Deep in a YouTube session one night, I stumbled across some traditional wooden walking toys and immediately added them to my list of potential LEGO projects. After several prototypes and many tweaks I finally finished these cute little guys. A duck and kangaroo that waddle/hop down an incline. The mechanics are extremely simple, and to me they are reminiscent of the escapement on a gravity powered clock, controlling the power of gravity by channeling it into discrete steps.
Instructions are provided below. If they don’t seem to be walking very well there are some hints below for getting them to behave.
They only work on an incline of a specific angle. Too steep and they will get stuck on their front feet, not steep enough and they will get stuck on their back feet. Adjust the incline until you find the sweet spot (note the optimal angle for the duck and kangaroo are slightly different).
There is very little friction between LEGO and cardboard, which is why I’m using felt ramps in the video. I’ve found you can also put a bit of masking tape on the feet give their surface a bit more friction. I’ve tried them on wooden ramps as well with some success. Note that the friction is very important. If the feet slip at all, even a tiny amount, they will lose a lot of energy and not walk as effectively.
For the duck, make sure that the sides of the body aren’t pushed too tightly together. The rear leg needs to be able to swing freely, and if the gap is even a little too tight this won’t be the case. You can just pull the sides apart a bit to make sure the gap is a little wider than the leg. The kangaroo doesn’t have this problem since the legs are on the outside of the body.