Ideas for Building an Electric Lawnmower

Swordman

100 mW
Joined
Jan 9, 2007
Messages
40
I'm thinking of building an electric lawnmower. Basically get an old lawnmower shell, mount a MY10XX motor on it and connect it to the blade and to power.

I know Lemmiwinks had a thread on the old VisfoV forum where he did exactly this. Hey Lemmiwinks, could you provide some pics and specs (motor used, batteries used, did you just use a switch for on/off, etc.) for that mower and let us know how well it worked (run time, how well it cut) for you.?
 
I'm very interested in this as well. Everything I have (chainsaw, weed eater, hedge trimmer, etc) are all electric. Wish the lawnmower is a push mower, so it's an easy job to cut my small lot of yard here in the 'hood.
 
Hi Swordman, gee that sounds like a great idea :wink:

Ok, I used a MY1020 Unite, whatever batteries I had lying around (3 x 7Ah and 3 x 12Ah strung in a series string of parallel pairs for 36V 19Ah) and a switch and 30A automotive relay. The hardest part is coupling the motor to your newly fabricated drive shaft for the blades. The method I used is crude but effective. I also considered using a standard 3/8" drive socket universal if this one didn't work. Dom posted links to industrial drive couplings that would also have worked but I don't have either the links or Dom's contact details.

I never bothered to note run time until last time I mowed the lawn. It was overgrown (as usual) and wet in patches to really work the mower over. I use a grasscatcher so had to stop and empty that at least 6 times, total time to mow was over an hour. Obviously the mower wasn't running 100% of that time, but near enough. It still had plenty of go, though I don't have any metering on it so I was only going on performance.

Photo #1: Fabricated top adapter plate, upper bearing housing and motor mounts

top_plate.jpg


Photo #2: Fabricated lower adaper plate, bearing housing (recycled though in hindsight it would have been quicker to machine one up from scratch), and new driveshaft. The driveshaft is an old motorcycle front axle I had lying around which happened to also fit some old bearings I had lying around. I shortened it and drilled and tapped the end to take a bolt

lower_plate2.jpg


Photo #3: Made a spacer and an adapter for the base plate to fit on. There's another spacer which you can't see that goes in between the upper and lower bearings. Otherwise when I tightened the base plate bolt it would try and crush the upper and lower bearings together and under load they would fail quickly

lower_spacer.jpg


Photo #4: I reused the original baseplate from the ICE because that made the most sense. I can use standard replacement blades and the cutting width is the same as original.

blades_mounted.jpg


Photo #5: Here you can see the top of the drive shaft. It has a shoulder on it so it doesn't fall through, and with the spacers it takes the load when the base plate bolt is tightened so that the bearings don't have any undue load on them.

The two pins are welded to a piece of bar which fits inside the end of the driveshaft and is secured with the split pin.

The plate with two holes in it is probably secured to the motor shaft with a grub screw since the motor has a convienient flat on the shaft. I don't recall for sure, but that's how I normally do it.

The end of the drive shaft has two flats on it so that I can attach a spanner to tighten the base plate bolt.

drive_pins.jpg


Photo #6: The motor is mounted and ready to run.

motor.jpg


Photo #7: Ready for a test run. It's charging using my 12V 1.6A smart charger. I switch from parallel for charging to series for power using 7 pin trailer plugs, at 1.6A it normally takes about 24hrs to recharge 57Ah (7Ah+12Ah = 19Ahx3 = 12V 57Ah) but since I have enough capacity in series (36V 19Ah) to mow the lawn it's not an issue. I just leave it on the charger until it's time to use it.

mostly_done.jpg


Photo #8: Dirty deeds, done dirt cheap. I spent another hour or two securing all the batteries properly and putting the finishing touches on the wiring but that's pretty much how the finished product looks.

lawn_mowed.jpg


I melted the first relay I used but I just replaced it with another 12V 30A one and haven't had any problems. There is one 30A fuse in the system which I haven't blown as yet. A couple of times the mower has nearly stalled on a hidden stick or rock but since it was towards the end of the mowing I assume the batteries can put out enough current to blow it.

The motor gets quite hot, last time after working hard in the hot sun it was hot enough that you could touch it but not leave your hand there, but as yet (maybe 1/2 a dozen uses, maybe more? I'm not keeping count) no problems.

Any questions, fire away!
 
Thanks lemmiwinks. Nice amount of detail. I'll have to study it for a while. The only question I have right now is your choice of motor. I seem to remember you had the MY1020 lying around and you used what you had. Do you think a smaller motor could would work ok, or do you think 500W is about right for the power?

I imagine you welded that nice mounting system together. I don't have access to any welding tools, but I could probably braze something together. As long as I don't hit any large rocks or tree limbs, that would probably work ok.
 
Actually I don't recall if I had the MY1020 lying around or not. I had this ridiculous idea where I was going to put two rotors from MY1016 200W motors onto a common shaft and wire them in series or parallel. It proved to be beyond my ability so I think I relented and bought the motor.

As to whether a smaller motor would do the trick, it might, I guess it would depend on how bad you let your lawn get. I find I have comparable if not slightly increased performance with the 1020 over the 125cc two stroke motor it replaced.

I did weld it up with my trusty $100-and-something arc welder. In Australia they're under $100 now (I've had mine a few years). It's not too hard to learn to weld, but if you're already set up to braze I imagine it would be plenty strong enough.
 
Ok,

Some more questions.

What do you think of a string-line based cutter (like a mounted weed eater) versus a traditional blade?

Even though it is more pricey, do you think NiCd or NiMH packs would do the job versus pushing all that lead around or would the amp draw be too much?

Although I can't imagine the amp draw is that much considering all you are doing is spinning something around which, most of the time, is under light load.
 
With my weed eater, the string lasts about 5 minutes. They make something that resembles a plastic chain that's supposed to last longer.

The real advantage of strings or other flexible cutters is they are more tolerant of rocks, sprinkler heads, etc.
 
Swordman said:
Ok,

Some more questions.

What do you think of a string-line based cutter (like a mounted weed eater) versus a traditional blade?

Funnilly enough I've been giving this some thought recently as I'd like a cordless electric whipper snipper (weed whacker, weed eater, whatever). However the conclusion I've come to is they need quite high rpm to work effectively. Think about it, if the string isn't going fast enough then it wont cut anything, it will just deflect. I don't think 2500rpm is fast enough, I could be wrong...(but I doubt it :wink: )

Swordman said:
Even though it is more pricey, do you think NiCd or NiMH packs would do the job versus pushing all that lead around or would the amp draw be too much?

I think that's a fine idea! I'm just a tightwad, plus I already had those batteries spare.

Swordman said:
Although I can't imagine the amp draw is that much considering all you are doing is spinning something around which, most of the time, is under light load.

Depends on your lawn, mine is under pretty decent load most of the time because it often gets overgrown before we get to mowing it, though I do take care to not slow the motor too much. But when my girlfriend mows she works the mower pretty hard. Mechanical empathy is not her strong point and I'm not sure she understands the concept of stalling an electric motor 8)
 
Swordman said:
Although I can't imagine the amp draw is that much considering all you are doing is spinning something around which, most of the time, is under light load.


I'll concur w lemmiwinks... my store-bought 12V mower is ok in low, sparse grass, but tall or dense grass can bog it down, especially later in the runtime.

Black and Decker has stopped making 12V and only makes 24V cordless mowers now.
 
I've seen electric weed eaters at my local hardware store, thought it was interesting. Anyone know of any company that sells electric law mowers that don't need to be plugged in?

[EDIT: Found a ton in google, nevermind :roll: ]
 
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