I am a newbie to embedded systems design so this question might seem very fundamental in nature.
I have been working as part of an Avionics team to develop an on board computing device for a unmanned aerial vehicle which would need to interact with various subsystems like camera, ir sensors, actuators, etc. We will be using a customized board design for this purpose, the cost of which comes to approx. 200k INR. Someone at work proposed why not use the chip inside a general purpose computer for the purpose or even a smartphone. The computer would cost between 50-60k while a smartphone would cost 20k which is cheaper than a customized board design. The idea seems ridiculous because of obvious reasons.
Firstly, the power consumption for a laptop board would be far more than any electronic board. But the same can't be said for a smartphone.
Secondly, an onboard computing device will require much more interfaces than a general computer/smartphone would provide.
The electronic board can be interacted with using several development kits like Vivado which I don't believe is possible in PCs/phones without an OS. I am not sure about this point.
Lastly, any smartphone/pc will be prone to bugs by design. We generally see laptops crashing and phones not reacting to touch commands which we can't afford in a real time based system like an unmanned aerial vehicle.
I gave the above arguments but none seem to be compelling enough to make someone of a non technical background understand this point. Is there an obvious/compelling reason which would prove the validity of my points to someone who doesn't have technical knowledge and is only concerned about bringing down the costs?
Edit: The unmanned vehicle needs to be mil-grade precise in our application, so it will need to handle a good amount of data efficiently that too in real-time while interacting with various sensors like camera, ir sensors, etc.