Mower Math

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.

Playing in Traffic

I still keep up with a few technical journals.  I tend to read CACM’s “Kode Vicious” letters.  Often a bit on the technical side, but written from a realistic, if not cynical, perspective.

The latest one is on self-driving cars.  Short and uncomplicated, it lays out some of the high level issues for success in safety critical software applications.  Not as boring as it sounds, even for non-techies.

Kode Vicious Plays in Traffic

By George V. Neville-Neil

Communications of the ACM, Vol. 63 No. 6, Pages 25-26
10.1145/3396263

This Isn’t War

Briefly, the battle against COVID-19 was cast as a “war”.  I thought this was appropriate.  Over 100,000 fellow citizens have perished and the economy is in tatters. If COVID-19 were a country, there is no question we would be bombing the hell out of them, spare no expense.  And yet, we quickly backed away from this wartime footing which is usually the way we do things in the USA.  Everything worth doing has to be a war.  War on Poverty.  War on Drugs.  War on Terror.  War on Cancer. Why no War on COVID-19?

War allows the freeing up of resources.  Nobody complains about debt or the inconveniences.  War also means sacrifice.  Is this the problem?  Are our leaders unable to ask Americans to sacrifice, even when their own lives and the lives of their loved ones are at risk?  What am I missing here?

Fish Food Fail

We have a small pond out back. Used to have a nice koi until a raccoon got him.  Replaced Mr Koi with a few goldfish and some minnows.  By now we are down to one goldfish and a couple of minnows.  I feed them most every day, and noticed I was running low on food.  Usually I would go to the local pet store, since a small container lasts maybe a year, but with COVID-19 I decided to order it on-line.  Amazon had a minimum order of two. Ok, this is light stuff.  I ordered two.  Turns out I should have looked closer.  While the containers look identical, the ones I ordered are 3x – 4x the size of the one I have.  Now I have maybe a decades worth of goldfish food. Could be worse.  I know someone who thought they were ordering ten bananas on-line and was surprised to find ten *bunches* delivered.

The Japanese Approach to COVID-19

I followed COVID-19 in Japan somewhat closely.  I admit the reported lack of direction or serious restrictions seemed like a mistake to me.  But it looks like Japan had done a good job of really beating down the curve.  There isn’t a lot of agreement in the reasons, and there may be many, but it could be extensive contact tracing and following the “3 C’s” rules.

Experts are also credited with creating an easy-to-understand message of avoiding what are called the “Three C’s” — closed spaces, crowded spaces and close-contact settings — rather than keeping away from others entirely.

From Bloomberg:

Did Japan Just Beat the Virus Without Lockdowns or Mass Testing?

 

Plex Playlists Python

I’ve been using Plex for a while to manage my photos, videos and music.  Good stuff, I can recommend it.  Have had the server running on my old x86 PC for years.  Moving everything to my new Raspberry Pi 4 server was easy, except I couldn’t figure out how to make playlists.  Going through some old files it turns out that there was a bit of work involved that I had forgotten.  The server API supported playlists and they showed up nicely in the UI, except there wasn’t a place in the UI to load or create playlists.  Seems it has been this way for years.

There is a fairly simple command you can post to the server, but it requires a bit of specialized information.  I figured I could write a simple python script to take care of it.  Funny I wrote code almost every day for many decades but this is the first code I have written in almost a year.  It was actually a bit fun.  Decided to put it on gitHub in case anyone else wants to use it.