When you raise your hand and run up to the ball, you aren't in a race to see how fast you can do this. Do kickers think at all? When you raise your hand, give time for your players to start running, so they can position themselves and you don't run as fast as you can to kick the ball, you jog up to the ball to kick it. All good onside kicks are done slowly and they usually are recovered. It gets on my nerves how bad these onside kicks are and how clueless the players are doing it.