The goal for 2018: Getting my robot to follow me. How can this be done? I checked a few options for this:

1. Visually e.g. with OpenCVs Find-Object or OpenCVs camshift. However after playing with them I haven't found them robust enough. Maybe my camera or illumination could have been better?
2. Ultrasonic as implemented by e.g. Robo-Dog. Seems to work good, but with limited range (few meters?) and you have to point the beacon towards the robot, that is not what I plan.
3. Radio: The ham radio people have a game called "Amateur radio direction finding" (also known as fox hunting) where the hams are trying to locate a small beacon by using a direction finding receiver. There is a small howto on a cheap self made Transmitter & Receiver "Foxy" available (german) that should provide a good starting point. However I plan do use a AVR with a 434 mhz ook transmitter as beacon and my old RTL-SDR as receiver. Antenna will probably be a HB9CV. On ISM 433MHz the reception antenna will probably end up as big as my robot, so moving to a higher frequency (868MHz to 2.4GHz) might be obvious.