Minimum Ogauge radius?

[StuartM]

I'm toying with the idea of making a wall mounted O gauge shelf layout that runs around the top of my room in a continuous loop,

possibly a double loop about 18" from the ceiling.

Making a shelf that runs along the straight walls is easy enough, but the 4 corners will be more challenging.

Does anyone know the minimum radius that a co-co O gauge loco can reliably negotiate considering that there maybe an inner and outer loop.

[spamcan61]

Discussion here suggests 3 foot odd:-

 

https://www.rmweb.co.uk/community/index.php?/topic/137750-what-can-i-get-around-a-33-curve/&do=findComment&comment=3309503