Excavator

Ok, super half baked, but what the hell.

Drop

The digger consists of two sharp steel plates with a slight bend to them - like the head of a shovel only a bit wider. The curve is also a lot shallower. The two halves come together and over lap just as far as that curve. The whole thing is hoisted into the air and dropped, the weight of the mechanism driving it into the ground. The hoist mechanism and the weights works together to push the jaws closed. The whole thing operates on two sliding rails so it can be moved over a bucket and unloaded.

Bike

Digs a long straight, wide trench. 4 wheels, no steering. Right behind the front wheels is a set of spinning blades like a tiller. Behind that is a ramp and behind that is the bucket. Then the back wheels. Front wheels are 1ft higher than everything else. They ride on top of what is about to be dug.

Pedaling spins the blades. A very high reduction can also transfer that from the blade to the back wheels. To use it, you'd have to manually dig out an area to set it down. Then start pedaling to get the tiller up to speed, then engage the wheels.

Ideally, the back section would be a square so that I could dig a starter, then use it to dig a trench, then go perpendicular to the trench.