[Frank Neuperger]

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!