- 1 laptop with Crumble software installed
- 1 Crumble controller & 2 Crumble-friendly switches
- 1 Crumble-friendly battery box; 3 AA batteries
- A pair of motors (with croc-leads attached) & wheels
- 4 long & 2 short croc-leads and a micro-USB cable
- 2 K’nex wheels and an axle.
- An egg box
The construction of the buggy is ridiculously simple: we pushed the axles of the motors through the sides of an egg box lid, as close to one end as possible, then attached the wheels. For the front wheels we pushed a K’nex axle through he other end of the box and attached a pair of similar sized wheels. (Lego technic would also work fine.) The Crumble and battery box then sit inside the buggy.
The motors are connected to the Crumble’s motor outputs (the bottom two pads on either side of the Crumble). Note that to get the wheels to turn in the same direction and move the buggy forwards, the motors actually need to turn in opposite directions (as they are arranged back-to-back). This can be achieved in software, by setting one to “forwards” and one to “reverse” or, as shown here, by connecting one motor in the conventional way (red wire to the positive pad; black wire to the negative) and the other motor reversed (red wire to the negative pad).
One of the switches was connected between the second positive output of the battery pack and “input A” on the Crumble (the yellow croc leads). The other switch was connected between the Crumble’s “power out” (top right) pad and input D (the green croc leads). The battery pack is connected to the Crumble in the usual way.
The Crumble program is shown below. If both switches are pressed (“A is Hi” and “B is Hi”), both motors operate and the buggy moves forwards. If only one switch is pressed, only the motor on that side of the buggy runs and the buggy turns. The green and yellow croc leads are long enough that our 3yr-old can walk behind the buggy and use the buttons to steer it.
NOTE: The motor power is set to only 25%. This ensures that the buggy moves at a slow walking pace but it can also help to reduce glitches (e.g. the motor LEDs on the Crumble flicker, but the spindles don’t turn) due to interference being picked up by the long leads to the switches.