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Golf Ball Versus AL disc, and the emp launcher

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LAN_403

w1vlf

Tue May 13 2008, 06:19PM

Registered Member #1329 Joined: Mon Feb 18 2008, 07:31PM
Location: Harwinton Connecticut
Posts: 53

Hello Guys,

OK.. Here is the deal. I went to a driving range this morning and after explaining what they were going to be used for, the guy there gave me 2 golf ball.
50 cent KMart specials he called them.

"The games afoot"

Some stats

AL disc weighs in at 35 Grams
Golf Ball weighs in at 46 grams.

Range conditions
Dry
80 degrees
Slight breeze

Launcher power supply, 6000 uf at 900 volts
Mechanical contactor from a fork lift used as trigger.

Coil.. (Now falling apart) 4 2.5" dia coils stacked on top of each other and glued together and wired in parellel.
AL disc is 1/4" thick and 2.25" in dia.

All tests were made as close to vertical as possible.

Test 1 is the AL disc alone fired at 300 Volts
Time of Flight
A) 2.4 sec
B) 2.5 sec
C) 2.4 sec

Test 2 is the AL alone disc fired at 600 Volts
Time of flight
A) 4.6 sec
B) 4.9 sec
C) 5.0 sec

A small hole in the AL disc allows the GB to located in the same spot each time

Test 3 is the AL disc with the Golf Ball sitting on top of it fired at 300 volts
A) 2.1 sec
B) 2.1 sec
C) 2.2 sec

Test 4 is the AL disc with the Golf Ball sitting on top of it fired at 600 volts
A) 5.1 sec
B) 5.4 sec
C) 5.1 sec

Test 5 is the AL disc with the Golf Ball sitting on top of it fired at 800 volts
A) 7.6 sec

Test 6 is the AL disc with the Golf Ball sitting on top of it fired at 850 volts
A) 8.00 secs.

I could not charge to 900 volts or above since I did not bring the variac outside.

During all the tests using the golf ball, the AL disc just launched only slightly and was never more than 2 feet away from the coil when it landed.

Test 5 and 6 scared the crap out of my son and I as there was no way you could see the ball.

Now to find what the initial velocity is and how high the ball went.
Total weight of the AL disc anf the GB is 80 grams

PauLC
W1VLF

dingo27

Tue May 13 2008, 06:52PM

Registered Member #890 Joined: Tue Jul 10 2007, 10:06PM
Location: Slovakia
Posts: 180

are you planning to shoot plane?

nah... but interesting project. maybe you could use tennis ball instead of golf, you can see it better.

Firefox

Tue May 13 2008, 07:03PM

Registered Member #1389 Joined: Thu Mar 13 2008, 12:50AM
Location: Pittsburgh, PA
Posts: 346

Wow, that sounds like fun. My 1280 uF bank @ 300 V scares the krap out of my mom. Interestingly, the golf ball seems to lessen efficiency (for distance at least) at low energies (300 V) and then increase it at higher energies (600V). I'm thinking that at 270J the aerodynamic efficiencies don't compensate enough for the energy transfer between the ball and plate, while at 1080J you get into higher order drag forces, therefore the disk is horribly inefficient drag wise, and allows the aerodynamic ball to travel further than the plate would on its own.

Assuming that drag is negligible for the ball (which it quite clearly is not), the ball had an initial speed of 39.2 m/s (88 mph) in the 850V trial. That means (ideally) an apogee at 78 meters (260'), pretty impressive in my book. That also means an energy transfer from the coil to the ball is a little better than 1.6% (35 J/2167 J) which, while not excellent, is not terrible either.

At this point I would suggest trying to find balls of the same diameter, but different masses, and coat them in varnish (to take away aerodynamic differences). Then you could try to improve the energy transfer between the plate and the ball, and perhaps find the ideal balance between energy transfer, aerodynamics, and projectile mass. Making the armature (disk) lighter may also improve energy transfer, by making the ball heavier in comparison, and improving the transfer of momentum between the two objects, as the mass of the disk is no longer the only mass to hold the disk in the B field long enough to transfer all of the energy from the coil.

Shaun

Tue May 13 2008, 07:19PM

Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616

Your numbers sounded a little off Firefox...

8 sec fall time comes to 313.6 meters altitude. d=.5*g*t^2 g=9.8

It takes 141.4J to take a 46 gram projectile to that height (E=m*g*h), and with 2167.5J in the caps (6000uF @ 850V) bank that gives 6.5% efficiency.

A 46 gram ball with 141.4J of kinetic energy has a velocity of 76.8 m/s (E=.5*m*v^2). m=.046

Firefox

Tue May 13 2008, 07:21PM

Registered Member #1389 Joined: Thu Mar 13 2008, 12:50AM
Location: Pittsburgh, PA
Posts: 346

Its a 4 second fall time, and an 8 second hang time, not an 8 second fall time. It had to get up there before it could fall back down.

Shaun

Tue May 13 2008, 07:23PM

Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616

My bad, I used to do model rockets where we measured fall time.

Quantum Singularity

Wed May 14 2008, 01:36AM

Registered Member #158 Joined: Sun Feb 12 2006, 09:53PM
Location: Central Ohio
Posts: 282

Hey firefox, when you say the ball is hurting efficiency at lower power are you taking into consideration that the ball has more mass and your comparing it to a previous launch (just the disk) with less mass? Not sure, I didn't do the math, but of course velocity will be less when you add more mass to the projectile, that doesn't mean efficiency suffered unless you accounted for that.

Also, it sounds like the ball was placed directly on the aluminum plate correct? So there really is no 'transfer' from the plate to the ball, they are both launched together as one, with the same initial velocity, just that the disk separates early on so the projectile ends up with less mass.

Is there an easy way you could suspend the ball over top the disk so you do get a transfer like in your other thread? Well that might not work so well though, as you've indicated the ball is actually heavier than your disk, so you wouldn't end up with a higher initial ball velocity than your disk. I'd be interested though if you could try a heavier disk/lighter ball setup to see if velocity could be increased.

Firefox

Wed May 14 2008, 02:54AM

Registered Member #1389 Joined: Thu Mar 13 2008, 12:50AM
Location: Pittsburgh, PA
Posts: 346

I suppose transfer is not the correct word. However, with a lighter disk and a heavier ball (correct me if I am wrong) more of the energy will be stored in the ball if it is moving with the same v initial as the plate, which it should be if they are in contact from the get go.

Quantum Singularity

Wed May 14 2008, 03:41AM

Registered Member #158 Joined: Sun Feb 12 2006, 09:53PM
Location: Central Ohio
Posts: 282

Yeah, I call that the 'sabot' style, the velocity of both are the same but the projectile looses mass when they seperate so the energy of the projectile also decreases. In that style if the ball was significantly heavier than the disk, then the loss would be minimal.

So I guess there is two approaches, both utilizing the golf ball for aerodynamics. There is the sabot style, where you would want the ball to be heavy and disk lite for the projectile to retain as much KE as possible. Or the other method in which velocity is a goal, a lighter ball would be struck by a heavier disk resulting in a higher velocity but less KE projectile. Of course with golf balls I dont think you have a choice of weights do you? IDK, I have never golfed before.

FastMHz

Wed May 14 2008, 06:29PM

Registered Member #179 Joined: Thu Feb 16 2006, 02:08AM
Location: Hagerstown, Maryland - Close to Prime Outlets
Posts: 287

Hmmm....I need some golf balls

Too bad you're in Connecticut too.....darn....

I'm going to find out where a golf ball ends up with an IL fired at 24kj someday

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