vee41 Thanks for your reply! :)
I've checked your sample, that's not flexible tought what happens if you add extra cooldown frames?
Actually we have 4 frames for Harvester, then duplicate last frame, duplicate another 4 frames, in total 8 frames. It altered the impact time. The observed result was it can impact by some cooldown frame, not frame number "2"
Do you think we can create new instance variable as "Impact Frame" we type 2 in value field which is related to impact frame?