[ms_menardi]

I had this idea for a "drill" that I'd like to make someday.

Basically it was a box with several tentacles snaking out of it. The tentacles would each have a drill on the end, and they would dig holes in a surface. These holes would be spaced apart and they would be on the outer edge of where the tunnel is meant to be. The silicon arms would be full of actuators that measured their resistance in terms of the momentum they want plus the gravity weight of any nodes after them.

After drilling around the surface, they'd turn (hence tentacles) and tunnel inward. Then, a big hammer or other impact would hit the main surface (after ensuring there were no tentacles below) and the shock of the impact would significantly reduce the amount of rock to carve through.

I really want to know why this wouldn't work, but I'm a designer, not an engineer, and I don't feel like making products. gee I sure wish I knew a bunch of engineers who would make this for me or at least tell me why it wouldn't work so I could use it sometime. Oh sorry for wanting there to be tunnels in every city on earth so we didn't have to destroy woodland to build suburban cities at such a gorgeous rate, I'm just a forest witch who doesn't fit in with startup founders and product engineers. gee wish there was a market fit for me.

"we don't have to dig through the rocks, just dig around the big ones and let them fall free" every digger knows this

[krisoft]

One thing is that “underground” is not a homogenous single thing. Sometimes it is loose water logged sand, or clay, or gravel, sometimes it is solid hard rock, sometimes it is large very hard pieces of fractured hard rock forming a loose rubble. Which kind of obstacle are you thinking when you are thinking of your method of digging? Based on your method description it sounds like you are thinking of loose soil with a few big rocks?

> The silicon arms would be full of actuators that measured their resistance in terms of the momentum they want plus the gravity weight of any nodes after them.

That sounds very complicated. Actuators are expensive. Actuators which are strong enough to drill through stone are even more so. Having many of them per arm and many arms per machine sounds very expensive and also a maintenance nightmare. Look at a real world tunnel boring machine: they have a cutting head rotated around by a single electric motor and hydraulic jacks to keep the cutting head pressed against the formation. It is conceptually simple, even though of course real world constraints make it complicated in practice. You are proposing to replace that conceptual simplicity with something much much more complicated. It is not clear what benefit you are hoping to achieve with the complexity you are thinking of.

> tunnels in every city on earth so we didn't have to destroy woodland to build suburban cities at such a gorgeous rate

How would that work in practice? Would people live in tunnels under a pristine forests? I’m not sure i understand your concept.

[senordevnyc]

I’m having trouble picturing this, I think. Maybe this will help: after this big hammer hits the rock with the outline of drilled holes around it…where do you think the rock goes? It’s not hollow under there…

[squibonpig]

I figure a big issue is you still need to move all of that displaced rock and earth out of the way