No you don't need a speed controller. All you need is the receiver and the servos to operate rudder and whatever functions you need for the steam plant. Plus a small battery pack to power all of these. I used a 4 x AA holder (6V in total) which did the job. Just make sure you buy one with the correct connector for plugging into your receiver. Plug all the servos and the battery pack into the receiver and away you go. You might also want a switch in the +ve line from the battery pack to save plugging and unplugging from the receiver every time, but that's about it.
Greg