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?
Tractor backhoe - homemade
- Thread starter BFreaky
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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
Bronze Member
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
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
Super Member
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.
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.
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
Veteran Member
Renze
Super Member
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
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
Super Member
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
Super Member
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...
Renze
Super Member
With that profile height i would go with 4mm side plates and 6mm horizontal, or you spend a lot of money for nothing, while reducing the capacity of the digger due to its weight.
To me this sounds like the boom of a full size 13 ton Atlas excavator
How wide is the profile ? With breadth and height, i can give you a calculation of the bend force in ton/meter it can take at various plate thicknesses, so you have a broad indication of where you're at.
Renze
Super Member
Will get back to you tonight, i'm at work now and lunch time is over in a minute
Renze
Super Member
OK its weekend, got time for some calculations: As a reference i take the aforementioned Schaeff backhoe, which has 125mm cylinders for boom and stick. The profile is 240x260mm, the horizontal flange is 8mm and the vertical flange is 6mm. It would have a bend resistance at yield strength of 18 ton/meter. Now we must keep in mind that both cylinders in this design (just like in your design) are both mounted on top of the boom, so they pull on the same bracket: that reduces the bending moment at the section right inbetween them. It has the boom and boom cylinder attachments spaced 40cm apart, so at 210 bar it would make 10.28 ton/meter force. the ratio between that would be a factor of 1.75 This is not an actual safety factor, as it is just indicational, because other stresses are left out of the equasion. However it gives an indication
If you want the same moment of inertia of the profile with the 200x430mm outer dimensions, 4mm would have the same moment of inertia as the schaeff backhoe with a much lower section height, but thicker plates. however because the profile is much higher and the cylinders arent spaced further from the neutral line of the profile in the same ratio, i would take 5 or 6mm for the vertical flanges and 4mm for the side plates so you have a big safety margin, and some meat to weld your cylinder attachment brackets and boom pivots to.
I havent set up the forces all up in a calculation program with consoles, and tensile forces which the cylinders apply on the profile (other than just bending) but you're wasting money when going with 8mm material, with the section height of the profile you drew
If you want the same moment of inertia of the profile with the 200x430mm outer dimensions, 4mm would have the same moment of inertia as the schaeff backhoe with a much lower section height, but thicker plates. however because the profile is much higher and the cylinders arent spaced further from the neutral line of the profile in the same ratio, i would take 5 or 6mm for the vertical flanges and 4mm for the side plates so you have a big safety margin, and some meat to weld your cylinder attachment brackets and boom pivots to.
I havent set up the forces all up in a calculation program with consoles, and tensile forces which the cylinders apply on the profile (other than just bending) but you're wasting money when going with 8mm material, with the section height of the profile you drew
I've taken everything you said into consideration and decided to go with thinner side plates so I will use 6 mm
ST 52.3. Also, I will lower the boom profile a bit to loose its weight.
Renze, thank You for your time, effort and help, I appreciate it.
ST 52.3. Also, I will lower the boom profile a bit to loose its weight.
Renze, thank You for your time, effort and help, I appreciate it.
Renze
Super Member
Sorry i meant to say, i'd take 5 or 6mm for the HORIZONTAL (narrow) flanges and 4mm for the side plates.
The thinner plates are also much easier to clamp into position, you simply cant roll them that precise so you'd allways have to clamp them to fit.
The thinner plates are also much easier to clamp into position, you simply cant roll them that precise so you'd allways have to clamp them to fit.
Sorry i meant to say, i'd take 5 or 6mm for the HORIZONTAL (narrow) flanges and 4mm for the side plates.
The thinner plates are also much easier to clamp into position, you simply cant roll them that precise so you'd allways have to clamp them to fit.
Well, I kinda like to make things a little stronger then they have to be, so I'll put 6 mm. :-D
Renze
Super Member
Most determining factor in the durability of the backhoe is how you lead the forces into the profile: Most excavator booms are pretty thin walled, and therefor have large overlapping brackets to which cylinders attach, do divide the force over a wide area of the wall of the boom tube. Determining the profile size is the easy part, but determining the details on how to lead in forces and where to gusset etcetera, is what makes the quality of a product... However judging from the photos of the swingframe you already finised, you've got a natural talent on that
Let's say I can "see" the whole thing in my head and can anticipate how it will behave...that's why i draw so much before doing anything. I also intend to distribute the forces on the side plates by adding large sufrace plates with circular holes to make them as light as possible. This is now the final design and it's already ready for cutting. It will look like this:
