Ep. 43 | A homemade electric grass trimmer? A simple electric trimmer built at home from scrap, and it works really well

Electric grass trimmer from scrap: galvanized pipe + steel plate + belt-driven 775 motor, powered by a 3S5P 18650 pack through a boost module at 33V

One end of a two-metre galvanized pipe is cut at an angle and a steel plate is welded on tilted about 45° (like a small hoe); a handle is welded on wherever it feels right. Four holes in the plate take two bearings (as close to one straight line as possible), a shaft goes in and the excess is cut off, then an adapter, clamp plate and small pulley are fitted. A bracket for the 775 motor is welded on; once cool, the 775 motor and belt go on, and a powered test shows it runs smoothly. For power, 18650 cells make a 3S5P pack with a balancing BMS, fitted into a box with input / output / gauge / switch holes cut in it; the charge input gets a CV/CC buck-boost module with charge management set to about 12.8V; the battery positive runs through the switch into a boost module set to 33V feeding the 24V 775 motor — more torque and more speed. The box is fixed to the tail of the pole, the output lead connected, a shoulder strap tied on and trimmer line fitted (soft wire for now). A test cut at the front door works well — lighter and quieter than a petrol trimmer.

Outcome

Steps9 steps · click a frame to jump

1. 
   1. Pole: angle-cut the galvanized pipe, weld on the 45° plate and handle

   One end of the two-metre galvanized pipe is cut at an angle; a second piece makes the handle, sized to the grip; the steel plate is welded to the pipe end tilted about 45° like a small hoe; the handle goes wherever it feels comfortable to hold.

   00:00 – 00:40
2. 
   2. Drive: bearings, shaft, adapter, pulley

   Four holes in the plate for two bearings, as close to one straight line as possible; fit the shaft and cut off the excess at the mark; fit a matching adapter and clamp plate, a small pulley on the other end; a pulley on the 775 motor too; weld the motor bracket onto the pipe.

   00:40 – 01:08
3. 
   3. Fit the 775 motor and belt, test run

   Once the bracket has cooled, fit the motor and belt; power it up for a test run, smooth and fine; next, the power source.

   01:08 – 01:26
4. 
   4. 18650s into a 3S5P pack, fit a balancing BMS

   Build a 3S5P pack from 18650s, spot-weld it, fit a balancing BMS, and it’s a battery pack.

   01:26 – 02:56
5. 
   5. Cut the box holes: input, output, gauge, switch

   First cut the holes the box needs: input hole, output hole, gauge hole, switch hole.

   02:56 – 03:29
6. 
   6. Set the charge-management buck-boost module to 12.8V, wire the switch and gauge

   A CV/CC buck-boost module with charge management goes on the charge input, set to about 12.8V; the battery input connects to the module output; battery positive to the switch input; connect the gauge; switch output positive and battery negative go to the boost module; power on and it lights up.

   03:29 – 03:58
7. 
   7. Boost module set to 33V feeding the 24V motor

   Set the boost module to 33V, connect the + and − output leads; the 24V 775 motor gets stronger and faster; the idea: charge input → charge management → battery → switch → boost → 33V out; screws in, power section done.

   03:58 – 04:40
8. 
   8. Box on the pole tail, wiring, strap and trimmer line

   The box is fixed to the tail of the pole and the output power lead connected; a strap tied to the pole makes it easier to carry; trimmer line on the head (soft wire for now).

   04:40 – 05:26
9. 
   9. Cutting grass for real

   A test cut on the weeds at the front door works really well; lighter and quieter than a petrol trimmer.

   05:26 – 05:50

Bill of materials

Creator’s tips

• Fit the two bearings as close to one straight line as possible 00:42
• Run the 24V motor from a boost module at 33V for more torque and speed 03:58
• Weld the handle wherever it feels comfortable in your hand 00:16

Li-ion safety

• Let the bracket cool after welding before fitting the motor 01:10

Quotes