stage, the Crane returns to the Home position each time after delivering a ball to the Conveyor. In the final version this issue will be rectified, along with smoothing out the Cranes rotation as it jerks as it stops. This jerking is due to the direct coupling to the associated NXT Motor. Also the Load Convey and Ball Sorting mechanisms needs to be synchronised with the Crane’s ball deliver. But, as a proof of concept it is working reasonably well……….

RC Servos are Compact and have a very High Torque to weight ratio. If you want to know an easy way to construct the LEGO mounting assembly to suite a standard RC Servo Motor, then check out my article: Technic Mounts for RC type Servos. Mindsensor also sell RC Servo Mounting Kits, with and with out the Motors.

Crane Grab

RC Servos are great for Claws and grabs, due to their compact design. Be aware thate RC Servos are usually “High Torque”, and can bend and brake LEGO Parts! They prove themselves in any application where a precision angle of swing is required. They are also great in pneumatic circuits to Control Pnuematic Valves.

LEGO Mindstorms NXT Controlled Pnuematic Valve Video.

Three standard 180° RC Servo Motors are used as part of the Ball Sorting Mechanism which directs the coloured balls into the appropriate bin according to it’s colour. A Control Arm is attached to each of these RC Servos which direct the oncoming balls to the bins. These Servos travel only 20° in order to connect with the ball and direct it into the appropriate bin.

Ball Sorting Mechanism
LEGO Mindstorms NXT Ball Sorting System Convey & Ball Bins.

A Second 180°RC Servo, pictured with Grey Gears Facing Upwards, is used on the Tower to ensure only one Coloured Ball falls into the Colour Detector well. to avoid jams A Hitechnic Colour Sensor is used as the colour detector. The Servo directly below the 180°RC Servo just mentioned, is a 360° Full-rotation version, which directly drives the Sorting Conveyor. The 360° Full-rotation Servo motors are ideal for this application, with plenty of torque to spare, for this application.

The Conveyor that brings the Balls up to the Sorting Tower, is also a 360° Full-rotation Servo motor. Using these types of Servos is great for saving NXT Motor Ports, provided rotational feedback isn’t required from the motor in your application. They make an excellent replacement for LEGO Power Function Motors.

LEGO Mindstorms NXT Crane Grab Video.

A standard RC servo is designed for 180° swing of the shaft, (90° to left of neutral position, and 90° to right), with ability to position and stop the shaft precisely at any angle in this range. Continuous Rotation servos are a modified version of the RC Servo where the shaft can rotate continuously. On such RC Servos, you can not stop the shaft at precise position.

Lego Technic Servo Mount
LEGO Technics Mounting of RC Servo Motors.

Speed of a 360° Full-rotation Servo can not be controlled precisely, however, up-to 20μS from neutral position, the speed is proportional to the deviation from neutral position, and you can use this fact to control the speed of your 360° Full-rotation servo.

i.e. If your 360° Full-rotation servo has neutral position of 5000μS, you can control it’s speed up-to 5020 μS (clockwise) and 4080μS (anti-clockwise). Beyond this zone, the speed will be constant.

NXT Crane & Ball Sorter
LEGO Mindstorms NXT Crane & Ball Sorting System.

The NXT Crane, the Ball Sorting mechanism, and the Conveyor System, will be part of a lager project involving my LEGO Mindstorms NXT: Line-Following Truck show below. I also envisage an ordering system to select what colour balls and how many are needed. The Ordering System will use Dexter Industries new NXT-Bee Modems to send and acknowledge orders to be delivered by the Truck.

NXT Crane & Ball Sorter
LEGO Mindstorms NXT: Line-Following Truck Fitted with Rotacaster Omni-wheels.
Please visit regularly to view how this project evolves over coming weeks…………

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