There is a pulley on my mower below the battery below the seat that drives the differential / transaxle.  It would be nice to keep this part but nicer to drive it directly from an electric motor rather than via the complicated arrangement of belts and pulleys that go all the way to the 14 HP gas engine in the front.

This differential is just forward / neutral / reverse and had no gear shifting; that is all done by the belts in an unusual arrangement using “variable pulleys”. The biggest problem was finding out the gearing ratio of the transaxle.  Was going to put it up on blocks, (somehow) get it running and (somehow) count the revolutions of the wheels and the main pulley.  Maybe use a video camera.  This all seemed complicated and even dangerous, so I had another look at doing this without the motor running, and without dismantling the whole rear end.

Turns out I could prop one of the pulleys that maintained tension on the belt with a piece of pipe I cut, then putting the mower in drive and then turning the pulley it would inch forward.  Pieces of tape on the pulley and the tire let me keep track of the number of revolutions.  Turns out spinning the input pulley to the transaxle 21 times turns the 17.5 inch tires once.  This comes out to a little  over two inches (2.618) of forward progress of the mower for each spin of the transaxle input.

The big question is: what sort of motor would I need to drive this directly?  Electric motors tend to be 3,000 to 5,000 R.P.M.s.  Would that be too fast, or too slow?

For 3,600 R.P.M. (for instance) times 60 gives 216,000 R.P.H (revolutions per hour). At 2.618 inches per revolution, we would go over half a million inches in that hour (565,488 to be more precise).  There are 5,280 x 12 inches in a mile. which gives 8.925 M.P.H.   which is pretty reasonable.   So I can directly hook an electric motor directly to this transaxle and get a reasonable speed.  I like this idea because it eliminates all the belts and pulleys, but keeping the transaxle keeps things like the brakes and the back wheel arrangement the same.

While researching this I learned that people race riding mowers.  Might be a new hobby in my future.

I have a 20+ year old MTD Yard Machines riding mower.  I’m not much of a mechanic but over the years I have managed to keep it running.  No real engine work, but just about everything else has needed attention at one time or another.

I’ve been thinking about doing an electric conversion on this one but felt like it was a bit too much out of my skill set.  Saw some plans on line but many of them seem already dated.  With all the eBikes, electric motorcycles, scooters, etc around these days, the technology has really matured and lots of components are available that would make this much easier than it would have been even a year or two ago.

You can even buy new electric riding mowers at Home Depot now, but they tend to be pricey ($2500+), and that may be the right way to go, but where is the fun in that?  Can’t say I’ve decided to convert the old mower, but might start putting some notes out here as I go along.

Most of the early decisions would be around the engine.  It is a 14 HP.  Should I just replace it with a suitable electric motor?  This seems to be the simplest way at first.

Another approach is to use one motor to drive the wheels, perhaps directly from the rear, and two smaller motors to drive the blades.  This eliminates all the pulleys, belts and transmission functionality and could make for a clean simple design.  I’m leaning toward the three motor solution, but need to look at the rear transmission.

BTW, this lawn tractor / riding mower seems to be a popular if not durable beast.  Lots of YouTube repair videos out there which can give you some ideas and a good look at the internals without having to take the machine apart.

Spent last night looking at some smaller motors for the blades and associated controllers.  Interesting stuff.  This motor kit for an electric scooter also caught my eye.

A long time ago I read that your lawnmower could produce more pollution than your car.  At first this didn’t sound right, because lawnmower engines are so small.  But they are unregulated and don’t have all the sophisticated pollution control equipment of autos.  The article Cleaner Air : Gas Mower Pollution Facts says a mower produces 11x the pollution of a car.  I believe it.  The good news is I see lots of new electric and battery powered mowers at the stores.  Things like this can make a big difference.  So before you rush out and buy that Tesla, get a new mower!   Electrics are quieter, too.  Next big change should be heavy equipment used at construction sites.