fig1 and 2 illustrate one embodiment of the present invention . a brush cutter attachment 10 is shown attached to the front of a cab 50 . the brush cutter attachment 10 may be used to cut brush such as plants , grass , weeds , branches and the like . the cab 50 provides means for an operator to steer and advance the brush cutter attachment 10 over a surface to be cleared by the attachment 10 . the brush cutter attachment 10 is shown as having a housing 20 and a side panel 30 moveably secured to the housing 20 in a pivotal fashion . a biasing assembly 40 extends from the housing 20 to the side panel 30 urging the side panel 30 downwardly with respect to the housing 20 . the attachment 10 is operated by a motor . a shut - off valve 42 is mounted to the housing 20 and is activated to shut off the motor when the side panel 30 extends downwardly a predetermined distance with respect to the housing 20 . as shown in fig1 , the side panel 30 is biased to contact the cutting surface as the housing 20 travels over the surface . in this illustration , operation of the shut - off 42 valve will not occur and the motor will continue to operate . as shown in fig2 , the housing 20 may be movable a predetermined distance above the surface to be cleared . this will render the side panel 30 extending downwardly a predetermined distance relative to the housing 20 , thus initiating the shut - off valve 42 and shutting off the motor . the housing 20 has a pair of sidewalls 22 , a front wall 24 , a rear wall 26 , and a cover 28 , for housing a cutting blade . the cutting blade rotates about a shaft extending through the cover 28 toward the cutting surface . the blade rotates , it is intended , substantially parallel to the cutting surface at a predetermined height above that surface . the cutting blade is rotated by the motor . the motor is mounted on a top portion of the housing cover 28 , within a motor casing . the side panel 30 is moveably secured to the housing 20 . the side panel 20 is biased downwardly with respect to the housing 20 for preventing debris from projecting from beneath the housing 20 and possibly causing injury to the operator or to a bystander . the side panel may 30 extend along the entire fore - and - aft length of the brush cutter 10 . the side panel 30 is , at a front location 32 , pivotally connected to the housing 20 . the front portion 32 has an aperture 34 for pivotally securing the side panel 30 to the housing 20 . a locking bolt 36 may be extended through the aperture 34 to maintain the side panel 30 adjacent the housing 20 . a neck 37 of the bolt 36 may extend through the aperture 34 and into a securing portion of the housing 20 . the head of the bolt 36 may extend to an outer surface 31 of the side panel 30 for maintaining the side panel 30 adjacent to the housing 20 . the side panel 30 has a back portion 38 that pivots about the aperture 34 . the back portion 38 has an arcuate slot 39 for receiving a guide member 35 . the guide member 35 extends from the housing 20 and through the slot 39 . the guide member 35 may have a head that extends through to an outer side 31 of the side panel 30 . the head portion may be wider than the slot 39 to maintain the side panel 30 adjacent the housing 20 . the slot 39 may have a radius of curvature for allowing the side panel 30 to pivot . the side panel 30 is able to pivot about the locking bolt 36 until the guide member 35 contacts an upper limit or lower limit of the slot 39 . the panel 30 has a top side 52 and a bottom side 54 . the top side 52 may converge toward the bottom side 54 as it progresses toward the front 32 of the side panel 30 . a substantial length of the bottom side 54 of the side panel 30 is linear for contacting the cutting surface . in operation , as the brush cutter 10 is advanced over a surface , the side panel can pivot about the locking bolt 36 . for example , if the housing 20 is substantially close to the cutting surface , the side panel 30 will be centered such that the guide member 35 is spaced from the upper limit 56 and lower limit 58 of the slot 39 . if the housing 20 becomes raised above the cutting surface , the side panel 30 moves downwardly toward the cutting surface such that the guide member 35 becomes located at the upper limit 56 of the slot 39 and the bottom side 54 of the side panel 20 extends below a lower portion 21 of the housing 20 . the housing 20 has a cover panel 28 and a pair of sidewalls 22 for housing the cutting blade . the housing 20 has a front portion 25 that is angled upwardly with respect to the lower portion 21 of the housing 20 . the front portion 25 allows for brush to be received within the housing 20 in order to be cut by the blades . the housing 20 has a rear portion 27 for connection to the cab 50 . by connecting to the cab 50 , the housing 20 may be directed over the cutting surface by the operator of the cab 50 . a motor used for rotating the blade may also be connected to , and operable from , the cab 50 . the motor provides a torque force to a blade shaft for rotating the blade . fig3 through 6 illustrate a biasing mechanism 40 mounted for biasing the side panel 30 downwardly with respect to the housing 20 . a shut - off valve 42 is also secured to the housing 20 . the shut - off valve 42 works in tandem with the biasing mechanism 40 such that , when the side panel 30 is fully extended downwardly , the shut - off valve 42 will be switched so as to shut - off the motor to the rotatable blade , thus stopping the blade from being rotated and preventing possible injury to the operator . turning now to fig3 - 6 , the biasing mechanism 40 includes a cylinder 44 and piston 46 assembly secured to the top portion 28 of the housing 20 . the cylinder 44 and piston 46 assembly may be hydraulic , as shown . the piston 46 has a working end 47 pivotally connected to a first end 62 of a bell crank 60 . a second end 64 of the bell crank 60 is pivotally attached to the side panel 30 via a connecting arm 66 . the connecting arm 66 has a first end 67 pivotally connected to the second end 64 of the bell crank 60 and a second end 68 pivotally connected to the side panel 30 . the bell crank 60 has an elbow 61 that is pivotally secured to the housing 20 . as shown , the elbow 61 is pivotally connected to a mounting member 29 extending from the top portion 28 of the housing 20 . the elbow 61 is positioned proximate the shut - off valve 42 . the shut - off valve 42 is secured to a motor casing 23 extending above a top portion 28 of the housing 20 . the shut - off valve 42 has a rotatable shaft 70 extending in a direction toward the side panel 30 . the shaft 70 has a first end 71 for receiving a pin 33 extending from the side panel 30 . a yoke 72 is positioned at the first end 71 for engaging the pin 33 such that , as the pin 33 is received within the yoke 72 , the shaft 70 will be rotated so as to initiate action by the shut - off valve 42 and shut - off the motor by shutting off the hydraulics to the motor . the shaft 70 has a lift limit switch 74 that will rotate with the shaft 70 such that , when the shaft 70 is rotated , the limit switch 74 will extend upwardly . the shut - off valve 42 may have a timer such that the valve 42 may be rotated for a predetermined period of time before the shut - off valve 42 initiates shutting down the motor . thus , if the yoke 72 is removed from a position receiving the pin 33 prior to reaching the predetermined period of time , the motor will not be shut off . the side panel 30 has a bracket 53 for mounting the pin 33 to the side panel 30 . the pin 33 extends inwardly from the side panel 30 for engaging the first end 71 of the shaft 70 . more specifically , the pin 33 extends from an inner portion of the side panel 30 for engaging the receiving portion 73 of the yoke 72 . the bracket 53 may be adjustable such that the height at which the housing 20 must be raised with respect to the side panel 30 at which the shut - off valve 42 will be engaged , may be adjusted . in operation , the motor will rotate the blade and the operator may steer the cab 50 over a cutting surface . as the brush cutter 10 travels over the cutting surface , the piston 46 is biased in the direction of the cylinder 44 , thus biasing the side panel 30 downwardly with respect to the housing 20 and towards the cutting surface . the elbow 61 will pivot so as to distend the connecting arm 66 downwardly toward the cutting surface . the side panel 30 is able to pivot about the front portion 32 locking bolt 36 and move upwardly and downwardly with respect to the housing 20 as the brush cutter 10 moves over ground . when the housing 20 is lifted a predetermined distance above the cutting surface , the side panel 30 will extend downwardly such that the engaging pin 33 will engage the yoke 72 at the first end 71 of the shaft 70 of the shut - off valve 42 . the engaged yoke 72 will cause the shaft 70 to rotate , initiating the shut - off valve 42 to shut - off the hydraulics to the motor , and thus shutting down the blade from rotating . the lift limit switch 74 extends upwardly from the housing . the operator may restart the motor by returning the brush cutter 10 to a height above the cutting surface that does not initiate the shut - off valve 42 . it will be understood that this disclosure , in many respects , is only illustrative . changes may be made in details , particularly in matters of shape , size , material , and arrangement of parts without exceeding the scope of the invention . accordingly , the scope of the invention is as defined in the language of the appended claims .
a safety apparatus for a tool driven by a motor removes motor power under certain circumstances . the tool includes a housing moveable over a ground surface for mounting the tool , and a ground - engaging member moveable relative to the housing and disposed to follow the ground surface as the housing moves over same . the apparatus further includes a sensor for measuring the relative position of the housing relative to the ground engaging member . motor control apparatus selectively stops the motor upon the ground - engaging member and the housing reaching a predetermined relative position .