How to Increase Velocity of a Servo motor, relative to resistance?

I am building a RC car which increase its speed to compensate any obstacle on its way.

A simple 4 wheel RC car, with current sensor on the two front wheels, when an obstacle is placed in front of the car, the car slows down if the obstacle is heavy and may stop if the obstacle is very heavy. my question is how can i take the input of the current sensor to increase the Motor's speed to try to compensate for the added obstacle.

• Your question title uses the words "servo motor". Are you sure that the car's drive is using servo motors. It seems unlikely. In any case, you probably mean "How to increase motor's power to maintain velocity at various loads" not increase it. – Transistor Apr 8 '18 at 13:12
• I was immediately thinking of a compound winding but I think they don't do those on RC car motors. – Oldfart Apr 8 '18 at 15:08

$$PI(s) = K_p + \frac{K_i}{s}$$