The RTL-SDR site highlights the work of Humpelstilzchen in getting a robot to drive towards a 433 MHz beacon transmitter
The experiment used a 433 MHz module to send out an FSK beacon.
On the robot two antennas are used for the time difference of arrival/pseudo-doppler direction finding technique, and PIN diodes are used to rapidly switch between the antennas. A GNU Radio script running on a Humming Board single board computer computes the TDOA/pseudo-doppler algorithm.
Hackaday - Wild Thumper based ROS robot - https://hackaday.io/project/25406-wild-thumper-based-ros-robot/