I'm building a powered towbar for moving an airplane. I have a 1/4HP Bodine 42D Brushed Gear Motor, 130VDC, 1.8A, Geared (60:1) to 42 RPM, 270 in-lb of Torque. I want to build a unidirectional PWM soft-start, speed-controller. Reversing will be done with a DPDT toggle switch, so the controller can be unipolar (not an H-Brdge), but should ramp the speed up for ~ 2sec after the trigger is pulled for a jerk-free start. This will be attached to the nose landing gear, so the smooth start is to protect against damaging that.
I have already chosen the sprockets for the final speed reduction in the chain drive to get the desired linear movement speed when the motor is running wide open, so the primary job of the PWM controller is to accelerate the motor slowly/smoothly.
I don't think I need a tacho-feedback-controlled speed controller, just a smooth ramp on initial start; I don't need dynamic braking either; I think I can just let the motor spin-down naturally when power is removed.
I can cobble up an opamp integrator to generate the speed-up profile ramp; an opamp to produce a sawtooth at the PWM freq, and a comparator to create the PWM signal. The area I could use some help with is finding an NFET for switching the current to the motor. I will be using a 130V DC supply, so I'm worried about selecting a high-voltage FET which will take the voltage and the dissipation.
Ideas welcome.
I have already chosen the sprockets for the final speed reduction in the chain drive to get the desired linear movement speed when the motor is running wide open, so the primary job of the PWM controller is to accelerate the motor slowly/smoothly.
I don't think I need a tacho-feedback-controlled speed controller, just a smooth ramp on initial start; I don't need dynamic braking either; I think I can just let the motor spin-down naturally when power is removed.
I can cobble up an opamp integrator to generate the speed-up profile ramp; an opamp to produce a sawtooth at the PWM freq, and a comparator to create the PWM signal. The area I could use some help with is finding an NFET for switching the current to the motor. I will be using a 130V DC supply, so I'm worried about selecting a high-voltage FET which will take the voltage and the dissipation.
Ideas welcome.
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