Quad Track: IR-Ball Seeking Crane
This is my LEGO Mindstorms NXT Quad Caterpillar Track Crane, which uses my 'Ultimate Grab' to pick-up and retrieve a Hitechnic Infra-Red Electronic Ball. The Chassis houses 2x NXT Motors to drive the Left and Right pairs of Tracks. A third NXT Motor is used to raise and lower the crane arm. A Small PowerFunctions Motor is used to open and close my Ultimate Crane Claw attachment. The Small PowerFunctions Motor is controlled via a Mindsensors Multiplexer for NXT Motors (NXTMMX-v2). The NXTMMX allows the NXT to control two additional NXT or other LEGO Motors.
The Robot is designed to retrieve a HiTechnic Infrared Electronic Ball (IRB1005). The IRB1005, has four operating modes, and contains 20 infra-red LEDs giving a full signal coverage using pulse modulated mode and is accredited by the RoboCup Jr Technical Committee. The IRB1005 can also be switched to operate in un-modulated (no pulse) mode to be compatible with existing RoboCup Jr requirements. Two additional HiTechnic modes, 1200Hz and 600Hz, provide added flexibility and detection ranges up to 5 meters or more (15+ feet). The pulse modulated IR signals make the HiTechnic Infrared Electronic Ball easier to detect in difficult background lighting conditions.
The HiTechnic Infrared Electronic Ball is detected by using a Hitechnic NXT IRSeeker (NSK1042) which is has a specially designed curved lens and five internal detectors. Tthe IRSeeker has a 240 degree view, making it perfect for playing robot soccer with the HiTechnic IRBall. The IRSeeker has enhanced modes that can detect modulated IR signals, including the new RoboCup J.r stepped modulated mode. It filters out background signals resulting excellent performance in brightly lit rooms and sunny locations. The IRSeeker Sensor returns the signal direction, as well as signal strength, making it easy to locate and gauge the relative distance to the target.
Close-up of the Ultimate Crane Claw Working
An NXT Ultrasonic Sensor is also used to measure the distance to the ball, in order to accurately calculate when the HiTechnic Infrared Electronic Ball is directly under the Crane's Claw. The Signal strength readings from the Hitechnic NXT IRSeeker isn't reliable enough to use on its own for this application.
Quad Caterpillar Track Crane with Claw Open
(The Extra Battery Box supplies power to the Mindsensors NXTMMX)
A limit switch, in the form of a RCX Type Touch Sensor (LEGO Part #879) is used to detect the upper most limit of travel for the Crane's Arm. Initially the Arm is raised until the limit switch is triggered, at that point the NXT Motor is switched off and the Rotation Count for the motor is Zeroed. Further movement of the arm is controlled via Motor Rotation Counts. I prefer the older, and far smaller RCX Type Touch Sensor over the bulky NXT Touch Sensors. They are easier to mount in confined spaces. If I need to use more than a couple RCX Type Touch Sensor, use my home-brew NXT – 8 Input RCX Touch Sensor Mux.
The Claw Motor doesn't have a limit switch, but a Technics Clutch (LEGO Part #60c01) is used instead. The Small PowerFunctions Motor simply runs in one direction to close the claw for a set time period, and the reverse to open the Claw. Should the time period be too long for the claw action, the Technics Clutch simply takes over preventing any gear damage.
A single NXT Motor is used to drive a pair of Track Assemblies for each side. The motor drives the tracks directly. As can be seen from the CAD Model Below the Track Assembly is very simple, and doesn't require any Track Tensioning Mechanism. Each Track assembly can rotate a full 360 degrees with its Technic Type 2 Turntable (Part #48452cx1)mount attached to the main chassis. This allow the vehicle to traverse uneven terrain.
Quad Track: IR-Ball Seeking Crane Instructions:
LEGO Digital Designer Format:
View On-line Instructions:
- Quad Track Crane – Chassis Assembly
- Quad Track Crane – Track Assembly
- Quad Track Crane – Grab Assembly