The Bristle-Bot moves because of the flexing of the bristles as the oscillator vibrates. By orienting the bristles in a specific direction, they will exert a force in that direction, causing the Bristle-Bot to move off in the opposite direction.
Most toothbrushes are made of thermoplastic, that becomes soft when heated and re-hardens when cooled. We can exploit this to bend the bristles to the desired angle. You need a large clamp and a kitchen sink.
- Clamp the toothbrush head loosely so that the bristles bend slightly to the rear. Given the next step you might want to ensure that your clamp is liberally oiled to protect it from rusting.
- Try to ensure that they bend evenly as viewed from the front.
- Place into the sink and pour in boiling water until the Bristle-Bot is fully submerged.
- Allow to cool. When you remove the clamp the bristles should remain in their bent position.
The assembly is also a little different to the basic design. Mounting the motor at the front reduces the amount of random motion caused by the motor being at the end of the 'stalk'.
- The motor assembly is constructed as before, by gluing and soldering the (bent) header pins to the motor.
- The battery holder is assembled as before, with a female crimp connector soldered to each terminal.
- Plug the motor header pin directly into one of the battery terminals.
- Construct a connecting cable as before and use this to connect the remaining motor pin to the other battery terminal.
- Attach a blob of Blu-tack to the top of the toothbrush as before and attach the complete motor/battery assembly with the motor to the front.
- Snap in the battery.
The precise direction can be 'trimmed' by adjusting the centre of gravity of the motor/battery assembly. It can be adjusted to make the Bristle-Bot turn to the left or the right, or to move forward in a straight(ish) line.