For Chris Atkeson's KDC class I am developing a simple,
robust machine to balance on two wheels. The design goals have
been easy prototyping using standard parts.Carnegie Mellon University > Robotics Institute > Garth Zeglin > Research > Balancer
For Chris Atkeson's KDC class I am developing a simple,
robust machine to balance on two wheels. The design goals have
been easy prototyping using standard parts.
Any suggestions for a catchy name would be welcome.
A group of students in the class is building a actively counter-balanced arm for the base machine.
I have a file of notes I jotted after putting the parts together.
The onboard microcontroller is a LPC2103 on an Olimex prototyping board. I designed a simple daughterboard (PDF schematic) to connect it to a Spark Fun 5DOF IMU, the motor encoders, and the motor amplifier. The prototyping board includes a normal 9 pin serial port used for programming the board, debugging output, and the host data interface. It also has a JTAG port which could be used with gdb for in-circuit debugging.
The baseline software in C is available here. It is an I/O server which runs the sensors and motor amplifier, and communicates over the serial port with a control program running on a host computer which implements the controller.
Eventually, the balancing controllers can be implemented directly on the LPC2103. The onboard software can be compiled using the Gnu Compiler Collection (GCC) set up as an ARM7 C cross-compiler. Here are my notes on compiling gcc on a UNIX machine (tested on Linux and OS X).
The LPC2xxx chips come with a bootloader supplied by the manufacturer. NXP/Philips offers a free Windows downloader which can program a .hex file into the on-chip FLASH. An open source alternative is lpc21isp; here is a cached copy of the version 1.37 source; more recent versions might be found on the files section of the related Yahoo group.
The procedure for downloading a new image to the LPC2103 internal FLASH on the Olimex LPC-P2103 board is to move the BSL jumper to the closed position, reset the board, then run lpc21isp. When P0.14/BSL is held low at reset, the bootloader will take control and wait for the programming handshake. One jumper pulls P0.14/BSL low. The other enables automatically resetting the chip using the DTR serial port line, which is not necessary if the chip is manually reset. After lpc21isp is done, move both jumpers back to the open position and reset the board again or power cycle it, and the new code will run from FLASH.
lpc21isp needs to know the clock rate and the port to use. Here's a sample set of command switches:
lpc21isp-1.37 -control balancer.hex /dev/cu.USA19QWb13P1.1 115200 14746
Here are cached copies of data sheets for the components.
The most recent mass distribution as calculated by SolidWorks. The coordinate system origin in the center of the bottom face of the vertical aluminum spine. The X axis faces forward, the Y axis to the left, and the Z axis up.
This can be see in this scale sketch of the machine showing the relation between this origin and the wheel axis.
Mass properties of balancing-robot Output coordinate System : mass props Mass = 2.1 kilograms Volume = 0.00156 cubic meters Surface area = 0.538 square meters Center of mass: ( meters ) X = 0.0127 Y = -0.000318 Z = 0.256 Principal axes of inertia and principal moments of inertia: ( kilograms * square meters ) Taken at the center of mass. Ix = (-0.0421, 0.00177, 0.999) Px = 0.00592 Iy = (-0.0147, -1, 0.00115) Py = 0.0991 Iz = (0.999, -0.0147, 0.0422) Pz = 0.102 Moments of inertia: ( kilograms * square meters ) Taken at the center of mass and aligned with the output coordinate system. Lxx = 0.102 Lxy = 3.97e-005 Lxz = -0.00406 Lyx = 3.97e-005 Lyy = 0.0991 Lyz = 0.000167 Lzx = -0.00406 Lzy = 0.000167 Lzz = 0.00609 Moments of inertia: ( kilograms * square meters ) Taken at the output coordinate system. Ixx = 0.239 Ixy = 3.12e-005 Ixz = 0.00276 Iyx = 3.12e-005 Iyy = 0.237 Iyz = -3.88e-006 Izx = 0.00276 Izy = -3.88e-006 Izz = 0.00643
Page revision: April 19, 2007.
Garth Zeglin, Robotics Institute, Carnegie Mellon University.