Grabber Challenge

Cymraeg

Grabber Retrieval

The Grabber unit
Front aspect of the Grabber unit with the arm in the down and open position. The arm's motor is connected to Port A, the right-hand drive motor is connected to port C, whilst the left to port B. Grabber also has an Infrared sensor connected to port 4 that is situated in the centre of the arm's grabbing mechanism
Front aspect with the arm up and closed to reveal the presence of a touch sensor connected to port 1 (for calibrating the arm mechanism and as a cut off to prevent damage), and a colour sensor aimed at the floor central to the unit.

The Grabber unit has the ability to grab and pick-up objects. The arm is operated by a single motor that first closes, then lifts.

Select the challenge below for the software you are using.

Grabber Challenge using the official Lego Mindstorms Software

The Challenge: The Grabber unit needs to collect a weight and take it to the end point.

Grabber is in the corner of a walled maze. Within the maze is a 'weight' to collect, it is broadcasting on beacon channel 2. Then a blue taped line (with sharp turns) guides the robot through to the end point which is marked with a strip of red tape.
Programming Details

Below are the figures to assist in this challenge for the Grabber unit.

Action Left motor power Right motor power Number of rotations Threshold value
To travel forward one grid square*1 100% 100% 3.8 n/a
90° turn right 25% -25% 1.4 n/a
Wall detection n/a n/a n/a <15
Beacon detection n/a n/a n/a <5

*1 The maze is made on a 5x5 square grid

The Grabber Arm Controls: This is powered by a 'medium motor'. To close and lift the arm you will need to activate this motor at 50% speed for 13 rotations. To lower and open it's 13 rotations at -50% speed.
Do NOT exceed 13 rotations in either direction on the medium motor or you will freeze your program and cause damage to the robot's gear system.


Hint: The grabber unit is easier to steer when the arm is raised, however, to detect the beacon it will need to be in the lowered position, as the IR sensor is part of the lifting arm.


Extension Activity

How would you adapt your program to meet the new challenge given below?

The Grabber unit starts in a different position within the maze. Needs to find and collect the weight (beacon channel 2) then follow a blue line out of the maze. When it reaches the red line end point it needs to drop the weight before negotiating a corridor of right-angled turns in both directions to the exit.

Grabber Challenge using Microsoft MakeCode Software

The Challenge: Grabber need the additional weight to topple the seesaw and allow it to escape.


Programming Details

Below are the figures to assist in this challenge for the Grabber unit.

Action Left motor power Right motor power Number of rotations Threshold value
To travel forward one grid square*1 100% 100% 3.8 n/a
90° turn right 25% -25% 1.4 n/a
Wall detection n/a n/a n/a <15

*1 The maze is made on a 5x5 square grid

The Grabber Arm Controls: This is powered by a 'medium motor'. To close and lift the arm you will need to activate this motor at 50% speed for 13 rotations. To lower and open it's 13 rotations at -50% speed.
Do NOT exceed 13 rotations in either direction on the medium motor or you will freeze your program and cause damage to the robot's gear system.


Hint: The grabber unit is easier to steer when the arm is raised, however, to detect the beacon it will need to be in the lowered position, as the IR sensor is part of the lifting arm.


Extension Activity

How would you adapt your program to meet the new challenge given below?

The Grabber unit starts in a different position within the maze. Needs to find and collect the weight, the route is marked out with a red line. Then it needs to follow a blue line out of the maze. When it reaches the red line end point it needs to drop the weight before negotiating a corridor of right-angled turns in both directions to the exit.

Testing Your Program

Members of the Aberystwyth Robotics Club can share a link to their MakeCode program or send a Lego Mindstorms program directly through the club's Discord server.

Non-members who wish to see if their program works can email nar25@aber.ac.uk either the Lego Mindstorms file or a link to their MakeCode program