Optimal Linear Puncher Motion

I was wondering about the motions of linear punchers and would like to ask which is better:

  1. Hitting the ball at the end of the puncher’s motion (quick impact)
  2. Throwing-the-ball-motion where the ball is moving with the puncher

Option one is normally better as it allows the puncher to accelerate faster and then it will transfer it’s energy to the ball.

If you want to get a better understanding of which one you should use, do this:
Have someone punch you (softly - I’m not promoting violence) and push you much farther than the point at which they first contact you. Then, have someone punch you and immediately take their hand back. Which one hurts more?

As long as they use relatively the same amount of force for both punches, you’ll find that the immediate contact and retraction hurts more.

Thanks for the analogy! I get it now

No problem. Glad you got it!

I feel like I should step in here to clear up some big misunderstandings that are showing up.

Unfortunately, this analogy is completely off. The problem is that impacts and damage are based upon both force (at impact) and energy transfer in a way we aren’t exactly looking for them. Let me give examples that follow @The Electrobotz 's analogy that you can see are totally off.

First let’s look at pain v. transferred momentum or kinetic energy to a body as a whole. Case 1: A car drives along at 20 mph and hits you, slamming on the brakes right when it hits you. Case 2: You sit in the seat of a car as it accelerates gently up to 100 mph. Which hurts more? Cast 1. Which could launch you off of a ramp further? Case 2.

Now, if you’re worried about comparable speeds, let’s look at something else. You throw two eggs very quickly at the same speed. Case 1: The egg hits a thin glass window, bursting as it passes through the window. Case 2: The eggs hits a bedsheet held at its corners and stops without breaking. Which hurt the egg more? Case 1. Which transferred more momentum and kinetic energy from the egg, changing its speed the most? Case 2.

Also, you really don’t want to use this drawing the hand back bit. For example (since I’ve done the calculation out carefully in the past), if you strike with an axe and release its handle instead of hanging on, you lose an immense amount of the strike. And that’s not even with pulling back. Pulling back reduces the impact even further. You could punch someone with a very fast-moving hand and, if you could pull back fast enough, not actually hurt them.


So, what do we care about here? We don’t want to damage the ball. So we don’t want too much force at once. But that’s unlikely. Too much pressure is more likely, so make sure your puncher doesn’t have a pointy end that strikes the ball, not that you were likely to make it that way. What we really want to know is what transfers the energy stored as potential energy in the elastics into the ball as kinetic energy as efficiently as possible. Any energy left over in the elastics or the puncher will mean the motors had do too much and the batteries had to get too drained to get the ball going at that speed. This is where @Download Complete 's statement comes in:

If the puncher and ball travel together, then the punch is moving as fast as the ball just as the ball launches. Then you have a lot of kinetic energy in the puncher. Only if the puncher has essentially no mass (think slingshot rather than puncher) will the ball be given most the energy. But if you get the mass of the puncher small enough (close to but slightly greater than the ball’s mass) and make the puncher strike the ball, you will get a behavior like you see in a Newton’s cradle. The puncher will stop and the ball will launch. A little energy will be lost in the collision, but by far the majority of it will be given to the ball.

As to @Download Complete 's other point, a faster launch means it will be harder to play defense against the robot. The longer it takes to fire, the more time the shot being made is vulnerable.

Meanwhile, as to that whole pulling back thing, avoid it. Make sure the puncher can move a little bit beyond where it first strikes the ball. You want it to stop because of the collision with the ball, not because you do something else to stop it. Yes, you’ll want some sort of limit so it won’t accidentally dismantle itself if it fires without a ball and so it gets pulled back from the same spot each time. But set where the ball and that limit are so that the ball does the stopping of the puncher. This will also reduce the damage on the puncher and whatever sets the limit.

the answer is neither. the best option would be hitting the almost at the end of the puncher’s motion and then continuing a little further. It’s the same reasoning for baseball and soccer. You can kick or hit a ball with a bat way farther than you can throw a ball, but if you kick the ball and quickly draw your foot back or hit the ball and stop the bat dead, it will not go as far. that’s why you follow through. That is the best option. Hit the ball and follow through. (and don’t stop abruptly. you’ll damage the robot)