Hi, does anybody know how I can make a failsafe system to shut down if Rc signal is lost,

You could build one in theory, but they are so cheap from RC shops that it is just not worth your time.

you can just buy em yes or if you dont wanna fork out for one per channel you could have it so a servo running from one failsafe when it failsafes hits a microswitch running to power which kills the whole robot
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Andrew Welch, Team Unconventional Robotics