I'm not allowed to say this, because a moderator admonished me before.
But if you pay me, I'll just write it, with a timer for fall time to damage rate.

But for free info, when using timers, makes sure time_step is in place, also you need extra steps to keep the frame rate in line, last if testing in window mode - for heavens sake lock the fps to 60 or you random fps shift can be as large as -100/+100 fps