If you want a hardware upgrade it's actually reasonably inexpensive to build something direct drive (which is how the real sub-30kg ones work). This gives you many advantages over the plastic gear type including a much faster response time and more accurate positioning.
Look for "gimbal motors", basically a large skinny pancake brushless motor. Combine those with a storm32, simplebgc or odrive and a magnetic encoder. A 3D printer will help.
You can also have a look at low cost suppliers of cheap UAV stuff if you want something fully integrated for you. A basic Gremsy, Viewpro or Siyi isn't that much more than your Amazon thing. Various software bugs but they can be worked around. The DJI units can sometimes be had used and some of the protocols have been RE'd already.
Presumably also open circuit not rebreather given this was mid 90s. It's a pity the article doesn't detail their dive plan, the gas quantities must have been staggering.
Nowadays this type of diving would be done using an eCCR (and backup open circuit), where some software on a microcontroller controls the amount of oxygen in a breathing loop. A scrubber (hopefully) removes the CO2. Changing the gas mixture as you go is required to reach these sorts of depths because oxygen becomes toxic at pressure, and gas density itself can cause issues with breathing.
If you want a hardware upgrade it's actually reasonably inexpensive to build something direct drive (which is how the real sub-30kg ones work). This gives you many advantages over the plastic gear type including a much faster response time and more accurate positioning.
Look for "gimbal motors", basically a large skinny pancake brushless motor. Combine those with a storm32, simplebgc or odrive and a magnetic encoder. A 3D printer will help.
You can also have a look at low cost suppliers of cheap UAV stuff if you want something fully integrated for you. A basic Gremsy, Viewpro or Siyi isn't that much more than your Amazon thing. Various software bugs but they can be worked around. The DJI units can sometimes be had used and some of the protocols have been RE'd already.