I am still in my father's old magazines, and I found this 50%/20% betting method on simple odds (black/red, even/odd, 1-18,19-36). It is a kind of less risky martingale because you don't double with each loss.
How to bet on the 50%/20% growth
After each loss you must increase the bet by 50%.
After each win you must reduce the bet by 20%.
Example to fully understand the 50%/20% method
Note here that with 3 losses and 2 gains, it is profitable
You can also test this roulette method with 30% in case of losses and -10% in case of winnings. The advantage is to take even less risk.
Conclusion on the 50%/20% method
This method will probably not make you rich and still involves some risk, it remains a martingale, less risky certainly, but if you are in a bad series you risk losing everything. You must set limits on gains and losses.
Also, if you have a small capital, this method is probably not for you. If you have a budget of 50 € or less, I advise you the method on 120 full numbers, with 50 cts bets. The advantage of the 120 method is that it does not make you play much for very interesting results. I play it in addition to other methods on Dublinbet.