i'm toying around with the same idea, but i haven't decided yet on a sliding vs hinged door. i slider takes us less depth and is perhaps simpler but even when fully open it still blocks the grill for about 50 %.
interestingly yesterday i spotted an automatic grillblock "in the wild" it was a factory installed setup on a bwm 1 series hatchback, i think it was the vavorable light as the block sat quite deep.
it was some sort of "windowblinds" like setup with individually hinged vanes that where shaped to interlock and form a complete internal grillblock behind the topgrill
for now i'm leaning towards a single or multiple hinged door design, opperated by tow strings and a pulley connected to a single electric motor...
one string winds up while the other unwinds. this was there will be some restriction to the door movement when the motor is off so it doesn't flutter about, but also it's the simplest way to convert rotary motion into a 2dimentional movement, and have a reduction at the same time without the need for precise gears.
i hope to build a working off-car prototype over the next weeks, but several issues and parts need to be located so we'll see
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