Goldberg's the name...Rube Goldberg...

[PHPaul]

I've been wanting a way to trim ditches and under trees.

Sicklebar and disc mowers are just stupid expensive and it doesn't make any sense to spend four or five grand on something you'll use for 2 hours twice a year, if that.

They sell a commercial version of a 3 point hitch mounted string trimmer for compact tractors, but it's $1000 plus shipping and taxes, again more than I wanted to spend.

Being a serious packrat, I had most of what I needed to make my own. I had the gearbox, the trimmer head, the PTO shaft and most of the steel. Plus, it's a major hobby of mine, making my own equipment whenever practical.

I've got about $200 or $250 in it with pulleys, bearings, belts, shafts and what extra steel I had to buy.

I'm pleased with how well the Mark I works. I do have a couple of modifications in mind tho. I originally designed it to work on my Pasquali but between the articulation and slop in the hitch, it was nearly impossible to put the string head where you wanted it and keep it there. Works MUCH better on the Cabota. Not to mention power steering, air conditioning and cup holders...

The Pasquali has a 750 RPM PTO and I sized the pulleys to provide ~3000 RPM at the string head based on that.

The Cabota has a 540 of course. Add to that the fact that I'm running 18" of string (36" doubled over on both attachment points) and I'm running into a little issue with the string folding back in the heavy stuff. I've re-ordered pulleys to speed the string head up and I think that'll take care of it. I can always take smaller bites and just creep along in low range too.

I also need to fashion some sort of guard over at least the final drive belt. Big stuff like goldenrod tends to get under the belt and flip it off occasionally. Plus OSHA of course...

 

[Lil Foot]

Impressive!
Two questions:
What's a Pasquali?
What size is that string?
And you're right- don't let OHSA see that, they would fall over dead. On second thought, show it to them.

 

[PHPaul]

A Pasquali is an Eye-talian vineyard tractor. One lunger 20 HP diesel, full articulation, 3x3 transmission and true 4 wheel drive. In low/low and 4 wheel lock, it'll climb trees. In high/high it'll do 22 MPH down the road if you're brave enough.

String is .155 ribbed stuff that I had from the walk behind. Getting quite a lot better string life than I anticipated, even with it rubbing up against rocks and alders.

 

[85Hokie]

mmmm......
I teach my kinds Rube Goldberg stuff......they have to do something very simple in a complicated way....

YOU are a genius!!! Looking at the pulleys......guessing you are running at 540 pto speed, what is your final spindle running at? 2000+ rpm's?

 

[PHPaul]

mmmm......
Looking at the pulleys......guessing you are running at 540 pto speed, what is your final spindle running at? 2000+ rpm's?

Something like that. I need to turn it up a little, I have a bigger pulley for the gearbox on order, calculator says it should give me about 3500.

 

[85Hokie]

Something like that. I need to turn it up a little, I have a bigger pulley for the gearbox on order, calculator says it should give me about 3500.

What is the outer diameter of the spring? That has to make a hellva sound as it whips around! Bet it cuts really well too!

 

[PHPaul]

Rough guess, two 18" strings plus the width of the hub...42" or thereabouts.

And yeah, she do whistle a mite!

 

[Wbk]

That's pretty neat, how many hours did it take you? What did you use for the string head? There was a post on here a while back of two models and i noticed on the one that the line was twisted like a cable and very thick maybe 1/4". Thanks for posting the picture.

 

[PHPaul]

That's pretty neat, how many hours did it take you? What did you use for the string head? There was a post on here a while back of two models and i noticed on the one that the line was twisted like a cable and very thick maybe 1/4". Thanks for posting the picture.

Head scratchin', pencil sketchin' and parts gatherin' took 2-3 days.

I spent another day adapting a PTO shaft to the slip clutch on the gearbox. Had to manufacture a couple of parts which takes a while when all you have is a torch and a drill press.

About a half-day to make the mounting plates for the gearbox and string head and get them bolted together.

The actual welding and assembly took a day including clamping things up, looking it over, contemplating on it for a bit, measuring and eyeballing to make sure everything was going to line up, moving this, tweaking that and then tacking things together to see if it would actually work.

The string head came off a Crapsman walk-behind trimmer. The motor puked up a rod but I never throw anything way without stripping it for parts for "some day". Drives my wife nuts...

 

[Yooper]

Love that Rube Goldberg stuff!

 

[85Hokie]

Love that Rube Goldberg stuff!

Yooper,

here is a first year engineering class.....their job was to LIGHT the light bulb....they got a 9v battery and a little light bulb - had to have min 12 steps to complete.

This took about 15 hours or more to complete, about 10 class periods. Three people total, one leader,

this guy (he is a defensive/tight end on football team) got excited at the end, cause the first 45 times...... it did NOT work!!!!

https://www.youtube.com/watch?v=rZ0BcKjzO_0


this is one of my favorite 'bergs of all time :

https://www.youtube.com/watch?v=bl2U1p3fVRk

kids freak out as if they have to build something like it!!!!


'net said it took those HONDA engineers 600 times to get it right !!!!!

here is the breakdown of "Real engineering" ....

https://www.youtube.com/watch?v=Kh4zWeUDW-E

 

[Yooper]

That's awesome Hokie! Had to watch the Honda one twice!