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
Step 3: Try a Rabbit and Tweaking the Design
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.
Step 4: Make a Hopping Dinosaur (Hadrosaur/Duck-billed Dino)
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.
I hope you enjoy making your own hopping toys - I think a dragon would be pretty nice :-)