scale comparison

Most mecha anime have preproduction art that gives the relative sizes of their mecha, so that the animators can try to keep the correct sizes. Super Dimensional Fortress Macross and Genesis Climber MOSPEADA both had their scale images made public.

Super Dimensional Fortress Macross

Genesis Climber MOSPEADA

using that preproduction art, i threw together a scale comparison between the mecha from the 3rd segment of the show (based on MOSPEADA) on the left and the 1st segment of the show (based on Macross) on the right. since the two images have different perspective angles, the comparison is only approximate, the VBF-9 Beta for example is actually a few feet taller than a VF-1 Valkyrie.
Click for full sized.

 While Super Dimension Cavalry Southern Cross has not had such an image found yet (or to be honest, much of any pre-production material  at all), I was able to piece together a quick and dirty scale guide for the Shadow Chronicles RPG using various artwork found online.
combined with the Macross and MOSPEADA artwork above, you have a guide to the scales of the Robotech mecha.

(click to see full size.)

also this one made by fans, illustrating the main transforming mecha of each generation in the show.: has a scale page available to members, though it does not have all the mecha. it has been a valuable second source of information for double checking the art above.
from left to right, Zentraedi Regult Battlepod, VF-1J Valkyrie Veritech, VHT-1 Spartas Hovertank, MK-1 Bioroid, VH/A-6 Alpha Veritech, Invid Iigaa Attack Scout