$11 worth of WS2811s, 50 plastic cups, an Arduino Pro Micro, and FastLED makes for one awesome Sparkle Ball!
https://youtu.be/08JMrfNQboQ
Looks great! If I might proffer a suggestion (though it might be too late): painting the bottoms of the cups whatever colored paint (silver mirrored from krylong perhaps) would give you a boost of reflected light and help to hide the electronics inside, tiny though they may be.
Otherwise, nice job. I might put one together myself.
Nice. I’ve been meaning to make one of these for years. I saw it done with white cups at a decompression event years and years ago now, remember it looked awesome as the white color really let the light from the LEDs wash over the cups.
Totally cool!
Curious, I see a lot of the users here buy from Aliexpress. I’ve got and almost always buy from Amazon Prime. I’m not really seeing a huge discrepancy in price and with Prime, I always get free shipping. Any reason the preference (other than not having Prime)?
There’s usually a 15 to 20% difference in price when you shop around on Ali. It’s not much when you’re doing a one off, but some of us are addicts. 
It only makes sense to shop AliExpress in two situations: 1) It’s Singles Day (11/11; big sales). 2) You’re buying in bulk and don’t mind having to wait 3-6 weeks for the stuff to arrive. This is my primary reason and I usually combine reasons #1 and #2 to maximize my savings. The best deals are usually electronics components like LEDs (5m strips of waterproof APA-102 for $30 this year!).
I suppose there’s a third reason as well: The product can only be had from AliExpress. For example, the Orange Pi boards. This is a super rare situation though.
I love projects like this! Start with something super-accessible and turn it into something amazing! Nicely done!
This is a great update to something I’ve seen for decades. Thanks for sharing!
I just saw the cup concept on one of the science-y Instagram accounts I follow and was thinking it was cool but would be WAY cooler with FastLED 
I’ll have to try one soon