Extendable vehicle step and step motor control system

A positionable step for vehicles, said step comprising,

• a base adapted for attachment to the vehicle,
• a step extensible from a stowed position beneath the base to an extended position whereat the step is downwardly and outwardly offset from the vehicle,
• step support members swingably postionable from a stowed position beneath the base,
• cooperating means carried by said step and said support members and slidably supporting the step for lengthwise travel along said support members during step extension and retraction,
• front and rear pairs of links coupling said step support members and said step to the base so as to permit swinging movement of the step and step support members, said rear pair of links each including lowermost arm portions imparting sliding motion to said step for travel lengthwise along said support members, and
• step actuating means carried by said base including a reversible electric motor in driving connection with the rear pair of links and a motor control system operable to determine fixed intervals of motor operation constituting step extension and retraction regardless of stalling of the motor by a step obstruction, said motor control system includes semiconductor controlled rectifiers, one of said rectifiers having its cathode in a switch controlled circuit with said motor, capacitor means in circuit with said cathode of said one rectifier, said capacitor means discharging after a predetermined period to momentarily change the charge on said cathode to a negative charge thereby terminating said one rectifier operation to open said circuit to the motor after the predetermined period.