The Bat – Kinetic LEGO Sculpture

Hey everyone, Jason here. Today I am excited to show you Kristal’s latest model which is this kinetic sculpture of a fruit bat also known as a flying fox. So there are four main components to the movement in this model. The first is in the stand which moves the entire model up and down, and the rest have to do with approximating the unique movement of a bat’s wings, which includes flapping them up and down, sweeping them forward on the down stroke and also expanding and contracting them. Let’s start with the stand. The entire motor and drive system is mounted on this floating frame. The motor drives this gray bevel gear which drives two cranks on either side of the frame through this tan gear, and this is what gives us the up, down, forwards, backwards rocking motion. That gray gear also drives this small white gear, which transfers power up through the stand to this gear at the top, which drives all of the movement of the wings in the bat. To explain how the wings work we’re going to walk through all the components of the motion as I add them to this demo model. We’ll start with the simplest component which is flapping of the wings up and down and for that, the wing is just anchored to this axle here so that it can rotate around it. And we have a crank below that is connected to the wings using a liftarm, so that when you rotate the crank, the liftarm acts as a piston to move the wings up and down. In order to sweep the wings forward we’re going to introduce some motion into this axle anchoring the wings so instead of having it rigidly connected to the frame, we’re going to connect it to this pivot so that it can swing back and forth. Now you’ll notice that the liftarm that we’re using to drive the flapping of the wings is now binding because it’s no longer operating in this single plane. So we’re going to replace it with this link which has ball joint sockets on each end so that it can accommodate the new range of motion that we’re introducing. To drive the side-to-side motion we’re going to add another crank, but instead of attaching another piston to this axle at a fixed point, we’re going to put this collar on it which can slide along the axle, and we’re going to attach that collar directly to the crank, so that I rotate the crank, the collar can slide up and down the axle while also moving it from side to side. The last part of the wing motion we want to create is the expansion and contraction of the wings, and for this we are going to drive a simple scissor mechanism in the wings themselves. Here’s a prototype version of the wing to show you how that works. So we need to move the two anchor points of the wing closer together to expand the wing and bring them further apart to contract the wing. Conveniently, that collar we just added, which slides up and down this axle that can be used to do exactly that. We’re going to add this bar in the gap between these two connectors on the collar so that has the collar slides up and down, that bar will as well. Then we’re going to attach the front anchor of the wing here, and the rear anchor of the wing to that bar we just added. Now when we rotate the rear crank the wings expa nded as they sweep forward, and contract as they come back. A ll that’s left to do is to add some gears so that the rear cranks rotate simultaneously with the cranks that the flap the wings, and in this model I have done that. There is a central axle running down the middle with gears coming off the sides to drive the cranks. And that central drive axle is what is driven by this gear at the top of the stand. Put it all together and this is what you get. I also wanted to note that Kristal did a wonderful job decorating the stand. Since these bats only come out in the evening there’s a nice sunset on one side which transitions into twilight on the other, with the moon and some stars. And that is pretty much all there is to it. As always, thanks for watching, keep on building and I’ll see you next time.


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