I am trying to move the tri-track chassis using simple relays with 2n2222 transistors, when applying high signal to a relay, the robot starts to move without any problem, but when applying low signal to the relay, it sometimes takes few seconds before it is off (sometimes it takes 7 to 8 seconds before stopping), can anyone please help me to solve this problem?
Bare minimum we are going to need to see an accurate schematic. Images of the robot, motors, boards, wires, etc. would be a big help.
You could try putting something like a 10k resistor between the transistor base and ground.