As we all know its better to do some math before we start betting.
In general we can say that a rule can be multiplier x 15 should be more or less safe.
In case of 2x win this should be 2x15=30 that are the reds we can handle.
Next step is to calculate the base bet and dont underestimate the martingale power.
In order to survive 30 reds on 2x with a base of 0.00000001 we need a balance of 0.79btc, this is with a increase of 100% on loss.
If this article is going to be appriciated i will do some more complex examples.