with reference to the drawings , the disclosure relates to a grinder 10 having a motor 12 mounted by a motor mount 12 a onto a drum assembly 14 , with one or more drive units 16 located on the exterior of the drum assembly 14 for rotation of the drum assembly 14 . a bearing assembly 18 interfaces between the motor mount 12 a and the drum assembly 14 to enable the drum assembly 14 to rotate relative to the motor 12 . the grinder 10 may be integrated with a frame or the like having handles and controls for facilitating operation of the grinder 10 . the motor 12 is typically an electric motor . the motor 12 may have various motor power ratings , typically ranging between about 5 and 25 horsepower . the motor 12 is fixedly mounted to the motor mount 12 a , and the motor mount 12 a is rotatably mounted to the drum assembly 14 by the bearing 18 . the motor 12 includes an output shaft 12 b that is preferably driven at a variable rotary speed of from about 350 to about 1 , 400 revolutions per minute . the drum assembly 14 includes a top plate 20 and circumferential sidewall 20 a , a drive pulley 22 , a drive belt 24 , a plurality of idler pulleys 26 a - 26 c , a plurality of driven pulleys 28 a - 28 d , a bottom plate 30 , and plurality of driven disks 32 a - 32 d . a belt tensioner 34 is mounted to the underside of the top plate 20 to desirably adjust the tension of the drive belt 24 . the motor 12 is mounted to the exterior of the top plate 20 by the motor mount 12 a . the output shaft 12 b of the motor 12 extends into the drum assembly 14 via an aperture 36 centrally located on the top plate 20 . the drive pulley 22 operatively engages the output shaft 12 b of the motor 12 so as to rotate corresponding to the rotation of the output shaft 12 b . the drive belt 24 travels around the idler pulleys 26 a - 26 c and the driven pulleys 28 a - 28 d and transfers rotation of the drive pulley to the driven pulleys 28 a - 28 d . together , the idler pulleys 26 a - 26 c and the belt tensioner 34 serve to provide desired tension of the drive belt 24 and contact of the drive belt 24 with the driven pulleys 28 a - 28 d . the drive belt 24 is the only traveling belt utilized on the grinder 10 . with reference to fig5 , it will be observed that the drive belt 24 is arranged to contact the driven pulleys 28 a and 28 d such that the driven pulleys 28 a and 28 c each rotate in the same direction and opposite to the direction of travel of the drive belt 24 , and the driven pulleys 28 b and 28 d each rotate in the same direction and in the same direction of travel of the drive belt 24 . thus , if the drive belt 24 travels counter - clockwise , the driven pulleys 28 a and 28 c each rotate clockwise and the driven pulleys 28 b and 28 d each rotate counter - clockwise . the driven pulleys 28 a - 28 d each include a downwardly extending shaft 38 that extends from the bottom of each of the driven pulleys 28 a - 28 d and passes through a corresponding aperture 40 of the bottom plate 30 . the driven disks 32 a - 32 d directly connect to the shafts 38 of the driven pulleys 28 a - 28 d adjacent the exterior surface of the bottom plate 30 , and rotate with the driven pulleys 28 a - 28 d . various work pieces , such as grinding disks and the like , may be connected to the driven disks 32 a - 32 d for treating a flooring surface . two of the driven pulleys , such as the driven pulleys 28 a and 28 c located opposite of one another , include upwardly extending shafts 42 that extend upwardly from the driven pulleys and extend through apertures 44 of the top plate . with additional reference to fig8 - 11 , the drive units 16 connect to and are driven by the upwardly extending shafts 42 of the driven pulleys 28 a and 28 c . in this regard , a gear pulley 46 is located on the shafts 46 to provide a rotary drive surface . alternatively , the shaft 42 itself could provide the drive surface , or the shaft could be coated with rubber or the like to provide a drive surface . as described herein , the gear pulley 46 provides the drive surface . each drive unit 16 includes an anchor plate 50 that mounts to the top plate 20 of the drum assembly 14 . the anchor plate 50 is connected by a spring loaded yoke system 52 to a pulley mount 54 . the drive units 16 are mounted onto the drum assembly 14 to drive the drum assembly in a direction opposite that of the rotation of the driven disks 32 a - 32 d . the anchor plate 50 may be an l - shaped metal plate having an aperture 50 a in for mounting of the anchor plate 50 to the top plate 20 as by use of a fastener . an upstanding portion of the anchor plate includes an aperture 50 b for mounting of the yoke system 52 to the anchor plate 50 . the yoke system 52 includes a yoke end 56 having a pair of arms 56 a and 56 b with aligned apertures for mounting of the yoke end 56 onto the pulley mount 54 . to enable some controlled lateral relative movement , a threaded bolt 58 adjustably connects to the yoke end 56 and a compression spring 60 is located on the bolt 58 opposite the yoke end 56 to bear against the anchor plate 50 . a compression spring 62 interfaces between the yoke end 56 and the pulley mount 54 for enabling controlled vertical movement of the pulley mount 54 relative to the yoke system 52 . the pulley mount 54 includes a frame 64 having an aperture 66 configured to receive the gear pulley 46 and configured to permit rotation of the gear pulley 46 as driven by the driven pulley 28 a or 28 c . the frame 64 is also configured to rotatably mount , preferably utilizing bearings or the like , a gear pulley 68 adjacent to and in frictional contact with the gear pulley 46 for being driven by the gear pulley 46 . in this regard , the gear pulley 46 and the gear pulley 68 may include surfaces configured to encourage frictional interaction , such as including rubberized surfaces and / or cooperating ridges 46 a and 68 a , respectively . the ridges 46 a and 68 a are shown partly around the circumference , it being understood that they may preferably extend around the circumference . as will be understood , the gear pulley 46 rotating in a first direction , such as clockwise , will impart a rotation to the gear pulley 68 in a second , opposite direction , such as counter - clockwise . the anchor plate 50 , yoke system 52 , and the pulley mount 54 cooperate to rotatably position the gear pulley 68 in contact with a circumferential surface 70 of the motor mount 12 a . the circumferential surface 70 is preferably coated with a rubber or like material to frictionally engage the gear pulley , yet enable some slippage if substantial counter - rotational forces are encountered . alternatively , a replaceable fixed ( non - traveling ) belt or band or sleeve or the like may be located around the circumferential surface 70 to contact the gear pulley 68 . in operation of the grinder 10 , it will be understood that rotation of the output shaft 12 b is transferred by the drive pulley 22 to cause the drive belt 24 to travel and transfer rotation to the driven pulleys 28 a - 28 d , causing rotation of the driven disks 32 a - 32 d in a first direction , such as clockwise . the clockwise rotation of the driven pulleys 28 a and 28 c provides clockwise rotation of the gear pulleys 46 mounted thereon , which transfers an opposite rotation of the gear pulleys 68 . thus , for example , clockwise rotation of the driven pulleys 28 a and 28 c provides clockwise rotation to the gear pulleys 46 . the clockwise rotation of the gear pulleys 46 imparts opposite or counter - clockwise rotation to the gear pulleys 68 . the gear pulleys 68 contact the circumferential surface 70 of the motor mount 12 b , imparting an opposite , clockwise motion to the drum assembly 14 . accordingly , in operation , rotation of the output shaft 12 b of the motor 12 is transferred by the traveling drive belt 24 . the drive belt 24 transfers its rotation to the driven pulleys 28 a - 28 d to cause the driven pulleys 28 a and 28 c to rotate opposite of the direction of travel of the belt 24 , and the cause the driven pulleys 28 b and 28 d to rotate in the same direction of travel as the drive belt 24 . the rotation of the driven pulleys 28 a and 28 c rotates the gear pulleys 46 mounted thereto . the gear pulleys 46 contact the gear pulleys 68 of the drive units 16 to cause the gear pulleys 68 to rotate opposite of the driven pulleys 28 a and 28 c . the gear pulleys 68 contact the circumferential surface 70 of the motor mount 12 a to cause the drum assembly 14 to rotate opposite the direction of rotation of the gear pulleys 68 and in the same direction as the driven pulleys 28 a and 28 c . the driven pulleys 28 b and 28 d rotate opposite of the drum assembly 14 and the driven pulleys 28 a and 28 c . the foregoing description of preferred embodiments for this disclosure have been presented for purposes of illustration and description . they are not intended to be exhaustive or to limit the disclosure to the precise form disclosed . obvious modifications or variations are possible in light of the above teachings . the embodiments are chosen and described in an effort to provide the best illustrations of the principles of the disclosure and its practical application , and to thereby enable one of ordinary skill in the art to utilize the disclosure in various embodiments and with various modifications as are suited to the particular use contemplated . all such modifications and variations are within the scope of the disclosure as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly , legally , and equitably entitled .
a drive unit for imparting rotation to a drum assembly of a floor grinder . the drive unit includes a rotatable pulley positioned adjacent to and in contact with a rotatable drive surface of a driven pulley of the drum assembly and a drive surface of the drum assembly . the rotatable drive surface of the driven pulley is configured to impart rotation to the rotatable drive pulley during rotation of the rotatable drive surface , and the rotatable drive pulley is configured to impart rotation thereof to the drum assembly .