I've revised the circuit to provide noise rejection and safer power-up, as per the attached.
R3/C1 slug the circuit response to reject spurious trigger pulses less than 0.1 sec duration. R5/C3 and R8/C6 provide power-up reset to the 555s. Q1 has been added to prevent spurious motor turn-on during the 1/2 sec delay.
Edit: It might be an idea to add a push-button 'emergency stop' switch between the RESET input of 555 U3 and ground.
R3/C1 slug the circuit response to reject spurious trigger pulses less than 0.1 sec duration. R5/C3 and R8/C6 provide power-up reset to the 555s. Q1 has been added to prevent spurious motor turn-on during the 1/2 sec delay.
Edit: It might be an idea to add a push-button 'emergency stop' switch between the RESET input of 555 U3 and ground.
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