That sounds like the reverse of Shu!, one of my Beetleweights where it had a long arm on the front and was capable of pretty much dislodging itself from anything as the arm could go though near 180. Here is a video of it in action.



I used a planetary gear gearbox in that but I reckon a simple enough spur gear arrangement with a pair of heavy duty chain and sprockets as the final stage would work (I had considered and even CADed up a HW version of Shu!) I think the key is getting a low enough RPM motor that can be further reduced down significantly for that extra torque.