Gyroscopes and Accelerometers on a Chip

 

The interior of a 3-D MEMS Gyroscope Sensor is intricate and tiny (the width of this structure is only about 800 micrometers).
The interior of a 3-D MEMS Gyroscope Sensor is intricate and tiny (this structure is only about 0.08 cm wide).

My last two blog entries discussed demonstrations of gyroscopes and angular momentum conservation at our school’s science fair. One of the demonstrations I put together takes a look at how really small gyroscopic sensors, such as those in many smart phones, video game remotes or quad-copters provide information about their changing orientations. This information can be used as feedback for self-balancing (e.g. a two-wheeled scooter), navigation or as input to other applications like video games.

I didn’t want to sacrifice my smart phone for this experiment. Fortunately, chips containing gyroscopic sensors are relatively cheap. In reading up on gyroscopic chips, I found that orientation data from gyroscope sensors is prone to drift significantly over time, so gyroscopic sensors are frequently combined with additional sensors, such as accelerometers or magnetometers to correct for this effect. This combination of sensors is frequently referred to as an IMU, or “Inertial Measurement Unit”, and it is used in  airplanes, spacecraft, GPS navigators (for use when GPS signals are unavailable) and other devices.  The number of of sensor inputs in an IMU are referred to as “DOF” (Degrees of Freedom), so a chip with a 3-axis gyroscope and a 3-axis accelerometer would be a 6-DOF IMU.

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Buidling the Anyway NXT Scooter

The "Anyway" in profile
The “Anyway” in profile
The "Anyway" self-balancing scooter -balancing itself.
The “Anyway” self-balancing scooter – balancing itself.

As I mentioned in my last post, my sons’ school had a science fair last week where I ran a demonstration involving angular momentum and gyroscopes.  In researching the use of gyroscopes in engineering today, I found that extremely large gyroscopes, weighing up to hundreds of tons, are used to stabilize ships, and extremely small gyroscopes that operate by vibration are used in electronic circuitry, such as that in smart phones and video game controllers.  One application that many people are familiar with is the use of gyroscopic sensors to stabilize self-balancing two-wheel scooters, like the Segway.

Googling “self-balancing robots” reveals a remarkably large number of homemade robot

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Fun with Angular Momentum

Demonstrating the conservation of angular momentum with a bicycle wheel and rotating stool.
A young experimenter demonstrating conservation of angular momentum with a bicycle wheel and rotating stool.

Last weekend my children’s school had a science fair which they called “STEAM Day”, for Science, Technology, Engineering, Arts and Math. It turned out to be a engaging and dynamic event, with lots of great demonstrations and activities for the children, ranging from kindergarten to 8th grade.

I volunteered to run an activity demonstrating angular momentum conservation, which was titled “You Spin me Round”. Our primary demonstration used a large gyroscope made from a bicycle wheel with two handles, like this one here. I (and my oldest son, who was my assistant) would spin up the bicycle wheel, and carefully hand it to a child who was sitting on a stool that was free to rotate. We then told the child to tilt the bicycle wheel to the right or the left. They were usually surprised to find that the spinning wheel “resisted” this change, and that they would start to rotate in the direction in which they turned the wheel! One tip I would recommend for anybody else trying this experiment – it was tremendously helpful to have work gloves for use in spinning up the bicycle wheel. After several hours, the palm of my hand was bruised and sore!

The children were too young to understand a detailed explanation of angular momentum conservation using torque and angular momentum vectors, 

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