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Discussion Starter #1
I started in mid September a new 4 x 4 excavator.



Quite simple but powerful enough: 4WD bobcat-style steering



Adjustable stabilizers at the front and leveling blade at the rear that can be used to level, lift the back and anchor the back when working with the backhoe.



Backhoe rotates 200 degrees with hydraulic cylinders and gear, 3500lbs pull force at the bucket



Lifan 2 cylinder engine 688cc 24 hp, hydraulic pump 12.5GPM



27 '' 6-ply tires (industrial machinery tires would have been too steep for the weight of the excavator, which is more important than the weight of a UTV vehicle)



All orders are adjustable in front of the seats (10 spools valves)



Valve to adjust the hydraulic flow without losing the pressure to have the right shoveling speed according to the work and the experience of the operator.



Speed ​​control valve for downhill.



Towing on the road without the need for a trailer.






 

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Looking good!! :thThumbsU
 

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I think the wheel base is long and the tires are too grippy for skid steer like a Bobcat. The early Bobcat's had really short wheelbase; shorter in length than width. Now they have increased the wheelbase for stability, but have 60HP engines to power turning. Since you are using the blade and out-riggers to stabilize while digging, the wheels are just for transport. I would consider moving the wheels much closer together.

Use counterbalance valves for downhill speed control; they are available to mount directly on motor depending on motor make/model.

Will you disconnect motors for towing?
 

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Discussion Starter #9
I think the wheel base is long and the tires are too grippy for skid steer like a Bobcat. The early Bobcat's had really short wheelbase; shorter in length than width. Now they have increased the wheelbase for stability, but have 60HP engines to power turning. Since you are using the blade and out-riggers to stabilize while digging, the wheels are just for transport. I would consider moving the wheels much closer together.

Use counterbalance valves for downhill speed control; they are available to mount directly on motor depending on motor make/model.

Will you disconnect motors for towing?
I am 55 '' wide and 53 '' wheelbase.

So I proportionally a little longer than the bobcat that would have 44 '' of wheelbase for this width.
This vehicle will not work on pavement, often gravel and dirt, it's easy. Especially since the weight on the rear wheels is lower than the weight on the front wheels, the rear wheels will be easy to derail.
The machine will circulate in the wood, so I wanted it not too late pouring when the terrain is uneven.
For engine power and traction, the Bobcat 60hp is more than 6000lbs without load in the bucket, and my excavator will weigh less than 2400lbs, and will have a lower movement speed, so much torque compared to the weight of the excavator.

I have not seen these motor with valves, are they expensive? My method of 'braking' is not perfect but very affordable.

The excavator tires would not ride well on the road, and the weight on the tow bar would be much too high. It's trailer tires that will be on the ground with trailer hubs, the 4 wheels of the excavator will be 6 '' to 10 '' in the air.
 

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Okay, you did your homework. I realized the weight was big factor, but I choose not to mention :hide: . About 5.8mph. I have a Melroe Bobcat that's 18HP; I have to set speed at about 3 mph to have enough HP for a 360.

What is pressure rating of hydraulic motors?
 

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Discussion Starter #13
Thank you!,

One of the biggest challenges is to manufacture it for less than $ 12,000 CND with hardware, new parts, consumables included and a small profit.

*

I used a valve that allows to adjust the flow that passes in the valve spools, as on my first excavator, it is very pleasant to be able to precisely adjust the speed of work according to what we do.

I'm going to have more tire torque than my first excavator.

The steering (bobcat) will greatly reduce the turning radius compared to my previous excavator.

On the other hand there will not be 2 moving speeds , limitations of costs.
 

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Discussion Starter #14
Nice work, you must have quite a shop for that kind of fabrication.
Thank you, but I just have a small garage of 14 'x 24', a small milling table top, a mini lathle, circular saw, grinders, a hydraulic press of my manufacture.

I have a new mig 275amp welder that saves me time with its big duty cycle.
 

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Discussion Starter #15

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Thank you!

I built it for someone who will take it this spring, I will try it before.


What is low pressure relief for?

The 7 spool valve stack already has a relief; no need for one on the PCFC. I can't tell for sure but it likely has Power Beyond as well (they sometimes have converter plugs); you should use that to power the 3 spool stack. If you use PB, there should a connection from the 7-spool to tank.

It wouldn't be to hard to add a second pump. I would belt drive the pumps on appropriate home made brackets; bell housings can be expensive. One pump about 8gpm and one about 16. Then you can select; 8,16,and 24. Then use a sprocket reduction from motor to wheel of 2:1. This would increase torque at low speed. Just saying :tango_face_grin:
 

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Discussion Starter #18
What is low pressure relief for?

The 7 spool valve stack already has a relief; no need for one on the PCFC. I can't tell for sure but it likely has Power Beyond as well (they sometimes have converter plugs); you should use that to power the 3 spool stack. If you use PB, there should a connection from the 7-spool to tank.

It wouldn't be to hard to add a second pump. I would belt drive the pumps on appropriate home made brackets; bell housings can be expensive. One pump about 8gpm and one about 16. Then you can select; 8,16,and 24. Then use a sprocket reduction from motor to wheel of 2:1. This would increase torque at low speed. Just saying :tango_face_grin:
The relief valve integrated in the flow control valve acts as global relief in case there is an overpressure in the 2 spools valves at the same time

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The relief valve at the bottom is to prevent the hydraulic motors from 'pumping' air down a hill. Adjusted at around 300-400PSI, the vehicle keeps a constant speed down a hill. In normal use, the ball valve is completely open, so that there is no unnecessary restriction on the return line.

A counterbalance valve would be more appropriate, should we put one on each motor?

*

If I had it built for me, I would have put more than one speed, either 2 pumps or 4 motors or hydrostatic pumps. But these components raise costs quickly and reliability is lower (a pump directly coupled to the shaft is reliable and simple) As I build a 4x4 excavator for the same price as a good towable Excavator without any traction with 1 cylinder engine ... (like an FCM, not a Chinese without an trumb and no hydraulic leg)
 

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The relief valve integrated in the flow control valve acts as global relief in case there is an overpressure in the 2 spools valves at the same time

*If the second group of 3 is fed by the power beyond port of the first group and the first group of 7 uses the tank connection, no overpressure is possible.

The relief valve at the bottom is to prevent the hydraulic motors from 'pumping' air down a hill. Adjusted at around 300-400PSI, the vehicle keeps a constant speed down a hill.

This relief then, is essentially a non-piloted counter-balance valve, as long as the weight or momentum of the vehicle doesn't cause more than the 300-400psi. The problem would be that it only works while the directional valve is shifted. You must have experience this problem before; when did it happen, probably when you were going down hill and tried to control speed by pulling back on the direction control, when you got near neutral, the machine went out of control. At that time, there is no flow to tank so this low pressure relief will not be affective.

The relief valve at the bottom is to prevent the hydraulic motors from 'pumping' air down a hill.
What you are describing is very close, but instead of pumping air, it is a lack of oil, or a void, called cavitation. There are a lot of ways to correct this. As you shift a cylinder valve, pressure is cut off to the cylinder slightly before cutting off the flow returning from the cylinder to the tank. This is to prevent pressure intensification. What you really need are motor spools in your valves. They cut off the pressure first, and don't cut off the return oil at all so that the motor with high inertia can coast to a stop. Coasting down a hill is not what you want. That's where dual counterbalance valves are used. You could use cylinder valves with cross line reliefs and anti-cav checks, which maybe slightly cheaper than C.B. valves. The simplest solution maybe to modify your control valves. Do they have metering notches? If so, grind the notches on pressure land deeper.

Probably the best way, is to have good brakes

In normal use, the ball valve is completely open, so that there is no unnecessary restriction on the return line.

A counterbalance valve would be more appropriate, should we put one on each motor? Each motor needs a dual counter-balance; backing down a hill is just as dangerous.

*

If I had it built for me, I would have put more than one speed, either 2 pumps or 4 motors or hydrostatic pumps. But these components raise costs quickly and reliability is lower (a pump directly coupled to the shaft is reliable and simple) As I build a 4x4 excavator for the same price as a good towable Excavator without any traction with 1 cylinder engine ... (like an FCM, not a Chinese without an trumb and no hydraulic leg)
Wished I lived closer.
 

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Discussion Starter #20 (Edited)
Wished I lived closer.
If one evaluates the force during a sudden stop

F = m x a

Maximum speed 6km / h = 1.6m / s

Fast closing time of a spool valve = 0.5 seconds (impossible to go from completely open to completely closed in milliseconds)

Acceleration = 1.6 / .5 = 3.2m / s2

F = 1090kg (2400lbs) x 3.2m / s2

F = 3488N = 784 pounds of force

This corresponds to a pressure shock of 1033PSI at the output of the motors. If we do the ration compared to the torque of engines at 2900PSI.

To this force would be added the force to generate by the degree of the slope.

I therefore conclude that at these low speeds a sudden deceleration can not generate sufficient pressure to explode an motor. A vehicle traveling at 40km / h could have overpressure problems when stopped abruptly on the pavement, in addition to projecting the driver from his seat (would then correspond to 1.1G)

I put cross relief valve on my first excavators because I was told that I had to put, but they were not used.

Thanks
 
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