Motor clusters on Open Rocket?

[Senior Space Cadet]

One of my next builds is going to be a BT-80 with a three 24mm radial motor cluster.
I have some time today, so I was playing with it on Open Rocket.
I figured out how to do the motor tubes, but I'm having a problem with the centering rings and motors. It wants to put one 24mm hole in the middle and if I try to install a motor, it's only giving me 18mm choices, not 24mm.
Haven't even tried to put an engine block in. Not sure what it will do with that. I like to, at least, make sure the CG is in the right ball park before starting to build. I generally make sure I err on the side of stability.

 

[Nytrunner]

See if "Limit choices to mount diameter" is checked in the motor selection window. If your motor tubes are slightly small, the program will limit you to the lower size unless you uncheck that box,

The centering ring graphic will only display one hole, but Iif you go to File and Print the centering ring templates, they'll show the correct cluster pattern

 

[dhbarr]

After you create & position your cluster, split it and upsize the center core.

 

[Jay Rairigh]

Are the 3 inner tubes set up to be motor mounts?