Machine Design

Along came a Spider mower

Lie in a hammock, sip ice-cold lemonade, and mow the lawn at the same time?

Spider remotecontrolled mowers make a 31.5-in. cut and handle inclines up to 40°. An electromagnetic Ogura PTO clutch/brake couples the engine to the cutting blades and slows blades to a stop when it is disengaged.

The Spider remote-controlled mower from DvorÁk Slope Mowers in the Czech Republic ( makes it possible. The 400-lb, 4WD mower is powered by a 17-hp Kawasaki gas engine and cuts a 31.5-in. swath, a width rivaling some commercial mowers. It can handle inclines to 40°, typically the job of manual weed whackers. Speed is variable up to 7 km/hr (forward or reverse) and is controlled by a hydraulic pump that drives four separate hydraulic motors, one per wheel. Hightorque electric motors do the steering.

Engine operation, speed, steering, deck height, and blade engage-ment/ disengagement are all controlled remotely. The control itself operates at 40 MHz and is similar to that used for model airplanes. Safety is of primary concern.

The unit automatically shuts down when the signal is lost or errant, if battery power is lost, or when the unit is out of range. An Ogura PTO electromagnetic clutch/brake from Ogura Industrial Corp., Somerset, N.J., (www. couples the engine to the cutting blades. When power is lost or the clutch is disengaged by the operator, the clutch armature springs pull back against the brake shroud, causing a mechanical drag which helps slow the blades to a stop.

The Ogura PTO clutch was chosen because it handles high torque levels and comes in a small package. The use of a double-flux armature and rotor design boosts torque by about 35% over singleflux types. Three nuts on the clutch adjust for wear between the armature and rotor and extend life of the unit.



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