We burned through all of our investors' money, and worked until we couldn't meet payroll. Once it was clear that we were going to run out of cash, I took a job and negotiated a deal that allowed me to make our investors whole.
If you chose to do it of your own volition, then that's a personal decision (though one I don't recommend because your investors made a calculated wager on you...sometimes wagers lose, and that's the nature of the game they have chosen to play). But if you were asked or pressured into it, they shouldn't have done that, and by doing it voluntarily, you are teaching those investors to expect it of others.
I'm curious if you feel it could have worked out differently if you'd flipped the approach on its head and instead of starting with investment and then the product, you bootstrapped custom radios and built the platform out from there when you had some traction?
I ask partially because I'm in a similar place at the moment with a product (http://mirobot.io) and considering different growth strategies.