A short history of my journey into the art and craft of making ramp walking toys. Also known as passive dynamic walker.
As much as I like making things, enjoy making things that move even more.
It all started with the Ramp Walking Rhino, a design by Robert Lou Ma. I made one, and it kind of worked. I think the problem was a small hinge, which I did not have, so I used a piece of piano hinge instead.
The challenge with these toys is to minimize friction, and the hinge was not sturdy enough to prevent the back leg rubbing on the body.
Tried making a different kind of hinging mechanism, but that ruined the geometry and I lost interest.
Enter the Wombat
No hinges in this one, and I recently bought a scroll saw, so this seemed to be a good pattern to practice on.
It worked pretty well this time, but not being able to leave well enough alone, decided to figure out how and why it worked. If I can observe and describe the action, then I have a better understanding of how it works.
So here goes:
Made a copy in AutoCAD and pin pointed the centre of mass of the body in relation to the pivot point and the centre of mass of the legs, as shown in the image below.
Using movie maker to pause the video and take a screen shot, cropped each frame to remove the background distractions.
On the horizontal, this is the natural resting position. On the ramp, give it a little shove and it starts walking.
The legs have hit the back stop and it is about to tilt forward.
On the front paws, about to tilt just a little more to allow the legs to rotate forward. If the ramp is slightly too steep, it does in fact tilt onto it’s nose. Makes me think the front paws need a little modification.
The legs have come forward, and it is about to tilt backwards.
Tilting backwards and the tail hits the ramp. Starts to slide forward.
Starts all over again – very much the same as frame 2 – The legs have hit the back stop and the tail is lifting off the ramp.
Same as frame 3 – on the front paws and the legs about to swing forward.
And off to see the wizard. If there was a ramp long enough, it would carry on forever, which has given me another idea.
-- Tony, Australia, http://www.wooden-toy-plans.com/