Wednesday, August 15, 2012

"Reaction wheel" stabilizes bicycles and inverted pendulums

From Hack a Day:

These mechanisms use a "reaction wheel" that moves the object against any tipping action by rotating in the opposite direction. This is using the concept of conservation of angular momentum: wheel spins one way, object spins the other way to conserve angular momentum. So, the whole system moves against any tipping caused by external forces or inefficiencies.

The bikes have a reaction wheel mounted perpendicular to the main bike wheels. This first bike is from an Asian Youtube user and is a miniature bike. He also has a unicycle that moves forwards and backwards to stabilize in that direction, whereas a perpendicular reaction wheel stabilizes side to side motion.

The second video shows a full size bike and an inverted pendulum using this concept. (For a student's diploma thesis.)

Cheap flex sensors with electrostatic bags and masking tape

From Hack a Day:


Flex sensors change their resistivitiy when bent. These are DIY flex sensors made with electrostatic bags (Velostat) and masking tape. A zip tie is used for reinforcement. Two wires are attached to strips of the electrostatic material, with two more layers loosely sandwiched between these. This is taped together with a zip tie added.