Kicker Help?

We’ve designed a mechanism using the bungee cords that can produce 75lbs of force at the end of our kicker. But we fail to move the ball over one bump. Is 75 lbs enough force? Or is it possible that there is something fundamentally wrong with our kicker design. Any help will be greatly appreciated.

Our robot and some other teams are using a combination of bungee chords and pneumatic pistons. If you use that and try your best to kick the ball at about 45 degrees you’d be able to clear about twenty feet uniformly. I’ve also heard of taking the pneumatic pistons and limiting how far the piston can pull back and that actually gives more room for pressure storage, giving the piston some more bang for you buck.
Does that help?

We’ve been prototyping the same concept, but for some reason can’t get more then 10 feet out of a shot. Could you offer us any more insight or advice?

75 pounds is A LOT. We’d have roughly 30-40 (50 pounds at our strongest) and we can get a decent 30-25 feet. It really also depends on how far away your point of rotation is sitting, generally farther is better.

If you don’t mind, post a picture/video of your setup, and that’d be better for us to help out.

Also, are you manually releasing it or is there a mechanism involved? Depending on what you’re doing, you could have a mechanism that’s burning too much energy in the release.

Try messing with the angle of incidence and size of kicker and see what you get. I would recommend messing around with wood prototypes because they are much easier to change/modify than metal/80-20.

We have come up with a design using surgical tubing included in the kit that is able to get the ball over the hump easily when a wedge is added to the end of the kicker. In one of our tests, we fired it after school down an empty hall way to see how far it would go, and it hit the ceiling almost knocking down a tile. It seams that noone has mensioned puting a wedge at the end of their kicker, and I think that is why you are not getting the lift to get over the hump. you have plenty of power, but you need lift to fly over the hump, or topspin to roll over it

I would bet it has to do with where you are striking the ball.
We found the best sucess by striking the ball 2.5-3" off the ground.

Our team has designed several that work well with surgical tubing. I’m not sure the force we use, but it isn’t much. We are, however, able to launch a ball quite some distance. You might be wasting lots of energy in your release. Also, the way that the kicker connects with the ball is important. We used a wedge to hit the ball causing it to go in more of a diagonal arc.

Well my team hasn’t completed our kicker design yet. but here’s a link to a team that we work with that has utterly beautiful performance on their kicker. Pause and study the vid a bit.


if you can’t access youtube because of blocks or whatever just click on my signature and you’ll go to my teams blog. I’ve posted the video of that kicker up.

It’s not my teams robot though. It’s a high school that were working with closely.

How much Travel do you have, in what ever hit the ball?
What is the mass of whatever is hitting the ball?
What is your config?

A picture would really help…

Could you guys please explain what you mean by a wedge? Just what kind of shape, what angle its at, etc.

Some basic things to consider are:

  1. Maximize impact velocity on the ball.
  2. Make sure the kicker follows through on the kick.
  3. The mass of the kicker is not as important as the velocity, but it helps.

Ke = (M/2)(VV)
Kinetic Energy = (mass/2) * velocity squared

Maximizing kicker velocity will also help compress the ball. The ball will return that energy in the form of velocity, and distance, if it is still in contact with the kicker when decompressing, thus the need for follow through. Having more mass will enhance this process as it will the kicker to not decelerate as much when the kicker impacts the ball.

Second Bill’s suggestions. Once you have enough mass that the kicker isn’t stopping upon impact with the ball, velocity is the primary driver of kicking distance. He didn’t mention it, but mass is inversely proportional to kicking speed. More mass = less speed = less kicking distance. I’d recommend lightening your kicker until you start seeing diminishing returns in kicking distance.

The first thing I would look at changing would be what is hitting the ball. We are still optimizing this, but 30-50 degrees (from vertical) is the range we have determined to be the best so far for the angled plate we have attached to our leg. Also some people aren’t thinking realistically about how hard or far you need to hit the ball. Remember your never going to be 18ft away from the bump because in the far zones there is only 17.5ft from wall to bump and 17ft in the middle, plus your robots dimensions will take up some of that space, so plan that the max, if your right up against the wall would be around 15 to 14ft, depending on your robot’s dimensions. Also your not going to be right up against the wall so make sure you try seeing if you can just change the distance your firing from.

Kinetic Energy = (1/2)m(v*v)

OOOoooops, you are absolutely correct. I have edited my post to reflect this.
Man, it has been a long while since I had that physics class. :o
Thank goodness physics doesn’t change just because you forget the formula.

If you watch the videos that some teams have posted, you’ll see kickers that can really put some energy into the ball, up to, and including, knocking clocks off the wall.

We’ve gone a different route, limiting the height of our kicks so that we just barely clear the first bump, bounce, and then clear the second bump and roll into the goal. The idea is that if we can do that… and never kick the ball higher than the top of the goal, that we can possibly get away without having to adjust kick strength.

We also don’t want to kick the ball too high, as a low trajectory reduces the chances of accidentaly kicking the ball over the wall and drawing a penalty.

So don’t feel that you need to have the most powerful kicking system going. That’s cool… but probably not necessary.


Well, now that the cat is out of the bag…

That is the approach we will be taking as well. Consider that one of the only limitations this might have is when you try to shoot point blank into the goal. Too much force might cause the ball to rebound back out. If you know this limitation, you can compensate for it.

Otherwise, if positioned properly in zone two, you can put it in the goal in zone one easily.
In zone three, one bounce in zone two then over the second bump and into zone one, then into the goal! :slight_smile:

The other limitation this approach might have is during Autonomous if you have multiple balls in line with each other. The first ball might not clear the next. But again, if you know this, you can compensate for it.

Cut a 4" piece of 2x6. Cut a 45 degree corner off the short way, not the long way. It should look something like this from the side:


Attach this to the end of your kicker. We had issues clearing one hump before. Now that we’ve added this, it clears two humps easily.

We calculated that about 100 pounds of force exerted on the ball with a contact time of 0.01 seconds would launch the ball 20 meters (60 feet). The kicker would contact the ball at 7m/sec which given a coefficient of restitution of 0.7 for a soccer ball means a launch speed of 14 m/sec.
We haven’t reached 100 pounds yet. Cocking the kicker prototype part way with a tight elastic spring results in a launch of about 40 feet. We think 60 feet should be feasible using this method.

Dan Wexler
Team 2547

How did you do this calculation?

Would you share your calculation so other teams could learn from it?