The advanced generator (nuclear generator) from rampant arsenal weren't placeable in the spidertron-mk3. The following code in a tiny mod fixed it. A similar fix for the other spidertrons also is needed.

local grids = data.raw["equipment-grid"]["spidertronmk3-grid"].equipment_categories
if grids then
grids[#grids+1] = "adv-generator"
end

Sorry, was out of the city for the past week and just got home.
This rampant arsenal: https://mods.factorio.com/mod/RampantArsenal if yes i'll add compatibility file for it when i get more time from work.

https://cdn.discordapp.com/attachments/785820785871945738/839620679162396732/unknown.png
Already add a small change to make it work now, the info was very useful. The bad part is that i don't want to add the fix yet because i still have a bug when i was playing with some other code and need to fix it, hopefully this weekend going to release version 0.3.9 with this change and no big bugs. Sorry for the delay on it.

EDIT:
Just comited the changes on github for this:
If you really need the fix right now you can copy the files and add them in the mod directly
Open the mod at:
%appdata%\Roaming\Factorio\mods\spidertron-extended_0.3.8.zip
and replace the file:
https://github.com/stefanaonx/spidertron-extended/blob/master/data.lua
and add the file:
https://github.com/stefanaonx/spidertron-extended/blob/master/compatibility/rampantarsenal.lua
in the compatibility folder in the zip

Still going to add this change in 0.3.9 when i'll get more time to fix some stuff.

Sorry again for the delay, finally added 0.3.9 with the fix, tell me if you encounter any problems.