Hello everyone! I'm Professor Scientifik and I just finished creating my first biped robot. It's named “Maestro”. Before I continue, I would like to thank (even if I don't know him personally) Jeff Owrey. He has writen a really useful and amazing document called bNXT Avoiding Obstacles With The Alpha Rex. This document will solve all your problems concerning Alpha Rex like when he's not walking and stuff like that. Guaranteed!
About this creation
Building Description: Okay, you guys are probably now thinking "Aww, this weird professor sucks, he used Alpha Rex's legs!". Yes, I did use his legs, but I did my own stuff too. Basically, this robot uses an ultrasonic sensor, a sound sensor, a light sensor, a touch sensor, two motors and an NXT intelligent brick. You can build this robot with the 8527 NXT set or, in other words, with the retail NXT set. I have the LDD here, but I couldn't completely build Alpha Rex's legs on LDD due to bugs and glitches, so some parts are missing. Just build it using the brick command center (click human>Alpha Rex>Walk>Building Guide), but skip step 45. However, the things that really need instructions are in the LDD. Basically, I just want to say that you can build Maestro using LDD and the Mindstorms instructions. As well, I want to point out one of Maestro's features; the arms swing back and forth while the robot is walking.
A little theory: If you guys have build the Alpha Rex, you should have come to such problems as he “He doesn't walk straight!” or even “He doesn't turn!”. In this section I'm going to make a little nutshell of Jeff's document. First, you should take in note that the motor located in the robot's left leg tilts the robot from side to side. What this little movement does is that one leg loses it's friction and the other one gains friction. Here's a scenario:
The robot tilts to the right. Next, it strides it's left leg forward. It is done with ease as all the weight is on the other leg. If you don't know yet, Alpha Rex's legs move simultaneously (one forward while the other backward). Now, if the left leg strides forward, the right leg strides backward. Because all the weight is concentrated on the right leg, the right leg gains more friction and due to this, when moving backward, it pushes the robot forward. Then the robot tilts to the right and this process restarts. I hope this is clear enough...
Now, I'm going to explain how the robot turns (this means “Get ready for another long and boring explanation...”). To turn, the robot has to put his weight on both legs, which means that it has to tilt back to the center. Next, it has to tilt left, move the right foot forwrd, tilt back to ceter and then move the left foot forward. This is just a considerable, but not complete turn. You will have to repeat this operation I think around 2 times to get a 110 degrees turn. Anyways, I really suggest you guys read Jeff Owrey's document and try to understand its content (I had to read it twice to understand it).