Good for the classics! They go beyond the outskirts, to protected places — boundless expanses, tall grasses, fresh breeze. Everything sets a poetic mood. And so it’s born: “Mow, scythe, while the dew…”, “Spread out, shoulder, swing, arm…”
But the ordinary modern “urbanized” villager (and the city dweller — owner of a small plot of land near a dacha) sometimes has no time for the sublime. Mowing and trimming grass often has to be done in places where, as they say, you can’t really get going with either a manual or any mechanical scythe. For example, when processing a garden planted with trees and shrubs, or a flower bed.
Homemade designs can help, where the working organ is a knife-cutter rotating at high speed in a horizontal plane. The magazine “Modelist-Konstruktor” has already told its readers and subscribers about some of them (see, for example, No. 5’85, 6’85, 4’90). The originality and reliability of these machines are duly appreciated by specialists, as well as by those DIY enthusiasts who have already acquired rotary mowers. We hope that no less interest will be shown in the published development.
The proposed homemade electric mower is designed for work in places with inconvenient or tight access. On small plots located within a radius of 30—50 m from the power source (AC network with 220 V voltage). And its design is such that it is quite accessible for independent manufacture even by beginners. After all, at its core is a fairly widely used 50-watt electric motor (from the “Veterok-3” vacuum cleaner). The only lathe part is the head in the drive unit. And everything else can be purchased in hardware stores or borrowed from old, worn-out household items — from duralumin baking sheets to the “Lentyayka” rag holder and transformer from the veteran KVN-49 TV.
The layout of the “electric mower” is simple: an electric motor is attached to the base, firmly clamped between the main and removable housing walls, with a cutting working organ (knife) at the end of the shaft. The required stubble height, prevention of touching the ground or bumps, and relatively easy movement are ensured by adjusting the height of the central and two side skids. The operator sets the direction of movement — through a handle hinged to the base.
For greater safety, as well as to create an optimal operating mode for the electric motor, the mower is powered through an isolation transformer with a semiconductor full-wave rectifier (bridge) in the secondary winding. Moreover, this unit is made as a separate block, easily connectable with all other parts of the structure.
And now about other features of the homemade electric mower. And first of all about the base. Cut from a 3-mm sheet of aluminum alloy AK4-1, it not only carries the drive with the knife, but at the same time is part of the cutting apparatus. Thanks to the “angle” guides and its radial configuration, the base ensures the formation of grass bundles, their feeding under the knife with subsequent movement of the mowed mass to the side.
Unlike industrial lawn mowers, in the proposed design the mowed mass is not cut multiple times, increasing the load on the knife and electric motor, but moves in a directed flow.
Grass is cut right at the ground. But if desired, you can mow from the tops, gradually lowering the base to the roots. This is done when they want to thoroughly chop the grass (for example, when decoratively trimming lawns).
1 — side skid (St3, rod with M5 thread and nuts on ends, 2 pcs.); 2 — knife (steel U7A, hardened to HRC 50…55, blued); 3 — short guide (aluminum angle 15×15, 9 pcs.); 4 — base (AK4-1, sheet s3); 5 — central skid (St3, rod with M5 thread and nuts on ends); 6 — electric drive unit assembly; 7,15 — electrical outlets; 8 — clamp (AMts, sheet s2); 9,14 — two-core wires in polyvinyl chloride insulation; 10 — spacer (aluminum angle 15×15); 11 — electric switch; 12 — thread bandage; 13 — fuse block; 16 — power supply unit housing; 17 — wooden handle (fastening — steel stud M5); 18 — electric cord with plug; 19 — handle (from “Lentyayka” rag clamp); 20 — bracket (St3, 2 pcs.); 21 — stud M4x170; 22 — nut M4 (4 pcs.); 23 — long guide (aluminum angle 15×15); 24 — textolite mounting board (with D226D diodes and 0.5 A fuses); 25 — transformer; 26 — tie bracket (AMts, 2 pcs.)
The electric drive unit consists, as already emphasized, of an electric motor clamped between shaped housing walls, which together with brackets made of aluminum alloy create reliable fastening, required rigidity, and well remove heat from the stator heating during operation. The electric motor is firmly fixed in the required position using protrusions on the stator (2 mm on each side), which enter into structural windows in the housing walls and are glued from the inside (to protect the brush assemblies from contact with the housing metal) with pieces of varnished cloth.
A head (the only lathe part) is fitted on the lower end of the electric motor shaft, on which a fan impeller is attached on top, and the mower knife on the bottom. Air for additional cooling is drawn in through the gap between the cover and walls. The air flow goes from top to bottom, also preventing dust from the soil from getting on the mower’s critical parts.
Rigidity of knife fixation on the head is achieved using a pressure disk and two screws with split washers, as well as thanks to careful balancing, for which a special 4 mm diameter hole is provided. By inserting a pin there, you can check the balance of the arms. Imbalance is eliminated by removing excess mass from the knife on a grinding wheel.
Power to the electric motor is supplied through a damper-insulator made from a PVC tube segment, protecting the electric cord from chafing at the passage point through the housing wall, and two thread bandages. Similar bandages, by the way, are also on the mower handle. Their winding is done in two layers with subsequent gluing with BF-6. A slightly modified “Lentyayka” rag clamp serves as the handle.
The power supply unit is made as a separate compact device. In the secondary winding of the isolation transformer — a rectifier on D226D type diodes. Connected to a single-phase network with 220 V voltage, the unit outputs direct (more precisely — pulsating) current to the mower’s electric motor, ensuring an optimal drive operating mode, in which sparking in the collector circuit is reduced, the probability of overheating of this unit is reduced, and therefore the operational reliability of the mower increases.
1 — knife; 2 — head (steel 45); 3 — fan impeller (St3, sheet s0,3); 4 — long guide; 5 — bolt M4 (8 pcs.); 6 — nut M4 (16 pcs.); 7 — base; 8 — main bracket (AMts, sheet s1,5); 9 — electric cord; 10 — damper-insulator (PVC tube, L50); 11 — cover (tin can); 12 — thread bandage (2 pcs.); 13 — main housing wall (AMts, sheet s1,5); 14 — screw M4 (2 pcs.); 15 — gasket (AMts, rivet from strips s1,5, 2 pcs.); 16 — removable housing wall (AMts, sheet s1,5); 17 — series-wound commutator electric motor (from “Veterok-3” vacuum cleaner); 18 — additional bracket (“mirror” made part 8); 19 — short guide (9 pcs.); 20 — screw M3 (2 pcs.); 21 — pressure disk (St3, sheet s3); 22 — screw M4 with split washer (2 sets); 23 — self-locking nut M4; 24 — screw M2,5 (2 pcs); 25 — dust protection (varnished cloth, 2 pcs.)
The transformer is taken from household radio equipment with a power consumption of 90 VA, though with a slight modification. The iron pack (Sh40x70 mm) and primary winding of three sections (155 + 28 + 155 = 338 turns of PEL-0.47 wire) are left as before, as is the frame, the rest is removed. A new secondary winding is wound — 340 turns of the same PEL-0.47.
The modified transformer is installed on the bottom of a box-shaped housing made of sheet textolite with ribs made of 15×15 mm aluminum angle.
Above the transformer on special stands, a mounting board with a rectifier and fuses rated for 0.5 A current is attached. The same fuses are also provided in the primary (mains) winding, but they are located in a special block (from household radio equipment) on one of the side walls of the power supply unit housing. And next to it on the other — an electrical outlet for connecting the mower’s electric motor.
The connecting wires on the mounting board are flexible copper, with a current-carrying core cross-section of at least 0.5 mm2 in soft insulation. Soldering is done with POS-40 solder.
The removable cover of the unit housing is fastened with M3 screws. Ventilation holes with a diameter of 10 mm are provided in the side walls. Well, a convenient handle serves for carrying.
The electric mower is reliable and comfortable in its maintenance. “Whims,” let alone malfunctions in the structure’s operation, have not been observed so far. And should they occur — the “electric mower” can be disassembled quite quickly and access to practically any of its units can be obtained.
Here, for example, is the algorithm of actions when replacing the electric motor in the mower drive. By unscrewing two mounting screws M4, the cover is removed. The removable housing wall is released. For this, screws connecting it to the base, as well as to the main wall, are unscrewed. The damper-insulator with the electric cord is removed from the socket-slot in the latter. And finally, by removing the knife from the head, the electric motor is extracted.
Main characteristics of the electric mower:
Dimensions (excluding handle and power supply unit), mm … 295x275x165
Rotational speed of working organ (knife), rpm … 13,000
Knife span, mm … 240
Electric motor power (from “Veterok-3” vacuum cleaner), W … 50
Mower mass with power supply unit, kg … 5
Power supply through transformer (220/220 V, 90 W) and diode rectifier (current up to 0.7A)
“Modelist-Konstruktor” No. 2’2002, I. BUYANOV
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