Replacement Track Ball Ordering Information (link, details)

Technical Kit & Additional Hardware
1

I just got off the phone with Joel of SportGo. On Noon Friday they reached an agreement with FIRST that they would be carrying the replacement parts.

Free shipping on orders over $50 for FIRST components

Their website, and first components, are at
http://sportogo.com/index.asp?PageAction=VIEWCATS&Category=402

Phone number: 661-321-4937

Replacement bladders (6 pack):
http://sportogo.com/index.asp?PageAction=VIEWPROD&ProdID=297

Replacement Skins (2 pack):
http://sportogo.com/index.asp?PageAction=VIEWPROD&ProdID=301

Replacement Ball (entire unit)
http://sportogo.com/index.asp?PageAction=VIEWPROD&ProdID=299

Since some of this information was buried in another thread waaaaay at the bottom I’m putting it in it’s own topic.

Good luck!

2

I just had a detailed discussion with Sportogo.

Sportogo says they were the vendor to FIRST for the trackball cover but not the ball.
The FIRST balls (bladder+cover) weigh 7.1 to 7.2 lbs. We did this measurement on a really good load cell.

The FIRST ball cover weighs ~1.5 lbs (weighed by Sportogo on spring scale with 1/10 lb graduations). This would suggest that the FIRST bladder should weigh 5.6 - 5.7 lbs.

The $20.50 Sportogo ball SP01501 weighs 4.4 Lbs (per Sportogo) and does not have the “anti burst addative” that makes the PVC have the closed cell foam texture.

The $30 Sportogo Ball SP100001 weighs 4.8 lbs and does have the antiburst addative.

Yes, the Sportogo web site lists the bladder weights as identical but they tell me they are not identical and gave me the above numbers.

**Both of the above bladders are almost 1 lb underweight. We are still on the hunt for the EXACT FIRST bladder. ** The weight (mass) is pretty important for catapult development and the energy needed is E= mgh

Note that we did repair the 1.5 inch laceration in our ball by using PVC cement (the stuff for PVC pipes) and a patch made from a deflated 8" PVC ball of similar material (no foam) and clamping overnight. It seems to be holding air. We repaired the tear in the cover using an iron on patch before inflating the patched bladder. Be carefull with the temperature of the iron!

3

Did you account for the weight of the air in the ball? With that large volume of air it wouldn’t take much pressure to give you the extra pound. I believe some threads mentioned 2-3 pounds mass at 1 atmosphere (I haven’t checked their calcs), so only 5 psig would give you an extra 1 pound net weight (the first 1 atmosphere’s worth doesn’t show up as weight because it is offset by the same amount of buoyant force).

4

Update, in desparation we ordered a bladder from Sportogo. They said they had one real FIRST bladder (possibly a sample to compare to thier own) and we got it shipped. I had them weigh the FIRST bladder and the $30 bladder and they indicate that they both weighed the same… 4 7/8 lbs). We will definitely weigh it when it shows up on Monday. With 1.5 lb cloth skin, this does not add up to 7.2 lbs. Could be a scale calibration issue at Sportogo or the air mass issue mentioned below.

Garry, good point on the mass of air. Lets see how the numbers shake out. From some experience with inflatable stuctures, gut tells me that it is less pressure than 5 psi. Pressure vessel methodology for calcs.

For such high pressure (5 psi) with that large diameter the tensile forces in the skin would be really high. Hmm … lets see a one inch wide stripe with a diameter of 40 inches would have an area (area that force acts on in one dimension) of 40 sq inches. Think of this as side view of a barrel hoop. 40 sq inches wth 5 psi is 200 lbs that is supported on 2 sections of the band. So the “band tension” in a one inch strip of material is 100 lbs. This sounds like a lot of tension in that material. Think of the bladder when underinflated by say 1/2 inch and not pressing on the cloth skin. Would a 1 inch strip of that foamed PVC hold 100 lbs? Gut says no. Looking at it another way, it is the same skin tension you would have in a 10 inch diameter ball filled to 20 psi. That is one very very hard volleyball at 20 psi. Gut says 1 psig max. Mass of air is 1.19gm/liter ball is conveniently 1 m dia so 4/3pir^3=vol = 0.524 m^3 =524 liters = 623 gm = 1.37 lbs mass at 1 atm. Assume 15 psi =1 atm. Even at 5 psig (20 psi abs). you have 1/3 of 1.37 lbs = 0.45 lbs net weight. With 1 psig you have 1/15 of 1.37 lbs net weight= .091 lbs net weight.

We will update thread when we get the new bladder.

5

After pondering this some more and trying a different method to work out the energy for catapulting , I have the following thoughts.

The ball shows 7.1 lbs when I weigh it with a scale. I had been treating 7.1 lbs as the mass of the ball for purpose of catapulting it… i.e. accelerating it to a particular velocity to be able to go to a height to acheive the Hurdle. That is because the scale does not show (most of) the mass of air in the ball. Yes it is true that the external atmosphere largely cancels the “weight” effect of the mass of air in the ball because the air in the ball is likely to be only 1 psi greater than atmospheric pressure. On the surface, it would seem that we still need to accelerate the entire ball mass mass and that would seemingly take more energy than accelerating the ball only.

From the above post, assuming 1 psig inflation, I estimate that the mass of air in the ball that is immune to the “net” effect of gravity (invisible to my scale) is 0.623 kg or 1.37 lbs. Net affect of gravity is considering the effect of buoyancy of the atmosphere acting on the ball. 0.091 lbs weight is from the overpressure does see the “net” effects of gravity. This 0.091 lbs is included in the 7.1 lb weight of the ball when I weighed it. i.e. the uninflated ball should weigh 7.01 lbs

Thus the mass of air in the 1 psig ball is 1.37+ 0.091 lbs = 1.461 lbs mass. This is 17.2% of the mass of the 8.47 lb ball.

Is it possible that the mass of the buoyant (zero weight) air in the ball is not a real issue for the purpose of calcuating hurdling height,velocity, energy? The buoyant air I speak of is the 1.37 lbs at 1 atm and not the 0.091 lbs mass due to the inflation pressure of 1 psi over atm. .

I am thinking that once the buoyant (zero weight ) 1.37 lbs of air is accelerated, it has kinetic energy… yet it is immune to gravity. As such, this kinetic energy is eventually depleted to propel upwards the components that have the net weight. Is this why punching a day old helium balloon upwards results in a slow motion parabolic trajectory (including ascent, and ignoring drag coefficient)?

Bottom line is that through the effect of bouyancy of our atmosphere, an 8.47 lbs mass ball has a weight of 7.1 lbs. It is like gravity has been reduced by 1- (7.1/8.47) or ~16.1% to 83.9% of g.

It appears that in the end, we do not need extra velocity for propelling the total mass of 8.47 lbs (vs velocity needed for 7.1 lbs) to get the height desired. Relations are: PE=mgh , KE=1/2 mv^2 —> h= (v^2)/2g, v=sqrt(2gh) where v = vlaunch.

This is as long as the mass is taken as the 8.47 lbs and g is corrected by a factor of (ball weight)/(ball mass) = 0.83825.

In fact, launch velocity of the ball is reduced compared to a scenario where there was no bouyant atmosphere and the mass taken as 8.47 lbs.

Sure some will observe that we could have ignored the bouyant mass for calculating the energy required to propel the ball to the desired height. This is true. The launch velocity and time of travel in teh kinematics calcs would however be incorrect if you do not use the above method of correcting g. Yes we have ignored air drag.

Hmm, the ball gets a bit of the slow mo effect that you would have on the moon.

Appologies for not doing this in metric as well.

Regards
Frank

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