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High Performance Lawn Mower

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mower and workshop
The following log chronicles my ongoing project to decrease the time it takes to mow my lawn.

Why? Well, I enjoy engineering and analysis, and the lawn had to get mowed anyway. Second, I already had a 20 year old mower that was in rough shape. (ie: not a great loss if it blew up). Lastly, it is a simple and inexpensive machine.

NOTE: Scroll to the bottom if you want to see the oldest postings first. (most recent are at the top)


The Hartford Advocate Interview

The Hartford Advocate Interview
Ok... so alot of time passed before this past. The summer ended and I'll have to be happy with my 30 minute record.

Wonder of wonders, I got back from Burning Man...and the local artsy paper wanted to interview me about the project.




(Posted 12/13/2005 by john)

GPS based path tracking - 30 minutes

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click to expand
You know that turning point in a project when it goes from bad to worse? Well, um, I hooked a computer and GPS up to my mower and plotted the mowing path. The results are surprising.

First of all, I was really thinking about the path...and second, I had lots of expensive hardware on a bumpy ride (yes, I spilled gas on the computer). So it felt like I went very slowly and the lawn was done in 30 minutes!

The trick I think was to maximize long paths. Normally I would mow a section (for example "the back yard") and finish it before moving on to the next. Instead, I tried to avoid making turns and overlapped as necessary.

The actual driving time was less than 30 minutes. Perhaps the next improvement is to be made in the "pits".

NOTE: The GPS plot may not be 100% accurate. I have a theory that the software is trying to match previous paths. (It's the car navigation software Mapopolis on the PocketPC - The laptop in the picture was just for setup and configuration. I used Excel to do the plot.)


(Posted 8/16/2005 by john)

New Record - 38 Minutes

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Amazing - who would have figured moving the gas pedal from the left to the right would make such a difference. Actually, the new one is much more "car-like". Mowing the lawn got more precise...and it even has a nice idle now.

Check out the photos of the new pedal - it has a bolt to set the amount it can be pushed in, double return springs, and sits to the right of the brake/clutch.

PS: The plastic bag gas leak has been replaced with a shiny little bolt - The mower is even using less than half a tank for the lawn now. Wonderful!


(Posted 8/4/2005 by admin)

Mowing At Last - 45 Minutes

Yeah, I know - 45 minutes isn't very good. At least it's exciting to mow the lawn now. There's a long story there - let's just say I mowed it WITH the higher gear ratio but WITHOUT the new and improved gas pedal (coming next week). Cue the three stooges music...I basically took the exact same amount of time to mow the lawn but covered twice the ground. It was hair raising to shoot into the woods, and keep going back to pick up spots I missed. On the plus side, it did a nice job on the lawn. (hence, no more worries about the blades cutting poorly at speed.)

(Posted 8/4/2005 by admin)

Mower Deck Improvements (still no time result - It's been 10 days - lawn is starting to get long)

Mower Deck Improvements (still no time result - It's been 10 days - lawn is starting to get long)
With the mower deck off, I decided to fix and sharpen the blades (I hit a brick not too long ago). I also welded up a hole that has formed over years of use.

I always imagined the metal to be pretty thin (like sheetmetal on your car) because it used to have holes torn through it. Ummm, no - it's close to 2mm thick. In case you can't imagine that...heavy enough that I could hit it hard with a hammer and it wouldn't really dent.


(Posted 7/20/2005 by admin)

Improved Gear Ratio - $22 - (no mowing test yet)

click to expand
click to expand
OK...so this is fix that I've been waiting for. The drive pulley at the back of the mower is 11"...and I swapped it out for a smaller one of 6". This means that the top speed should be about 1.83x as fast.

But it's not that easy. First of all, I couldn't get the old pulley off. (and a replacement would've been $20 or more). SO, I just welded the smaller one to the side of the big one.

Second, I needed a smaller drive belt. This wasn't too hard to find...but getting the correct size was. It also involved designing a new belt path. There are several things you need to clear between the mower deck and the bottom of the "car". Regardless, after a few days of tickering and welding it's in and sort of tight.

For the test...Well, I haven't installed the mower deck yet - but it's all together AND it's really fast. (not fast enough to be scary - sort of like a slow go-cart.) I can hardly wait to mow the lawn.


(Posted 7/20/2005 by admin)

Improve the lawn...even quicker - 43 minutes.

Improve the lawn...even quicker - 43 minutes.
OK, maybe I am cheating on this one. I trimmed branches on the trees to make it easier to get around the lawn. This effectively made for more straight runs (less turning around things to edge). The results - It took roughly 43 minutes. (Actually, it took 38 for most of the lawn - plus a small section that was done a few days earlier for our tag sale.) On the other hand, the belt fell off at one point so the time also included repairs.

Second, the bumps are starting to make the engine stumble. Maybe it is just a gravity fed motor. Regardless, on a severe bump, the engine stumbles and a bunch of gas splatters out the top of the gas cap onto my legs. (partially solved with a little platic bag).


(Posted 7/10/2005 by admin)

Fixed Steering - 50 minutes

Fixed Steering - 50 minutes
This next stage didn't seem to be a huge mechanical change - but the lawn was much quicker. Basically, I tried to bend the frame straight (even with a 6 foot bar this was futile. I must have hit the tree pretty hard). However, I was able to carve away some metal to give the steering bar room to move.)

On the grass, I guess I developed some new techniques to use the pedal. Coming into a turn, I back right off which plants the front better and turning radius shortens. Coming out of the turn, I floor it and revs back up to full speed.

The results are staggering. The entire lawn took 50 minutes.


(Posted 7/10/2005 by admin)

Gas Pedal - Wow!!! - 90 Minutes

Gas Pedal - Wow!!!  - 90 Minutes
OK, the next stage was to free up the engine. The carb has an interesting "spring" controlled throttle. It sort of reminds me of the way vacuum would control the fuel needle in an old SU carb. Regardless, I added a pedal that would force it to rev higher. (haven't attached a tachometer to see just how much...but it is is significant).

The results are in - the lawn was done in 1.5 hours! That's less than half the time. The engine rattles quite a bit at maximum throttle with no blades spinner - but that's not a big deal. (makes it feel fun actually).

DANGER - Ok, so I messed up. Coming off a turn within the first 6 or 8 passes, I clipped a tree and bent the frame back at least 1 inch on the left. The rest of the lawn was painful to mow due to the rubbing steering components.


(Posted 7/10/2005 by admin)

First Changes - Lose the Cowling - 150-180 minutes

First Changes - Lose the Cowling - 150-180 minutes
OK...so what is the point of all of the metal up front? Maybe it keeps the engine clean (but the sides are open). Taking it off lightened the steering, and gave a much better view of the grass. It also seemed to tighten everything up (less unbolted metal to clank around on bumps).

Note: The other big change here was changing from a low blade height to the highest one. Amazingly - several weeks later and it seems to be making the lawn nicer too. Who knew?

Keep in mind - this was me trying to mow as fast as possible. Before, I used to hate the job and thus it would take an extra hour or so.


(Posted 7/10/2005 by admin)

Stock Machine - 210 to 240 minutes

Stock Machine - 210 to 240 minutes
We have a relatively large lawn - 3 acres and it would take roughly 3.5-4 hours to mow the whole thing. The mower would crawl at a painfully slow pace...slow enough that I would jump off to pull sticks out of the way.

Someday I'll find a photo of me on the mower when I was pretty young (under 10 years old - I am 30 now).

The base machine is a 808 Allis Chalmers with a Briggs and Statton 8hp engine.


(Posted 7/10/2005 by admin)