Daniel and Joel come to play -

Part 11 - February 2010



The boys, now aged 10 and 12, arrived with their backpacks, full of excitement and ready for a sleepover.   I was ready for them with a brand new Meccano robot which was powered by three stepper motors, limit switches and an electro-magnet through a special interface board linked to the computer USB port.   I wanted to see if they could use the system and program the robot through a set sequence of movements.    


The software written for the system uses a computer screen with icons.  The stepper controller is very easy to use.  You control everything by clicking on the icon buttons; there are no complex programming instructions to learn.   The motor controller tab gives you control over the four possible motors.   Click on a button and the motor turns.  Click on adjacent button, the motor turns in the opposite direction.   Buttons are clickable for direct control for continuous or step motion.  By dragging a slider, the speed can be controlled.     Other tabs control two solid state relay and light emitting diode ports.    It is also possible to record motor positions and LED and relay states.   Each recording of a position is a step in a sequence.   After saving your sequence you can play them back and your model will move automatically through all the recorded steps.  


I wanted to see if the boys could solve the Tower of Hanoi puzzle with the system.  I had three discs all of different sizes.    The puzzle starts with the discs in a neat stack on the left side in ascending order of size, the smallest on top, thus making a conical shape.   The objective of the puzzle is to move the entire stack to a third position through an intermediate position obeying the following rules.

* Only one disc may be moved at a time

* Each move consists of taking the upper disc from one of the positions and placing it on another position, on top of the discs that may already be present. 

* No disc may be placed on a smaller disc.


The robot has three stepper motors.    They moved the shoulder, elbow and base.   Each of these movements was stopped by a limit switch.  The electromagnet on the robot was able to pick up one disc at a time and this also had a limit switch when the magnet touched and pressed on a disc.   The robot had to start from an initial home position before the sequence.  It then moved to the first position above the topmost disc, by moving its shoulder and elbow and base rotation.  This was recorded.   The robot was then instructed to pick up the topmost disc and this was recorded.   The disc was then moved to another position and so forth until the whole puzzle was solved.    They had to not only solve the Tower of Hanoi puzzle but also control the robot.  In the photo, you can see the boys hard at work entering the sequence into the computer.      


Now came the great moment for playback.  After re-stacking the discs on the left, the ‘play’ button was pressed.  The robot then moved to the home position and carried out the sequence of moves all on its own.     The boys and I were overjoyed at this turn of events and we went to celebrate by making pancakes.