[FrankJ]

The 8-10% number is a general number that comes from the people who make the poly cord installed in its intended application. It gives tension required to allow the rollers to transmit torque. When used as a conveyor it gives reasonable deflection when pushed in a reasonable way. Little a first robot does is reasonable.

If you are able to get the results you want with a lower stretch, go for it. Higher stretch than recommend will eventually result in failure. Maybe long after the season is over.