E-Tractor Build Log

[mylittlepony]

So I've been wanting to build an electric garden tractor for quite a while. I was looking at various ways of building my own chassis when I came across a rolling chassis on ebay. When I bought it I didn't have a clue what it was but I now know its a Simplicity 738 - they stopped making them in 1976 so god only knows how old it is

So I paid £66 for it and brought it home to see if there was anything I could use. It was covered in crap and looks really tatty but after a degrease and pressure wash it actually turns out that its in quite good condition. The rust is only superficial - the chassis is sound, steering works no problem, as do the brakes, and more importantly the transaxle seems to be fine. It has 3x forward gears and reverse, I worked out the approximate ratios:

1st 56:1
2nd 22:1
3rd 14:1
rev 14:1

I already removed the driven pulley but you can see the shaft close to the centre of the photo. That's some pretty good reductions! Now for a motor...... Considered brushless from various suppliers but settled on a Unite 36v 1000W MY1020. Yeah its brushed but it should be easy to control, easy to fit, torquey at low speed and more importantly cheap! I just hope 1000W is enough. The transaxle was originally driven by a V belt, I've settled on a BS 3/8" chain. I'll use a taperlock bush to fix the driven sprocket to the gearbox shaft. The motor will do 3000rpm so I've settled on a 12 tooth sprocket on the motor and 21 on the gearbox for around 2:1. That'll equate to tractor speeds of:

1st 1.58mph
2nd 4.03mph
3rd 6.33mph
rev 6.33mph

I figure I'll mostly use 2nd gear and reverse the motor rather than use the reverse gear. Sprokets and chain should arrive tomorrow. The motor is already here and I've welded up a motor mount to the frame. Once I get the sprockets I'll drill the holes to mount the motor.

Batteries..... Hmmmm....... My ebike runs on lipo but weight doesn't matter on a tractor, LiFe would be cool but the motor will pull nearly 30A and I don't want to splash out on a 30Ah LiFe pack. So I've settled on Deep Cycle SLA. Yeah I know, I know. I'll regret it etc. Well I've done the Peukert calcs and 36v x 86Ah (3kWhr) of Lead will give me a run time of around 2hrs at full power and alot more on less power. This is a garden tractor so I don't expect it to be running at full power all day - I expect it to spend most of its working day either stationary or running on much less than 1000W so I figure that's OK. The pack will weigh 60kg and cost me £260. All that lead will pretty much fill the space where the engine would have been. The lead arrives tomorrow so I'll start the mounts of it once it arrives.

Motor controller is on order, a 4QD Vortex 40-36. Lead time on that is around 10days apparently. It'll give me speed control, reverse and regen braking.

So far so good. Still alot of work to do but I'm really enjoying myself! I'd appreciate advice from anyone who's built something similar.

 

[amberwolf]

there's a guy by the name of jimdear over on diy electric car forums that has converted at least one full size tractor to electric, and there are at least a handful of other tractor conversions there, of various sizes and types, by him and other people, such as woodsmith. perhaps some of their experiences will help you out?

 

[wineboyrider]

Any progress?

 

[mylittlepony]

Yes I've made alot of progress. Apologies I gave up on the 'build log' as there didn't seem to be much interest on here. So here's a little update:

Work is sporadic since I have to travel for business so the project goes on hold for 3 week stretches which is a pain. Please note that the photos may not be cronological e.g. the next one showing the chain drive has the tractor in a much more advnanced state of paint.

I welded up a little motor mount and got the motor on there. Chain drive to the gearbox was really easy to install with the taperlock hub. Mounting the sprocket on the motor was a little harder since it engages with flats on the shaft but I dremelled the sprocket out to suit without a problem.

By then the batteries had arrived so I welded up battery trays out of 20mm steel angle, the same I'd used for the motor mount. This was the first welding I'd ever done and it was a lot of fun.

Then I removed the motor and spent a looooong time on paint. I used a cup brush to remove all the loose rust and paint then primed it with red oxide. Followed by a couple of coats of green gloss. All done with a brush but the finish is OK - I'd call it agricultural I say painting took a while but it was largely down to the cold temperatures we were experiencing, 4 days just to get to a touch dry state for a 2nd coat. The yellow paint you see was even worse than the green as it was so thin it took 4 or 5 coats! I ended up building a tent out of sheets and had a 2kW heater blowing for the duration just to get the paint to cure.

Once the paint had dried (eventually) I wired up the motor controller and threw the 3 new batteries- 3x 75Ah 12v deep cycle lead acid. They were the biggest I could fit. I put a simple foot switch over by the foot brake, a pot on the dash and a toggle switch for forwards/reverse. I had a short test drive in the snow and it worked really great. Accereration/deceleration was really smooth and almost silent. Power seems more than adequate. Very pleased

Then I stripped her down AGAIN ready to make up brackets for the seat and removed the front wheels so I could get new tyres and wheel bearings on the front. I've painted up the wheels front and back too.

This is an old tractor and some of the parts are very hard to find. I've been waiting 4 weeks now for the bearings and I've got another 2 weeks for the tyres to come from Germany. Once I get the front wheels back on I can remount the batteries and finish off the wiring.

I've got a +/- 30A ammeter for the dash and a 36v battery charge meter from a golf cart to fit too. Then all she'll need is a cowl over the batteries.

This is the latest photo I have. I'll take another and post later.

 

[mylittlepony]

Here it is with the seat mounted. As I said I just need the front tyres, front wheel bearings, to fabricate a cowling over the batteries and to mount my new gauges.

So far its been alot of fun. I can't wait to use it. I'll be needing to make or modify a bunch of different implements for it next.

 

[Hillhater]

Ha !
I like it..
about 20yrs ago, i bought a similar old ( 1968 ?) Roper garden tractor /mower with a blown engine. It was red,white and rust colored and very sad looking ( rotten tyres etc).
After a few months of work, she rolled out of the garage resplendent in "Deere Green" with Yellow wheels !! ...just like yours but still an IC motor..
The Kids and i had a lot of fun on that little "Deere lookalike" .
Wish i had some photos to share but ...
When i left the UK i passed her on to a friend in Shropshire where that 40" deck is still mowing .

 

[mylittlepony]

My 4 year old son's favourite colour is green so it had to be the 'deere' colour scheme. Besides I like the contrast of the green and yellow too

I was thinking of making some decals with the deere on them, just need to think of some sort of play on words to go on there - "Nothing runs like a e-deere" or something. Anybody got any ideas?

I've trawled the net for other e-tractor builds, there are quite a few. Here's one with a Simplicity 728 - mine's a 738 but there doesn't seems to be any difference. I haven't seen any that have taken my approach though. Everyone seems to go for a massive motor mounted in place of the engine, using all the same belts and pulleys as the IC version. The belts look so inefficient so I'm pleased with the chain drive I have.

 

[Jay64]

Nice work so far. I'm looking forward to the results.

 

[mylittlepony]

So its been a while since my last update - had to wait to buy a house with a bigger garden so I could test it properly! A couple of early trials before we moved house showed that I needed a bigger driven sprocket though as top speed was way too high so I replaced the 21T with a 30T. I finished off the dash with a fwd/rev switch, light switch, 30A ammeter, kill switch and decals. Then I fabricated a bonnet (hood) out of foam board (I made myself a hot wire bender with some nichrome wire) it was fun to do and quite easy. I also fitted 3x 12v 3W LED lamps in series in the front "grille" as much for asthetics as anything but they do work well, I'm sure I could mow in the dark if I wanted.

The lawn at the new house is around 2/3 acre I guess and had been neglected quite a bit so I bought a 38" lawn sweeper and a 30" ransomes sport cutter - both cheap on ebay.
As you can see the lawn was covered in cuttings and rather long. I've already made a couple of passes with the sweeper:

The tractor pulls the sweeper well, in that long grass it was pulling around 20A in 2nd gear. I don't expect the sweeper to work that hard again though as the grass was extremely long. After an hour of sweeping I reckon the motor was around 60degC, the motor controller was stone cold.

Next I mowed it with the sportcutter. I really wanted a much smaller set of gangmowers but they're really hard to come by for sensible money. Then this ransomes thing came up, I put on a silly low bid and won it for £50. These things are really heavy duty and designed for for full size tractors really, a set of 3 normally go for £2500 used. So I was a little worried that it would be too much for my 1000W little tractor. Anyway I made up a simple triangular hitch and went for it.

The mower is blunt and was binding since the seller had slopped paint on it to make it prettier for the ebay photos. Despite that the little tractor pulled it well and the mower chewed through the grass just fine. Some of the really long grass forced me to use 1st gear, the grass was quite wet too. After an hour I was pretty much done and starting to get the hang of manouvering the rig around the garden. The motor was really hot though having had 30A coarsing through it most of the time. So I put the tractor in the garage to cool and temporarily rigged a fan to blow air through the motor's vents.

An hour later and I was back out sweeping up the cuttings again.

So I'd call it a success. I'm rather pleased, it will be a useful little tractor. Batter capacity is ample, motor controller doesn't overheat, power is more than sufficient, basically it performs really well. I think the only modification that really needs to be done soon is to add a fan to air cool the motor and I should have a reliable little machine

Here's some pics:

 

[Kin]

Hey now, I know a lot of this forum seems only about speed and power, but that was a nice and wonderful conversion. Really in a sense beautiful to see how it transformed.

 

[TylerDurden]

I'm incredulous.

I have owned a few of those 7xx tractors and would never have thought a 1000W motor could do more than move it like a turtle, much less do actual work.

My current rig has a 10hp Briggs, but I use a dozer blade and rotary deck.

The Deere scheme is a hoot - the purists would cry blasphemy. :lol:

 

[bluegoatwoods]

That's really impressive......

Good job!

 

[mylittlepony]

Thanks for the kind words fellas

I'm incredulous.
I have owned a few of those 7xx tractors and would never have thought a 1000W motor could do more than move it like a turtle, much less do actual work.
My current rig has a 10hp Briggs, but I use a dozer blade and rotary deck.
The Deere scheme is a hoot - the purists would cry blasphemy. :lol:

Tyler - I know what you mean. I was rather surprised just how well the small motor copes. This thing was experimental, I'd half expected to need a 2nd motor to do any real work or to need powered attachments. I have a mains powered rotary mower rated at 1300W and it only has a 12" cut - it just doesn't seem possible I could run a whole tractor on only 1000W AND manage to cut grass. But it does! I guess it's partially down to the gearbox reduction to the drive wheels and the fact that a cylinder mower is that much more efficient than a rotary. I mean there is no way this thing would be able to swing a one of those rotary decks you usually see on ICE tractors. BTW I love the fact the colour scheme would upset 'purists'

For anyone who wants to follow in my footsteps here's some rough data. The ammeter bounces around alot due to the varying resistance of my bumpy lawn. Of course motor current also varies wildly depending on how hard the towed attachment is working, these figures should be worst case since the lawn was very unkempt and the mower needs sharpening. I'll try to improve on the accuracy of these figures later:

Not towing anything, motor at full speed, driving on grass
1st gear - 5A (180W)
2nd gear - 10A (360W)
3rd gear - 25A (900W)

Towing 36" lawn sweeper, motor at full speed, driving on grass
1st gear - N/A
2nd gear - 20A (720W)
3rd gear - N/A

Towing 30" Ransome cylinder mower, motor at full speed, driving on grass
1st gear - 25A (900W) (drops much lower when grass is dry AND shorter a lot of the time the mower was choking with grass and the wheels locking up and dragging)
2nd gear - 30A (1080W) (drops close to 15A when the grass is dry AND shorter the really long wet stuff was causing the mower to choke with grass forcing me to change into 1st gear)
3rd gear - N/A

Here's a link to the calculations I made for sprocket sizing. It gives the theoretical speed and thrust (draw bar pull) values too. I actually think the motor is running faster than 3000rpm since I'm sure the tractor is running faster than these theoretical figures. What I can say is that top speed in 2nd gear is just PERFECT for towing the mower or sweeper.

Next I think I need a some sort of linkage on the back so I can pull some sort of harrow or box blade for maintaining my long gravel driveway, there is definitely enough grunt for it. BTW does anyone know what the funny bracket on the back of the tractor is for? It looks like it might be for some kind of linkage but the holes are open at the top??

 

[TylerDurden]

Nice work.

The back bracket might be for a tiller attachment, (I never had one.) Could be a DIY version.

I love the fact the colour scheme would upset 'purists'

I don't know who would howl louder, the green-guys or the orange-guys.

 

[Jay64]

Fantastic build.

 

[ohzee]

Great work MLP - I had missed this thread until now and I find it very interesting that you were able to
do so much with so little. Sounds like you are pretty skilled as well. Id love to see some video of you riding
around. I am curious what the motor and the gear box sound like or if you can even hear them.

Bet it sounds neat cutting grass when all you can hear is the blades spinning.

Kickbutt work.

 

[mylittlepony]

@ohzee - I think 'skilled' is going a bit far I'll have to see about video. I'd hoped it would be quiet too but in actual fact it is surprising noisy to drive - however step back a couple of feet and the noise soon tails off. It is certainly nowhere near as loud as my neighbours' various conventional garden implements. Some weekends all you can hear is the wail of a 2 stroke.

All the noise comes from the transmission. I don't think there is anything wrong with it so guess it must have straight cut gears - its quite a high pitched whine. I changed the gearbox oil so I know it has oil in it. If I run the motor really slow it's silent but the tractor is only creeping along. The motor and chain drive are silent, I know this as I've run the motor full speed with the gearbox in neutral. I suppose a noisy transaxle isn't normally noticable on a gasser.

Despite the noise what is really good about electric is the silence and zero energy consumption when you stop. When you get off an ICE tractor you always have the dilemma of 'How long am I stopping for? Is it worth stopping the engine?'. With electric you just climb off, I usually remove the key for the safety of the kids but its not as though I need to start the engine when I come back.

I'll be back home soon so I'm planning some further mods:

1) I've bought 2x 18v Bosch strimmers really cheap. I want to mount them somewhere and run them off the tractor's battery.
2) I've also got plans to make a small 3 point hitch as I want to be able to rake the driveway and lawn. I'll make the implements too.

Not sure which I'll do first but watch this space.....

 

[fechter]

Very nice! I used to have a 1970 International Harvester Cub Cadet that I wanted to convert, but never got around to it before letting it go. I'm surprised the motor handles the load so well. If it runs hot, adding forced-air cooling would help. You could also possibly add a second motor for twice the power.

 

[Xanda2260]

This thing looks awesome! You've made me want to build one!

Very nice work!

 

[mylittlepony]

I've been busy with the tractor, making further mods and doing a lot of work with it. This has become a proper little workhorse - not just an EV project but a working tool. Here's a video of me mowing.

http://youtu.be/vgQniLh9fEc

As for the other mods - well they're more 'tractor' mods than 'EV' mods so take a look over here for more.

 

[The fingers]

Love the color scheme, an electric "deer" (sic) to compliment the "electric horse". It would make the news worth watching or the paper worth reading! (you can take the boy out of Iowa but you can't take the Iowa out of the boy) My compliments for an amazing piece of machinery and a fine looking lawn!

 

[hillzofvalp]

I used that motor In a pocket bike at 3.2kW with bad results. It is definitely going to burn up after the 1000W continuous rating... I imagine though on your machine you level off around 1kW. Not sure about spinning a full deck of blades.
Edit: missed the second page. Good JoB! Solved the problem of powering a deck!

 

[Timma2500]

Thats fantastic!

It looks great and seems to punch above it's weight work wise, well done!


Paul

 

[grindz145]

Nice! I know you guys don't get much snow in the UK, but a it would make an excellent driveway plow machine too!

 

[hillzofvalp]

how cool would it be to buy a used robot mower and give it new life with some old life or lipo...