With the DP_SV_ROTATINGBMODEL QuakeC extension, brush entities can be made to rotate using the .avelocity field. The brush entity must have an "origin brush" or else it will rotate around the map origin.

To create an origin brush, create another brush in your level editor of choice and make it a part of the entity. The center of the new brush should be where you want the entity to rotate from. The new brush should also have an "ORIGIN" texture on it, so the map compiler can properly mark it as the center of that entity. In Q1-based games, this is usually just a texture named "ORIGIN" with no other special properties. In Q2-based games, it will be a texture with the "ORIGIN" contents flag set.

Finally, it needs some extra additions in QuakeC. In your entities .think function, assign the .avelocity field to a vector representing the rotation, in degrees per second.

Example Code

Here is an extremely basic func_rotate implementation in QuakeC for FTE:

enumflags {
	FUNC_ROTATE_X_AXIS,
	FUNC_ROTATE_Y_AXIS,
	FUNC_ROTATE_Z_AXIS
};

void func_rotate_think()
{
	// do rotations
	if (self.spawnflags & FUNC_ROTATE_X_AXIS)
		self.avelocity.x = self.speed;
	if (self.spawnflags & FUNC_ROTATE_Y_AXIS)
		self.avelocity.y = self.speed;
	if (self.spawnflags & FUNC_ROTATE_Z_AXIS)
		self.avelocity.z = self.speed;

	self.nextthink = self.ltime + 0.1;
}

void func_rotate()
{
	// setup brush model
	setorigin(self, self.origin);
	setmodel(self, self.model);
	self.movetype = MOVETYPE_PUSH;
	self.solid = SOLID_BSP;

	// start thinking
	self.think = func_rotate_think;
	self.nextthink = self.ltime + 0.1;
}