Go-Rilla- Micro-scout based COG shifting biped


I was contacted by Syngress Publishing because they wanted to make a step by step construction for the Dark Side Developer Kit. This is the final biped I made for the book: LEGO Mindstorms: Dark Side Robots, Creatures, and Transports. 

Complete building instruction can be found in the book. 

After having built my DSDK AT-ST and Super Battle Droid and struggling to get them to walk without falling over, I came up with Go-Rilla. On AT-ST, the center of gravity is far away from the center of rotation for side to side leaning. If I keep the rotation rate slow enough and the amount of lean small enough, DSDK AT-ST walks, but more slowly than I'd like. As I watched it swing side to side, it made me think of a mechanical metronome that keeps time for musicians.

The metronome uses a spring to swing a beam back and forth. One end of the beam is free, and the other end is attached to the metronome. There is mass on the spring that affects how quickly the beam can swing back and forth. With the mass at the far end of the beam, the metronome goes very slowly. With the mass closest to the metronome, the metronome goes very quickly. 

In the case of DSDK AT-ST, the mass (the microscout's batteries) is far away from the rotation point. I realized that this meant I needed gear down the drive mechanism to make the side to side oscillation's speed match the natural mechanical oscillation speed of DADK AT-ST.

I realized that if I used AT-ST's leg design, but hung the Micro-scout down from the hips, the center of gravity would be much closer to the center of rotation. At about the same time, I figured out how to make an extremely compact drive train using only five gears. After trying different gear ratios, I was able to find the ratio that best matched the natural oscillation frequency of Go-Rilla.

Go-Rilla is a weight shifter, but I also think of him as an angular momentum shifter, where the angular momentum is as important to his walking as is moving his center of gravity. 

If you look carefully, you will realize that Go-Rilla, DSDK AT-ST, and Super Battle Droid all the same basic design principal that Yoccha invented in his fabulous Demi-God of Pure White (Half-God Walker.)

The result is a fast aggressive walker that is quite stable. He is by far the fastest biped I've ever made, both relative to body height, and in absolute speed.

He occasionally gets his feet tangled, which can get the side to side motion out of sync with the forward backward motion of the legs. Re-tuning the drive train is relatively simple.

Step 1 - align the axles coming forward out of the hips so they are even with each other, and that the left hip's 1x3 liftams are forward. Step 2 - slightly disassemble the hip as show in the the picture. See how the 3x5 quarter oval, the small pulleys on either side are slid forward? Notice this allows the red 12 tooth bevel can slide away from the other 12 tooth bevel. Step 3 - Turn the axle that makes the knee change shape, so that the 1x3 liftarms on the end are straight down. Step 4 - confirm that everything is still aligned in steps 1 and 3, and reassemble the hip. Repeat steps 2, 3 and four for the right hip.