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A FAST NXT2.0 ball sorter (Robot-C)Robot-App Page

Relevant Robots:
  • LEGO - Mindstorms NXT 2.0
Release Date:
App Version:
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Robot App™ Description

A ramp holds the balls to be sorted. Just below is a mechanism with two bars with an alternating movement that let balls go one at a time. The color sensor detects the color of the balls as they go down. According to detected color, two levels of switch points direct the ball to one of 4 buckets.

The ball stream splitter mechanism. When one bar is up, the other is down, so only one ball go through during one cycle. Next to the splitter is the color sensor. The ball channel is shielded to prevent too much ambient light to reach the color sensor. Despite this, sorting reliability decrease with bright lighting. This can be seen in the video at the beginning of slow motion sequence: one yellow ball is incorrectly directed into blue bucket (good video needs good lighting!)

Note that the motors drive the switching levers through a friction pin that may slip at the end of the move. This clutch provides several benefits:
1. Use of unregulated motor control, much faster than slaved modes
2. Simplified (thus faster) program, since it is possible to rotate motors to do the switch, even if it is already positioned.

he sorter uses many angled beams, resulting in weird angles all over the model (modelling it was a challenge, fortunately the relative rotation feature of LeoCAD was a great help!). These angles lead me to use the Technic Axle Joiner Double Flexible to fix the buckets. An added benefit is that you can lift the buckets to retrieve the balls more easily!

use an axle3 with stud and half bushes to secure better the rubber parts.

red balls are first detected as yellow when they are entering field of view of the color sensor. So the color needs to be confirmed after some time (15 ms) when the ball is more centered.

Developer: Philippe (Philo) Hurbain

Installation Instructions

Delivered as:

Attached to the app file


Robot App Requirements



Standard set of LEGO Mindstorms NXT 2.0 #8547
Other requirements:

2hrs. to build the model.

Usage Instructions

Please review the building instructions after clicking the download button.

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