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Acceleration and Deceleration Ramps

Acceleration and deceleration ramps are a valuable part of the function of a motor speed controller. Without a controller if you connect a battery directly to a motor there will be a sudden surge of torque as the motor instantly tries to accelerate to its top speed. We have seen this torque surge be strong enough to tear the motor off its mountings.

When a controller is fitted, this sudden surge does not occur as the motor speed controller winds the motor up at a controlled rate. The ‘winding up’ of the speed is not only done by the operator slowly turning up the demand motor speed control, but there is also a wind-up rate built into the controller, so even if the rider turns up the demand speed suddenly, the controller will still wind up the motor at a more sedate rate. This ‘winding up rate’ is called an ‘acceleration ramp’. There is also in the controller a ‘deceleration ramp’ (which may or may not be independent of the acceleration ramp) to control the winding down.

examples of acceleration and deceleration ramp curves

The easiest ramp to put into a circuit is a simple C-R ramp (so called because it is done by means of a capacitor charging up through a resistor). A better ramp is a ‘linear’ ramp. The diagram shows the two.

At point A the demand speed control is suddenly turned to full speed. Initially the motor speed starts increasing fast. However as it gets faster, its rate of speed increase slows and as it reaches full speed the rate is quite slow. At point B, the demand speed is suddenly reduced to zero. With the CR ramp the speed reduces quickly at first but the deceleration decreases as the motor slows down so that the speed finally fades slowly to nothing.

The second curve shows the effect of the more sophisticated linear ramp. Here the acceleration and deceleration rates are constant throughout, with no ‘fading’.

All 4QD controllers now use the linear ramp model, and both the acceleration and deceleration rates can be adjusted independently. If the standard times are too short we can change them for special orders.