Kicker Help?

[Ether]

Originally Posted by Kevin Sevcik

He didn't mention it, but mass is inversely proportional to kicking speed.

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


~

[RRLedford]

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

[wexlerd1]

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.

[jamie_1930]

Originally Posted by billbo911

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*(V*V)
Kinetic Energy = mass * 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.

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

[billbo911]

Originally Posted by jamie_1930

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.
Thank goodness physics doesn't change just because you forget the formula.

[dtengineering]

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

[billbo911]

Originally Posted by dtengineering

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

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.

[baruffir]

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.

[jamie_1930]

Originally Posted by infocus

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.

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.