Without analyzing the complete code, the steps to go are:

• Remove the delay function calls. These mostly delay the program in such a way that other parts are not executed in time or 'at the same time'.
• Instead use the milli command and check again time stamps (of unsigned long int type) to reach the delays you need.
• Create a state machine. This means in simple form that you use an enumeration (enum type) which can have one out of a set of values (like Stopped, Accelerating, Decelerating), for each 'states' you can define in your sketch.
• Use these state machines and times to move from one state to another, and while changing state (or during a state) you can perform the actions you need.

Without analyzing the complete code, the steps to go are:

• Remove the delay function calls. These mostly delay the program in such a way that other parts are not executed in time or 'at the same time'.
• Instead use the millis command and check again time stamps (of unsigned long int type) to reach the delays you need.
• Create a state machine. This means in simple form that you use an enumeration (enum type) which can have one out of a set of values (like Stopped, Accelerating, Decelerating), for each 'states' you can define in your sketch.
• Use these state machines and times to move from one state to another, and while changing state (or during a state) you can perform the actions you need.