Intro: Electric Lawn Mower
I have a small lawn in front of my house, which is a rarity in Indian houses. Ranaghat, where I live, is a suburban town in the state of West Bengal in Eastern India. I needed a lawn mower, and found that it would cost me around Rs.5000 (USD 120) to get one from the city. Hence I took recourse of some available machines and material at home and came up with a neat little design of an electric lawn-mower.The cost of the project was slightly less than Rs 1000 (USD 23), much less than what I would have had to spend to buy one.
Step 1: The Blade
The blade is a rectangular piece of iron. I got it cut out of an old hand saw (used by carpenters) that I had, and sharpened the edges at a workshop, and bored a hole in its centre. Through this will pass a bolt.
Step 2: The Iron Framework
Here is a disassembly of the iron framework. I got a blacksmith (in India, the best place to do it is at a place where they make window grills) to bend 6 iron rods to these shapes, And join the pieces together using nuts and bolts as shown. I did not have to work out the dimensions, but gave them a picture just like this one and they shaped the rods and aligned the holes. Do use washers at every joint, which I haven't shown in the diagram for brevity. The photos and videos will give you a rough idea about the size.
Step 3: The Drill-holder
This is the holder for the drill. It's drawn in a separate picture here. This too I made at the blacksmith's. They have enough junk lying around in their workshops to make one of these. The semicircular strips of iron were welded onto the heads of the two very long bolts. The reason I used such long bolts is that I needed the threading on their surface. These rod-like bolts will eventually have nuts screwed onto them from two ends, placing the drill-holder contraption in its place in the metal framework. The body of the electric drill will pass through the circular opening and will be clamped by nuts and bolts.
Step 4: Attaching the Drill-holder
Now, the interesting part. As you've seen before, this drill assembly is clamped horizontally, right in front of the framework. Take a carefull look at the assembly. The two vertical rods in front have channels running along their lengths.(This was made by using two square iron bars placed parallely and joined at the ends with small pieces of similar square iron bars of the same length as the speration between the parallel bars.) The ends of the drill-holder will pass through them and are tightened from each end by nuts.( Remember that the drill-holder's rods are bolts with threading on them). This could have been achieved by keeping holes in the vertical rods, as there are, at all the other joints of the framework. The purpose of the channel is to give us a facility to vary the height of the blade from the ground, by moving the drill-holder up and down before clamping it to a fixed position.
Step 5: Wheels
These are simple wooden disks with holes at their centre. These holes are big enough to hammer a ball-bearing through them. Ask the carpenter to make the holes slightly smaller than the outer diameter of the ball bearings. You'll need 3 such wooden disks, and hence 3 ball bearings.
Step 6: The Electric Drill
This is the lawn mower's engine. Buy any simple electric drill with a long cord that'll lead to a plug point. The drill should be a small one, that'll consume minimum power and will be light. Because cutting grass hardly requires any effort and the iron framework should be able to support the drill. My drill I bought for Rs. 700 (USD 16) and its power consumption is 250 Watts.
Step 7: Assembling
The machine is composed of the above parts.
In this short paragraph I'll explain how they fit together to make the lawn mower. So before assembling them you should have all this ready:
A thick bolt, a nut and washer to fit the bolt.
At least 9 sets of nuts-bolts-washers.
The 6 iron rods
The two halves of the holder for the drill
3 wooden wheels
An electric drill
Hammer the ball bearings into the holes on the wooden wheels.
Put together the assembly, joining the pieces by nuts, bolts and washers. This process puts the wheels in place too. Do use washers on both sides of the wheels so that the wooden surfaces of the disks do not rub against the iron rods which hold them in place. Only the washers and the heads of the bolts will make contact with the thick rim of the ball-bearings.
Once this is in place, screw into place the two halves of the drill-holder into the vertical channels. Don't tighten them right now. Place the drill, head down, in the circular space and clamp it tightly in place.
Pass the large bolt through the hole in the blade and tigthen it with a nut and washer. The remaining length of the screw will be held between the three teeth of the drill. So, in place of the drill needle you now have a T-shaped structure, that'll rotate like a propeller when the drill is switched on.
Step 8: Using the Lawn-mower
Now that the lawn mower is in place, take it to your lawn and adjust the height of the blade from the ground by moving the drill-holder along the channel. When done, tighten the nuts at the ends of the drill-holder. Connect the drill's wire to a plug-point nearby, switch it on.
One thing I haven't described is how to manoeuvre the mower. Well, the best bet is to attach a rope to the horizontal rod (just above and running parallel to the drill-holder), and pull it by the rope. I wouldn't recommend dragging it in circular paths too much,as this would generate twisting forces on the framework and especially the wheels and loosen the joints. But, of course, you can experiment and improve the design further and make it tougher.
See the attached videos :
1. Clamping the drill
2. Attaching the blade
3. Running the drill
4. On grass