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.

Re: Kicker Help?
 

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?

Re: Kicker 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?

Re: Kicker Help?
 

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.

Re: Kicker Help?
 

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

Re: Kicker Help?
 

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.

Re: Kicker Help?
 

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.

Re: Kicker Help?
 

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.

Video

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.

Re: Kicker Help?
 

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...

Re: Kicker Help?
 

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

Re: Kicker Help?
 

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)*(V*V)
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.

Re: Kicker Help?
 

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.

Re: Kicker Help?
 

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.

Re: Kicker Help?
 

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

Re: Kicker Help?
 

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.

Re: Kicker Help?
 

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.

Jason

Re: Kicker Help?
 

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! :)

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.

Re: Kicker Help?
 

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.

Re: Kicker Help?
 

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

Re: Kicker Help?
 

How did you do this calculation?

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

Thanks.


~

Re: Kicker Help?
 

For a given amount of stored energy (armed state of kicker), mass is inversely proportional to the square of the kicking speed.


~

Re: Kicker Help?
 

This web document has the most in depth math/physics analysis of ABSOLUTELY EVERYTHING relating to soccer!!
"The Science of Soccer" by John Wesson:
=> http://www.scribd.com/doc/6726997/ScienceofSoccer

Their analysis of kick, bounce and spin are useful, and worth reviewing briefly.
Some items covered include:
1) Professional kicks go 70+ miles per hour & contact with foot lasts ONLY 1/100 of a second
2) ball spin of around 10 RPS can accelerate a ball on landing by 5-10 miles per hour

Team 3135 will use a 3-4lb pendulum mass traveling at ~25-30 MPH at impact with the ball for a max contact distance of 3-5" to have it travel the length of the field, clearing both bumps at low "line drive" angle. Our bungee winder design can shoot at any point during the 2-3 sec (to full power) wind up, and also have programmed level of wind up to adjust kick strength.

We also will need to quickly (<1" travel) absorb the momentum impact of this kicker's momentum using synthetic cord tether.
-- Dick Ledford

Re: Kicker Help?
 

That fits with our findings. We used a 2 pound pendulum and had no problem kicking the ball with a low arc 40 feet.

The mass of a typical #5 bal is 0.4 Kg.
The mass of a typical player's leg is 6 Kg.
The coefficient of restitution is 0.7. This relates to the elasticity of the ball. e = (D2/D1)1/2. The ball bounces halfway to its starting elevation on tile, so D2/D1 = 0.5. The square root of 0.5 = 0.7.

If Vleg = 20m/sec then:

Vball = 20m/s x 6kg/(6kg+0.4kg) x (1 + 0.7) = 31.9 m/s = 72 mi/hr

If the ball is traveling 31.9 m/s, then 20m/31.9 m/x = 0.67 sec for the ball to travel 60 feet (20meters).

For 1.5 seconds, the launch speed is 13.3 m/s.

We assume the ball contact time is 0.01 sec

Force on the ball = mass of ball x acceleration

A = change in V/t = (13.3m/s - 0)/0.01sec =1330 m/s2

Force on ball = 0.4 kg x 1330 m/s2 = 532 Kgm/s2 = 532 Newtons = 120 pounds of force on the ball to launch 20 meters.

Re: Kicker Help?
 

Yeah, our team got the same results ours is a happy medium of about 2.75"