Designing Hopping Animal and Comic Book Character Toys

A few years ago my husband and I went to Australia for our Wedding anniversary.  In Cairns we saw some really cool wooden toys - kangaroos that hopped down a slanted board.  Awesome!  They looked like an old-fashioned folk toy.  I wish I had bought a hopping kangaroo, but my suitcase was full of stuffed wombats and other furry toys.  I've been meaning to try and make a hopping kangaroo myself, for years, (and more years).  Since I have found Istructables and discovered the joys of making instructables, I thought I'd try my hand at some wood toys.

I found some internet photos of wooden hopping kangaroo toys and worked backwards.  http://www.boranupgallery.com/gifts/small-gift-ideas/lj/hopping-kangaroo/

I played around with some variations and made a working model of a kangaroo toy.  The kangaroo hops really well, with two different legs for a short hop or longer hop. Then I wanted to go a step further and make some other kind of hopping animal toy.... that's when I found out that it is HARD to make even a simple mechanical toy work the way you want it to.   After many rabbit body variations and different leg designs - varying center pivot point, body length, leg height etc... more than a page of trial results later, I have a hopping rabbit version that really hops.  In hindsight, I learned some key factors to consider for the design of hopping toys - mainly, BALANCE and how far you deviate from your prototype design.  Making a duck-bill dinosaur from the kangaroo pattern went a LOT faster than the rabbit - fewer variables to control.

Anyway, here's what I learned, may it help you design your own hopping toys faster and with less effort than I expended. 

Video links for completed toys are in steps 2, 3 and 4

Note: this type of toy has small parts which could pose a CHOKING HAZARD, so not for the under-three-years-old crowd

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

Step 1: Inspiration

I first saw a wooden, hopping, toy Kangaroo when we were in Australia in 2008.  I can't find my pictures from that trip... so I looked on the internet to find some pictures of kangaroo toys.  Here is one.  I'm sorry that I don't know where this came from.. it was a few years ago.  (Please let me know if you know where this came from ... I'd love to attribute the photo).  See this webpage for another example http://www.boranupgallery.com/gifts/small-gift-ideas/lj/hopping-kangaroo/

I kind of sketched the general shape of the pieces, smoothed them out and cut them from wood.  The toy worked pretty well.  I thought the back leg looked too skinny, so I tried a fatter one, which also worked.  The fatter leg produces a 'shorter' hop than the original leg.  

Step 2: 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.
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 friciton, 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.

Here's my hopping kangaroo in action

http://youtu.be/e2o7TjNvUiQ

Step 3: Try a Rabbit and Tweaking the Design

Next step to extend on the concept and try to make another animal toy that can also hop.  How about a rabbit?  My kids like the "Looking for Group" online comic by Ryan Sohmer and Lar Desouza.  (I don't quite get it.)  My younger daughter said that at one point the main character, Richard (some necromancer dude) got shrunk and had to ride around on a rabbit steed (whom he came to love very much).  Pretty wierd, and strange, but kind of an appealing idea - riding around on a bunny.  (for more info, check the Oracle, err, Wikipedia, http://en.wikipedia.org/wiki/Looking_for_Group) . As a joke, I decided to make my daughter a toy 'bunny steed'. 

This step was very time consuming and a bit frustrating... probably because I am not an engineer.  I like 'eyeball' measurements and 'close enough' is good enough for me :-). 

I tried eight rabbit bodies and at least 5 different legs.  I varied pivot points, center of gravity, body shape, leg length etc. etc.   I tried all kinds of combinations and even recorded some of my results.   
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 - 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.

Here's my 'Rabbit Steed' hopping.

http://youtu.be/s1qOY_7xrTs

Step 4: Make a Hopping Dinosaur (Hadrosaur/Duck-billed Dino)

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.

Here is a video of the dinosaur hopping.

http://youtu.be/H2e6Jo0BaOM

I hope you enjoy making your own hopping toys - I think a dragon would be pretty nice :-)