Programming Robots Study Group
Robots are coming! Let’s be ready to program them.
This study group is ROS centric. Class material will be based upon Ubuntu 14.04, ROS Indigo and Android. Other operating systems may work but we chose Ubuntu as it is ROS’ supported platform.
We’re targeting a simple, inexpensive platform. The magician chassis is simple, inexpensive and easy to assemble. It’s sufficient for an initial platform.
This is what the motor look like.
Note the extended back shaft. Now I got these motor out of a kit from servocity.
Now i got Magnetic Encoder Kit for Micro Metal Gearmotors from Pololu. Now it is designed for their Micro Metal Gearmotors. Which are smaller then the above. After a modifying both the magnet and circuit board. The encoders provide a resolution of 12 counts per revolution of the motor shaft when counting both edges of both channels. To compute the counts per revolution of the drive sprockets, multiply the gearboxes’ gear ratio by 12
Quadrature encoder transitions are often detected by monitoring both encoder channels directly. However, since transitions on the encoders can occur at high frequencies (several thousand per second) when its motors are running, it is necessary to use the 32U4's pin change interrupts or external interrupts to read the encoders. To reduce the required number of interrupt pins, I have XORs together both channels of each encoder and connects the resulting signal to an interrupt pin, while channel B of each encoder is connected to a non-interrupt pin: The XORed signal and the channel B signal can be used to reconstruct the channel A signal by simply XORing them again: (A XOR B) XOR B = A. For both encoders, channel A leads channel B when the motor is rotating in the forward direction; that is, A rises before B rises and A falls before B falls.
Right most of the work is going into writing code for the Teensy.
- H-Bridge driver
- Encoder driver
Datasheet