GrabBob, a 4 fingers wiimote controlled grabber

Hi Everyone!

It' s been a long time since I have not built a grabber. And this time, I tried to do an unsusual one:

Most LEGO grabber arms use 2 different axis to open or close the hand. It actually is the most eficcient way to make a good grabber, and I first wanted to do one like it. Still, a friend of mine asked me if I could build a grabber like the one in the movie "Iron Man" : the main character has a small cute fellow grabber, whith 3 fingers on different axises. Considering that it' s very hard to deal with triangles in LEGO geometry, I decided to make it 4 fingers.

I had to use a small trick for the linear actuator to open or close the hand, as you can see on the video below, but building the grabber was not the main difficulty.
I actually had a lot of trouble to make the grabber rotate on its base, because of the high torque that was applied on the axis. I didn' t use the part 48542 because it involved way too much friction. So I decided to tinker something, still the result is pretty lousy.

The wiimote has 3 sensors : an hitechnic accelerometer, for the wii-like control, a light sensor, to control the opening of the fingers, and a touch sensor, only to stop the robot ( I only use the touch sensor to put the robot back in its initial position).

Obviously, it is not a good grabber! Anyway, I had a lot of fun building and programming it, and it' s kind of a pretty robot. ^^

Bobly yours

BiBob, a dynamic biped walker.

Hi everyone!

The problem of the biped walker has exicted every robot maker at least once! But one problem that is not often very well known is the one of the "dynamic" biped walker... Let me explain:

Most of lego biped are "static" walkers : their stability criteria is to keep their center of gravity (COG) inside their footprints. It works pretty good, but if you just look at the way you walk, you'll realise that you actually don' t move your own COG( which is approximately located behind your navel) on top of your feet.
That is because your body is embedded in its own movement, it' s the phenomen of inertia. It is the same kind of forces that pushes you when you suddenly slow down whith your car.

A "dynamic" biped is a walker that masters inertia (like any humanoid robot today). When the robot is moving, the point to keep inside the footprints is not exactly the COG, but a point called ZMP ( Zero Moment Point). If some of you are interested, it is the point on the floor where the sum of the torques of the forces of inertia and of the weight is equal to zero.
You can find more iformation about the ZMP here.

I skip all the boring math stuff I had to perform to make sure to keep BiBob's ZMP inside its footprints, just note that I had to modelise BiBob whith the software SolidWorks (my school owned it) to get the properties of mass, as shown on this picture.

I was so able to know what trajctory give to the robot to have a good enough tajectory of the ZMP.












And finally, the robot walks pretty good, here is a video of BiBob walking :



Bobly yours.

The Bob Factory is created!

Hi Everyone!

I finally decided to create my own Lego mindstorm NXT Blog. I will here show you my Lego mindstorm NXT projects, and explain them as good as I can!

Every robot I make is part of "The BOB family", and BOB stands for "Bobs Ought to Be".

Have fun exploring the blog, and if you want to criticize some of the robots I will show you, don't hesitate, no robot is perfect, and I will try to enhance them with your precious remarks!

Bobly yours.