A Happy Hopping Hippo!
Or you could say he is tap dancing!
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This project uses a Dollar Tree hippo toy (a soft rubber-like toy, sold as 2 animals on a card) and a push-type solenoid. Just like the girl jumping rope animation, a 2.5 V Christmas tree light set flashing bulb pulses the solenoid. The simple hopping action is achieved by having the rear legs loosely anchored to the base, and the solenoid's plunger pushes the figure's front end upward about 1/4 inch off of the base. With the solenoid costing $3.85, and 50 cents for the hippo figure, the project costs about $5. The wall transformer was from an old answering machine.

Here are the parts.

Notice the holes cut in the hippo's rear feet. The opening in the wooden base is roughly carved to accept the solenoid which is glued in place from the underside.

The solenoid is glued with a 5 minute epoxy, and wood blocks provide a stable surface-mountable animation. Papier mache "rocks" will cover the base.

It is just this simple. The hippo's rear feet slip over the screw heads.

The Christmas tree light set flasher bulb pulses the solenoid.

With the 2.5 V bulb in series with the solenoid, and approximately 9 VDC from the wall transformer, the solenoid's coil gets about 7 VDC (6.5 VDC in theory). To preserve the life of the coil and prevent overheating, the solenoid receives only enough voltage to move the figure. Be sure the coil doesn't get too hot to be mounted on wood. It will be used only intermittently.

The hippo on the layout with the elephant bath scene.

More about the project.

After testing the solenoid for many cycles, there is little heat generated in the coil and plunger. It all depends on the actual solenoid, but with the pulsing, the solenoid is only energized a fraction of the time. The optional diode across the solenoid's coil is sometimes called a snubber diode and is beneficial to the circuit. For any motor, light, component, or solenoid, always allow for air to circulate freely around these potentially warm parts. I always like to check these things regularly for signs of heating. If you tend to leave these projects activated unattended, it is best to mount them in metal and keep any warm component away from combustible materials. A timing circuit that limits its use, instead of being constantly moving, will extend the life of the project and avoid over-heating issues.

Having a surface-mounted animation is easier to install and repair, as compared to one that is recessed into the layout's surface. For this project, only a small hole needs to be drilled in the plywood surface. Like with the lions and elephant bath scene, some extra lighting, like footlights, will help greatly.

This project took only minutes to construct and there was little tinkering. The solenoid has what is called a captive plunger and it doesn't need a spring since gravity will return it to the "down" position. It is a "push-type" solenoid meaning that the plunger is pushed away rather than pulled down. For the kangaroo and girl jumping rope animation, the solenoid is a "pull-type" and needs a spring, which was homemade in both projects, perhaps the hardest part was making the spring from scrap wire. With the push-type solenoid, the project is much simpler. In time I will convert the other projects to the push-type if the solenoids wear out.

Instead of papier mache for covering the base and blocks, I might just use real rocks and rock slivers piled up around the base, after painting the bare wood in rock-like colors, a mottled look. Clear Christmas tree lights can be placed among the rocks for up-lighting effects, just like in real landscaping. Just be sure to keep the bare bulbs out of sight. Lichen or other vegetation always helps to achieve a natural look. The craft stores offer many types of artificial foliage. Look for greenery that has very small leaves and cut the smaller sprigs off of the larger bunch for use among the rocks.

The flashing bulb will be placed near the power supply under the layout and positioned for easy changing. I have accumulated many of these bulbs over the years since most light sets supply one or two flashing spares. I have even bought a few cards of these flashing bulbs in different voltage ratings from 2.5, 3.5, 6, 7, and 12 volts. Placing a bit of electrical tape over the bulb will conceal its light and alter the blinking/pulsing cycle. These bulbs will blink differently when cold. Wrapping the bulb with electrical tape will make the bulb retain more warmth. Test several bulbs since they sometimes vary in their blinking, even within a particular voltage range. I use this technique in several places on the layout, even to pulse a relay, and the bulbs are surprisingly robust.

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