Summary

Demo video https://youtube.com/shorts/muIV55Uja68?si=GNVSlOBg0-DXcMDJ
build video can be found here. https://youtu.be/BuRM82NZQZI
Using a low cost "around $1 dollar" IR obstacle avoidance sensor module and a low-cost Dual H-bridge motor driver" $1 dollar or less" , you can control a TT gearmotor with a 1-way bearing wheel to not fall off table tops or downstairs. I used a 1:48 dual shaft TT gearmotor as it is the most common version. The 1-way wheel is only used on the left side and inside the 3-part wheel assembly are located 2 B B's. The B B's allow the wheel to turn free in one direction and lock up in the other direction. There is a external latch arm to make sure the wheels locks up when the TT gearmotor reverses direction.
Two AA batteries supply the power for the device.
There is a small rear drag bump part you glue on to the rear base, the weight of the batteries and this bump part keep the front where the IR sensor is located floating.