Hi @model14,
Sounds like an interesting project! 
In case it’s of interest, there’s a similar system that was brought up recently here
I expect that spinning and rolling propulsion mechanisms are in general poorly suited to gradual vertical density changes in the medium being moved through:
- propellers pull up denser material from below which can make them slow down and/or get stuck while also reducing visibility
- small wheels have little to grip onto, and large wheels are heavy, bulky, and may have similar issues to propellers
Likely a more effective solution would be an undulating, gliding, and/or flapping mechanism (e.g. something like this biomimetic robot). Unfortunately such mechanisms don’t tend to be readily available, or have readily available control algorithms, so making one would likely need a fair amount of custom development of both hardware and software (although it’d also be really cool…).
Glad to hear it, and good to have you back