Tractor backhoe - homemade

[Attono]

Finally I found some free time to continue building my backhoe..

Watching with great interest. Did you leave yourself enough room to get that pump out when it fails?

 

[BFreaky]

Watching with great interest. Did you leave yourself enough room to get that pump out when it fails?

Yes, it comes out easy. Front side is no problem, and the rear mount has screws with acess frm the bottom side of the frame. Hopefully it wont break down for a while...

 

[traktorz]

Thanks for answering my 4 questions in your post #116 here above. Your choice of mounting pin size, gives a hint on what buckets you plan to use. Seems also you're using the Brittish Standard Pipe thread. That's also stil the most common standard in Sweden.

Paying attention to the hydraulic pumps makes sense, and you seem to have a robust gearbox, which can handle the momentum forces from the PTO. How do you lock the gearbox from not spinning? I guess you need some flexible PTO coupling.

Be also sure to lock the tractors option of 1000 rpm PTO, if your tractor provides it. Or does your tractor provide enough force even at low rpm, so you can run the backhoe at PTO 1000?

An engineering design approach would be to model and optimize the hydraulic system in a CAD program or even in a spreadsheet, with model parameters assigned to valve block, pump, hoses and cylinders, etc.

I'll continue to read this impressive thread with interest.


P.S. Some ideas regarding my previous question #4:

Not having that luxuary, in order to trim the backhoes behaviour, some prototyping might be necessary to set up, I guess. Adding a few speed/flow control valves or even restrictors, as well as adjustable pressure controls valves on suitable points, would provide a quick tune up method, I think.

Some more ideas:
Adding PRV on each pump, although the valve block has a relief valve
Valve block with load checks
Priority flow regulator?
Surge relief valve?

Providing a third function option on the dipper stick
Cylinder holding valve for the stabilizer legs
Safety break-away couplings on hoses

 

[Renze]

Are these European standard names for different grades of steel?

If so what would be the equivalent in North America ( for anyone that can answer)

I guess Domex 700, Naxtra 70 etcetera are the equivalent of T1 ?? St.37.2 or S235 is mild steel. St.52.3 is a higher grade mild steel used for machinery.

 

[BFreaky]

The gearbox will have a small mounting plate at the front and a L profile at the back of the pump.
Tractos PTO has to be at 540 rpm and may not exceed 450 rpm because the gearbox has a speedup 1 : 3.8 .

Flow control valves will be mounted near joysticks in order to quickly adjust boom swing speed.
Third function option on the dipper stick is a must.

 

[ericher69]

I guess Domex 700, Naxtra 70 etcetera are the equivalent of T1 ?? St.37.2 or S235 is mild steel. St.52.3 is a higher grade mild steel used for machinery.

Renze;

Thanks for the comparison.

 

[Renze]

Tractos PTO has to be at 540 rpm and may not exceed 450 rpm because the gearbox has a speedup 1 : 3.8 .

i run my little backhoe from the tractor hydraulics, but as the oil pump is driven through the PTO shaft, i put the transmission in 4th, hi/lo in neutral and switch the oil pump to the transmission drive, to get full flow at 1200 engine rpm

Flow control valves will be mounted near joysticks in order to quickly adjust boom swing speed.

I drilled a wee little hole in an M10 bolt, then tapped M10 inside the elbows on the swing cylinder, screwed the drilled bolts into the elbows real right and then sawed them off

 

[Renze]

That's true, but I think 3 mm is not strong enough...reach of the backhoe from swing point to the tip of the bucket teeth will be 5.5 m, that's 18 feet...
It has to be stronger or it could bend. Main boom cylinder develops a force of 20.72 tonnes at 200 bar of pressure. I can't go under 6 & 10 mm plates...

By the way, out of interest i checked a Schaeff backhoe of the military, at work today. The cylinders are 125mm in diameter and with 210 bar they excert a force of 22 ton. The reach is also about 5.5 meter, and the vertical plates of the boom are 6mm and the horizontal are 8mm. Concidering the age and engineering standard of such a backhoe, i am sure it is just St.52.3 instead of Naxtra.

 

[BFreaky]

By the way, out of interest i checked a Schaeff backhoe of the military, at work today. The cylinders are 125mm in diameter and with 210 bar they excert a force of 22 ton. The reach is also about 5.5 meter, and the vertical plates of the boom are 6mm and the horizontal are 8mm. Concidering the age and engineering standard of such a backhoe, i am sure it is just St.52.3 instead of Naxtra.

Great, so material thickness will be ok...as I expected.
These days I've been finishing design details for the boom and dipper...by now all the drawnings are done except for the thumb, but I'm working on it...

 

[Renze]

What height will the section of the boom and stick be ? at this Schaeff it isnt more than 25cm high. In the picture it looks like your profiles are perhaps 40cm high, which means you can run with quite thinner steel walls of the profile...