In many building games the player's creativity is limited to a certain amount of blocks/parts that they can combine in different ways. That can be a lot of fun of course, but if you are looking for a game where designing mechanics from the scratch really is possible, you don't have too many choices.
From the beginning we wanted to keep the building mode as free as possible. On the other hand we didn't want dozens of pre-made parts that the player needs to browse through again and again. Basically that means our building mode has to be simple but versatile. We have seen that it's possible to make it that way if the few parts are well designed. We are planning to keep the number of parts less than 15. We'll see if that works when we start to get feedback from test players.
Right now we are working with these parts:
Metal frame - The primary material for creating structures. It's quite heavy but durable (but can be ruptured under stress/collisions).
Rod frame - Another structural material. It's much lighter than the metal frame. It always has freely rotating joints, which can come in handy sometimes. By connecting rods in a certain way it's also possible to create fixed structures.
Motor wheel - useful basic part when you need to get moving. Every wheel has its own electric motor in it. Wheels can be attached to the metal frame or to the axle.
Axle - Axles are for when you need to turn something. It always has to be mounted through a metal frame. Every part you mount to the axle rotates freely on the axis of the axle.
Bearing/joint - Sometimes the axle takes too much space to make a simple joint. With the bearing it's possible to make the joint of two metal frames turn. Sometimes the structure is more stable when using bearings instead of axles.
Motors - We are still trying to figure out the correct amount of motors. Hopefully we can manage everything with 2 or 3 motors but we'll see. The needs are different when making a steering system or walking mechanics, for example. Currently we are working with 2 motor types and it seems to work pretty well.
Hydraulic pump - Every real work machine needs hydraulics. These pumps can be as long as needed. The player can also adjust the initial starting position of the pump (i.e. fully extended - fully contracted). The pumps rotate freely, so you have to make your mechanics structurally sound by other means when using them.
Springs - Springs are of course essential when creating suspension systems. Like pumps, springs also rotate freely.
As a starting point there's always the rover hub which includes a battery. Every part has to be linked to the hub to have power. (it doesn't have to be a straight link, and all of the different parts act as links)
I'm sure we only have a hunch of what people can build with these parts. It's been a pleasure to try building different kinds of machines. We have tried diggers, trucks, monsters, cranes, loaders, mobile bridges, walking robots ect. It's super exciting to see what you guys can build when we get the first version out!