Tuesday, January 10, 2012
The finished piece in the emergency waiting room - the ducks have carbon fibre wings, driven by brass cams and rod ends. A negative mold was made for the wings with pottery clay and the feathers were indented with the blade of a table knife. Then a plaster positive followed by a plaster negative into which the fabric and resin was laid down. It would have taken too long for the clay to dry.
The crocodile runs up and down on a linear bearing of my own design. The large central sprocket is part of an idler that gears his cocking mechanism down, and a counterweight made of an old fire extinguisher was also added because the small DC motor only draws a couple amps and couldn't cope with the whole lift. The electronics were designed and built by my son Jim using two 555 timers. When the buttons are pushed it completes a cycle -first it wouldn't go at all because the reed switch position indicator didn't turn back off when the crocodile was at the bottom due to the high gearing so he invented a cheat with small capacitor in series with the logic circuit and a 1 meg resistor across that to bleed it slowly. After a cycle the thing is locked out for two minutes to prevent it being worn out by the younger set.
What I love about steel - it is so light and airy.