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"