Mother Goose

The development of mother goose started in 2002. It was designed to cooperate with papa goose type robots. Mother is tracked robot that is relatively small to allow for high mobility. It has nevertheless quite some on-board computation power and a full sensor payload. Like the papa goose design it is meanwhile replaced by the rugbot robots.

Mother-goose is with a footprint of 400mm × 300mm much slimmer than the papa goose robots and hence suited as an alternative system for more constraint spaces. With its tracked drive, it is designed to negotiate stairs. To save weight and space, mother-goose is equipped with an embedded PC. The locomotion system as well as some of the basic sensors are implemented with the CubeSystem.

The main design goal for mother goose was to shrink the size of the robot compared to papa goose. This mainly had consequences for the on-board PC, which has to be an embedded solution which fits the size and power constraints. Furthermore, the opportunity to explore an other locomotion system was used and a tracked drive was designed.

The tracked drive of mother goose is based on off-the-shelf belts for power transmission. The belts are double acting, i.e., they have a profile on both the in- and outside and they are therefore especially suited as tracks. The synchroflex belts with T10 profile used for mother goose are available in various lengths and widths. We chose the maximum standard width of 50 mm. The acting length is 1250 mm, leading to a set-up with 480 mm footprint and a front wheel with 127.5 mm elevation above ground. The wheels are standard pulleys. The four bottom wheels are passively rolling along while the elevated front pulley is used to drive the belt and to propel the base.

The locomotion system of mother goose is powered by two motors with 90 W power, a planetary gear-box with 66:1 reduction and quadrature encoder with 500 pulses per channel. The complete motor-units have an overall length of approximately 150 mm. Therefore a transmission is used to mount the motors perpendicularly to the drive axis. For this purpose, universal joints were chosen as they are very lightweight and can transmit high torques. Alternative solutions like bevel gears are much heavier, namely in the order of several kilograms, to transmit the required torques. The universal joints have the disadvantage that they require precise assembly. Slight misalignments already lead to jamming and severe wear-out.

The main voltage of mama goose is 24 V. It is supplied from two lead acid batteries with 7.2 Ah. In addition to its CubeSystem components, mother goose is carrying an embedded PC. Its CPU card runs on a National Semiconductor Geode processor, a GX1 at 300 MHz, with 256 MB SDRAM and a CS5530A chipset. The embedded PC has 2 RS-232 ports, one being used to interface the CubeSystem and one for a Hokuyo laserscanner. The bus board of the PC has two PCI slots. One is used for a WLAN-card, the other one is used for a card providing four USB 2.0 ports, to which the two cameras are connected.

The laserscanner on mother goose, a Hokuyo Automatic PB9-11, covers 162 degrees in 91 steps up to a depth of 4m. In addition mother goose has two ultrasound sensors with a medium range of up to to 7 m and a narrow scan angle of 10 deg. To estimate the absolute orientation of the robot, two digital compasses are used. The first one is based on the Philips KMZ51 IC. It has an I2C interface and it is directly connected to the CubeSystem. The second compass is from Honeywell. Its RS232 interface is serviced by the onboard PC. The motors of mother goose are equipped with high resolution quadrature encoders. The software modules of the CubeSystem not only use this data for control, but also for odometry and dead-reckoning to estimate the robot’s pose. In doing so, the data from the compass is used for a leaky update of the orientation estimation via odometry. By this, the performance of dead-reckoning gets significantly improved.

The main drawback of mother goose was the limited processing power of its onboard PC. It is hence completely replaced by the rugbot series of robots.