DESIGNING HOPPING ANIMAL.pdf

PROYECTO TECNOLOGA 3 ESO

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DESIGNING HOPPING ANIMAL You will need:

* wood 1/2-3/4 inch thick

* optional thin plywood (for legs) - about 1/4 inch thick

* 1/4 inch dowel

* 1/8 inch dowel or bamboo skewer

* 2 washers, center hole a bit larger than 1/4 inch (or axle size).

* scroll saw or hand coping saw

* drill press

* sand paper and files

* paint or other wood surface finish

* wood board, clip board, or book to provide the inclined plane down which the toy hops

Make a Hopping Kangaroo

Use the provided line-drawing pattern or just cut pieces using the sample photo as a pattern.

Cut:

1. Body

2. Two legs

3. Drill holes in legs and body. Lower leg hole and eye should be 1/8 inch holes. Upper leg

hole 1/4 inch to fit pivot axle made from 1/4 inch dowel. Body pivot hole should be greater

than 1/4 inch to allow the leg axle to freely rotate. I drilled 5/16 inch hole.

4. Cut dowels for axle and leg stop - length should be width of body, twice the leg width and a

little extra for the washers.

5. Sand edges smooth, clean up drill holes, sand dowels if needed.


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6. Assemble: Insert dowels into one leg. Add washer to axle (pivot dowel), insert into body,

add the other washer and insert into second leg. Align dowels correctly and press together for

a snug fit. DO NOT GLUE the dowel into the holes until you have tested hopping action.

7. The 1/8 inch dowel on the lower part of the leg should swing freely along the belly until it

hit the 'stops'/bumps by the front leg and tail. These stops constrain the length of the hop

and keep the legs below the body's center of gravity. If the stop is not there, the legs collapse

and you don't get any hops.

8. Use a rough pieces of wood, back of clip board or book to make a ramp, around 25 - 30

degrees slope.

9. Lift kangaroo tail and gently drop, which should start a hopping motion. Vary angle of

slope until the kangaroo hops. If the front leg slips or slides down the slope instead of acting as

a pivot point, use a little bit of masking tape or rubber cement to add some friction, and/or

abrade leg bottom with a file or coarse sand paper.

10. If kangaroo still doesn't hop, see the section on tweaking the design for more suggestions.

Try a Rabbit

After much trial and error, I determined that the pivot point for the leg has to be slightly to the

front of the animal body's center of gravity, NOT exactly centered. If the pivot point for the

leg is slightly in front of the center of gravity, then the animal will have a tendency to fall

forward, exactly what we want for a good hop.

Try to find the center balance point BEFORE you drill your pivot hole. Stick a screw driver

into the pivot hole and the tail end of the critter should tip down lower than the head end. If

your animal won't hop, try these steps:

1. Remove some material from the front of the animal - sand down the nose, front of the ears,

front of the leg (but not the rounded front paw - you need that curve to stabilize the animal for

each forward hop).

2. Add some weight to the back end - tape a penny or washer to the tail and see if you get a

better hop that persists. If this works, consider drilling a few shallow holes near the end of the

tail and glue in some steel ball bearings, fishing weights or metal bbs. (NOTE: DO NOT use

weights if this will be toy for a small child - CHOKING HAZARD)

3. Move the hole forward or backwards as needed. Fill hole with a plug sawn from a dowel -


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sand to fit and pound into place. Grasp body by your forefinger and thumb and try to find the

center of gravity. Drill the hole about 1/8 inch in front of the center of gravity.

4. Make sure the leg can still swing freely.

5. Sometimes the front foot slides down the incline instead of acting as a pivot for the forward

hop. Vary incline angle, add some friction to the paw - a bit of masking tape, rubber, or rough

filing.

6. Optional: Paint design on your rabbit. I used acrylic craft paint and painted a saddle on the

Bunny. Feel free to make a 'regular bunny' too.

Make a Hopping Dinosaur

As one might expect, things get easier with practice...

Making a dinosaur toy was much easier than the rabbit.

First, I did not modifiy the kangaroo pattern very much. I slightly changed shape of head, front

foot and moving leg. Most of the difference is cosmetic, from the painted design and stripes.

I haven't made a pattern drawing, but you can easily make your own dino using the

photographed pieces in the last photo.

Documents

DESIGNING HOPPING ANIMAL.pdf