Captainbob, I presume you're planning on an ESC to run your motor and just need a means to provide the appropriate signal for it. You might be able to purchase and modify a servo tester (Amazon offers a few under 7 bucks) that includes a knob to adjust the output pulse width. If you can solder and build a simple circuit, Google "servo tester circuit" for several examples. In either case, you'll substitute resistors whose serial or parallel values are altered by your pressure switch to get the appropriate output pulse width. Program your ESC to run the appropriate speed at one pulse width and stop at the other. Good luck finding a pressure switch light/cheap enough to fit your weight and cost budget.