Tag Archives: gyro

Guide to interfacing a Gyro and Accelerometer with a Raspberry Pi

A lot of people have asked how I got the readings from the Gyro, Accelerometer, and Compass inertial measurement unit(IMU) which is used to keep PiBBOT upright.

UPDATED And updated guide has been published here, with cleaner and simpler code.
BerryIMU Raspberry Pi Gyroscope Accelerometer

In this guide I will explain how to get readings from the IMU and convert these raw readings into usable angles. I will also show how to read some of the information in the datasheets for these devices. The theory and principals below can be applied to any digital IMU, just some minor modifications need to be made. Eg register values, sensitivity level…

The code can be found here;
https://github.com/mwilliams03/Raspberry-Gyro-Acc

A note about Gyros and Accelerometers

When using the IMU to calculate angles, readings from both the gyro and accelerometer are needed, which are then combined. This is because using either on their own will result in inaccurate readings.

Here is why;
Gyros – A gyro measures the rate of rotation, which has to be tracked over time to calculate the current angle. This tracking causes the gyro to drift. However, gyros are good at measuring quick sharp movements.

Accelerometers – Accelerometers are used to sense both static (e.g. gravity) and dynamic (e.g. sudden starts/stops) acceleration. They don’t need to be tracked like a gyro and can measure the current angle at any given time. Accelerometers however are very noisy and are only useful for tracking angles over a long period of time.

Here is an excellent tutorial about accelerometers and gyros;
http://www.instructables.com/id/Accelerometer-Gyro-Tutorial/?ALLSTEPS

Setting up the IMU and I2C

The IMU I use is a MinIMU-9 v2 Gyro, Accelerometer, and Compass which uses a L3GD20 3-axis gyroscope and a LSM303DLHC 3-axis accelerometer and 3-axis magnetometer.
The datasheets are needed if you want to use these devices;
L3GD20 datasheet
LSM303DLHC datasheet

This IMU communicates via the I2C interface.

From the images below, you can see how to connect it to the Raspberry Pi. You can also see the orientation of the X, Y and Z axis.

Temp 12 hour Graph Graph

Continue reading Guide to interfacing a Gyro and Accelerometer with a Raspberry Pi

Success with a Balancing Robot using a Raspberry Pi

I have had success with getting PiBBOT to balance.

 

 

 

When I saw my first two wheel balancing robot I was very fascinated.  And after receiving my Raspberry Pi, I decided to build one myself.
PiBBOT (Pi Balancing roBOT) is my first successful balancing robot. And it has room for improvement and extra functionality.

When building PiBBOT, I had a few roadblocks I needed to overcome;

  1. I originally had the Anker as the power source for both Pi and the motors, however the amperage was too low.
  2. Original H-Bridge not powerful enough for my motors
  3. Gyro calculation off by 15 degrees


The TFT displays the angles from the accelerometer, gyro, complementary filter and power to the motors.
The buttons are to turn the motors on and off and to reset the gyro.

BerryIMU Raspberry Pi Gyroscope Accelerometer

What next?

  • Incorporate the wheel encoders for better balance
  • Build a sturdier frame
  • Implement direction control
  • The able to self right itself after falling over
  • Room mapping
  • Retrieve a can of beer from the fridge
PiBBOT PiBBOT TFT Motor Controller
PiBBOT TFT PiBBOT PiBBOT TFT


PiBBOT consists of these components;
Adafruit:
TFT; 2.2″ 18-bit color TFT LCD display
RF Receiver :RF M4 Receiver – 315MHz

Pololu;
Motors;  9.7:1 Metal Gearmotor 25Dx48L mm with 48 CPR Encoder
Wheels; Pololu Wheel 90x10mm
IMU; MinIMU-9 v2 Gyro, Accelerometer, and Compass (L3GD20 and LSM303DLHC).

Anker;
Battery; Anker® Astro3 10000mAh  5V / 9V / 12V 2A Dual USB Output External Battery

Tenergy;
Battery; 7.2V Tenergy 3800mAh Flat NiMH High Power


Continue reading Success with a Balancing Robot using a Raspberry Pi

PiBBot – Robotic Project – Phase 2 – Prototype

Here is my first attempt at getting PiBBot balanced.

This is a very early prototype, confirming that all the hardware works and the I can get the time of the main loop down to 20ms, which was easy.
This prototype also helped me get my head around the code and math need to balance.

 

 

I am waiting on the delivery of some hardware to build my final and larger version.  Which will have a battery pack placed up high, this will help a lot with the balancing.

1stBalance2

 

The main components used to balance this prototype;

  • MinIMU-9 v2 Gyro, Accelerometer, and Compass (L3GD20 and LSM303DLHC Carrier)
  • Solarbotics GM6 120:1 Mini Gear Motor Offset Output
  • Dual H-Bridge Motor Driver
  • 315MHz RF M4 Receiver
  • 12v battery

The receiver allowed my to change the PID values in real time.

There is also a lot of other components on the breadboard, but they are not needed to balance. Eg TFT, 8x8Matrix, Temp monitor…



Continue reading PiBBot – Robotic Project – Phase 2 – Prototype