I just got my first epic chest from battle and I am in arena 7. Although I did get my epic chest, I didn't get a legendary chest before the epic, and I have never obtained the legendary chest from battle. Since I just got the epic chest, will I get a legendary chest in the next battle and/or sometime soon? I have also been waiting for a long time to get the legendary chest.
How do the Chests drop? It’s based on the Clash Royale Chest Cycle!
Basically there is a chest order (or chest cycle) in game. Every Chest that you get after the Battles is based on this list. When this cycle goes through, it will restart again. By digging the game files, Asdamp (Pearce) has found this chest order list.
You will always get 6 Wooden Chests at first, during the Training Camp. This is the latest pattern, updated on 30th December 2016.
What about the Legendary Chest?
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You have the chance to get this chest once you hit 2000 trophies. Below Arena 9, you are guaranteed a Legendary Chest in every 2 cycles (yes, the circle above).
In Arena 9, you are guaranteed a Legendary Ches in every chest cycle. This chest randomly replaces a chest in the Clash Royale Chest Cycle.
If you bounce between Arenas, your Legendary chest drop rate is still one per 2 cycles. You need to stay in Arena 9 during the entire cycle to get one chest every cycle.
This information was from: http://clashroyalearena.com/tips/how-does-the-chest-drop
Legendary and Epic chest odds are independent of one another. You are not guaranteed a legendary chest. There is no way of telling when your legendary chest will drop, but if you are near the end of the cycle, you may be getting one soon.
Orange Juice Gaming has an excellent video on chest odds.