Hank's Electric Tractor Page

H. G. Dietz
http://aggregate.org/hankd/

Department of Electrical and Computer Engineering
Center for Visualization & Virtual Environments
University of Kentucky, Lexington, KY 40506-0046

Original April 28, 2020, Latest Update May 5, 2020


The opinions expressed in this document are those of Hank Dietz speaking for himself personally, not as a Professor at the University of Kentucky.


The Problem

I've always liked the idea of electric vehicles. My first real experience was in the mid 1970s, when my Dad and I modified my soap-box derby car, which was styled like a 1910 Mercer Raceabout, to be powered by the starter motor from a 1965 Ford Mustang. The belt drive didn't gear-down the motor speed enough, and I remember getting up to truly scary speeds driving it on the then-empty airfield at Mitchel Field. Later, my Dad's company built a not-for-road-use utility vehicle with a similar styling. It was available as gas, gas with electric start, and electric versions, and the electric one was displayed at IEEE Electro 77 as an example of an exceptionally efficient electric vehicle -- the trick was, it had a clutch and 5-speed transmission for its 1HP electric motor....

Anyway, twenty years ago, I moved to a house on a 10-acre lot in Lexington, KY. I never had more than 1/4 acre of yard before, and this 10-acre rough field quickly proved to be a challenge. We started by having a commercial mowing company "knock the grass down" to 6" every couple of weeks, but they were neither very good nor very cheap. So, I bought a 48" "Scotts by John Deere" riding mower to take the grass down to 4" or so... and soon after, I was actually mowing everything with that. It was challenging to say the least, although I have to admit that having the optional bagger did give me a way of collecting tons of grass mulch in minutes.

Clearly, I needed a bigger mower. After having a few come for trial runs, I decided on a 72" Scag Turf Tiger. It's a monster, but it did the job... so I eventually sold the 48" tractor. However, the Scag isn't great at towing things and maintenance service is slow (presumably lower priority than folks using Scags for commercial mowing businesses), so I bought another John Deere -- this time, a 54". That wasn't a bad combo, but as COVID-19 hit the USA, both my tractors needed servicing. I had been thinking about building or buying an electric tractor for twenty years, so I looked again to see if there was a viable electric replacement. Honestly, Mean Green makes what could be a great replacement of the Scag: the lithium-powered EVO-74" ZTR... but they're not really around here and the tractor isn't cheap. So, I looked more toward an electric that could replace the 54" rather than the 72". That's how I ended-up buying my 42" Ryobi, which is powered by four 100AH deep-cycle batteries. So, let's see if we can answer the question: are electric riding mowers really viable yet?

The Comparison

One big table can summarize a lot:

Property
Model John Deere LA175 Ryobi RY48ZTR100 Scag 72" Turf Tiger
Price (new) $2,800 $4,200 $12,000
Run Cost/Acre $2-3 $1-2 $3-5
Deck Width 54" 42" 72"
Travel Speed 5 MPH 7 MPH 12 MPH
Cut Speed (in use) 2 MPH 5 MPH 5 MPH
Max Deck Height 4" 4.5" 6"
Tall Grass & Weeds Cuts, but can Clog & Stall Mulching no, Discharge yes Cake
Twigs Unhappy Very unhappy You call that a tree?
Turn Behavior Large radius Zero radius Zero radius kills turf
Ride Tall, but stable Bumpy, can slide Like a tank
Noise Engine+deck == earplugs Deck only, can talk over Engine+deck > earplugs
Cuttings go where? On lawn, often clumps On lawn, as they should On you & everywhere
Towing stuff? You feel it No problem Works, but not intended
Safety? Interlocks, & stable Interlocks, but can slide Scary, but belt & rollbar

Conclusions

As I write this, all three tractors are fully working, and in the past week I have done hours of mowing with each. They're all ok. So here's the summary:

So, is the Ryobi electric a viable answer?

The answer is mostly yes. The "bursty" mowing style my Scag nudges me towards really isn't the best approach. Things look better doing the incremental cutting that the Ryobi inspires, and mowing is more pleasant in shorter doses with less noise and mess. Not having to deal with gas and belts is also a big win. I also have to give the Ryobi high marks as a farm utility vehicle, because it really works well for light towing.

The "no" part of the "mostly yes" answer has to do with the ability to convert a rough field into what looks like a trimmed lawn. The Ryobi is a lawn mower, and it doesn't deal as well with cutting non-lawn stuff -- weeds are ok (and the 4.5" max cut height helps), but it doesn't like twigs. If I run over a small branch with the Scag, there's nothing left but mulch. The John Deere mowing a twig makes some unhappy sounds, and twig pieces will survive the mowing, but there's really no harm done. The Ryobi doesn't do much to twigs, and in wet or really heavy mowing will need to have the discharge path cleared regularly. So, for acres like mine, the Ryobi alone isn't really sufficient; arguably, it plus a bush cutter would suffice, but using the Scag for rough cuts and Ryobi for frequent cuts seems to make the most sense.

Finally, it's worth saying a bit about safety. The Ryobi is certainly the inherently safest of the three to operate, but it really doesn't feel all that safe. The safety belt on the Scag feels like overkill, and I can't imagine what it would take to need the Scag's rollbar (other than power-flipping it by catching the rollbar on some overhead structure -- don't ask). However, the Ryobi bounces around a lot, and a safety belt would be a reasonable addition (the John Deere should have one too). The Ryobi's sliding potential also means I have to be very careful on slopes near my two ponds -- that, plus the fact the deck doesn't stick out the sides as much as on the other tractors, means I keep a little extra distance from most obstructions and can't cut under obstacles like fences. The John Deere's center of gravity is much higher, but the weight is evenly distributed between the engine up front and you in the back, while the Ryobi has the batteries under you with no weight up front -- it feels like you could pop a wheelie under the right circumstances. The Ryobi is also fast, and I can imagine it would be a little too responsive for someone not used to zero turns (e.g., it was for my wife); Ryobi does have a lower-speed mode for inexperienced operators.

So, electric mowers are pretty viable... as long as your property doesn't have lots of rough areas and slopes. Acres of grass, even tall grass with weeds, are not a problem.

One Last thing...

All three of my tractors have tires go flat regularly. Why? Ossage orange trees. Many of those twigs I was talking about have tire-killing spikes on them. I know there are now airless tractor tires, and I thought those should be the standard tires... until I looked at Tweel prices. They're running an order of magnitude higher price. That's insane. Let's hope that the industry soon realizes that airless tires should be the low-cost, high-volume, norm for slow-moving off-road vehicles.


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