[darksaints]

He actually used steel cables for his initial prototypes, but steel cables have a problem with rolling fatigue that actually gets worse the larger the diameter...so if a tiny steel cable is not strong enough, you might actually have to change the gear dimensions (and therefore ratios) in order to not fatigue them.

[Animats]

Right. Steel cables have to be oiled internally if flexed frequently. This was a major cause of cable failure in gym exercise machines for decades. Newer exercise machines tend to use synthetic flat straps over pulleys.

[kragen]

The Sandia paper also claimed that steel cables need a larger pulley radius.