Mini dozer build!

[m_c]

When you get that little oil flow it will be a problem. Track a mini digger slowly and chuck a brick Infront of it. They will come to a stop.

At very low flow you lose pressure due to leakage, which is what causes the loss of torque, however on a mini digger, it's more to do with how they regulate the speed. They just rely on a basic spool valve, so don't have any proper flow/pressure control. If you were to use proper flow control that limits flow but still allows full pressure, they wouldn't stall anywhere near as easy.

The issue is variable flow control isn't a simple thing to implement, so on a mini digger where the most common speeds are stopped, or flat out, a couple relatively crude spool valves is acceptable.
However on something like a mini dozer where the main use is drive at varying speeds, using a couple spool valves to regulate oil will quite quickly heat the oil, so you really want a more efficient and controllable setup.

 

[Pete.]

When you get that little oil flow it will be a problem. Track a mini digger slowly and chuck a brick Infront of it. They will come to a stop.

Same with a car, motorbike, gondola etc...

 

[Agrismith]

At very low flow you lose pressure due to leakage, which is what causes the loss of torque, however on a mini digger, it's more to do with how they regulate the speed. They just rely on a basic spool valve, so don't have any proper flow/pressure control. If you were to use proper flow control that limits flow but still allows full pressure, they wouldn't stall anywhere near as easy.

The issue is variable flow control isn't a simple thing to implement, so on a mini digger where the most common speeds are stopped, or flat out, a couple relatively crude spool valves is acceptable.
However on something like a mini dozer where the main use is drive at varying speeds, using a couple spool valves to regulate oil will quite quickly heat the oil, so you really want a more efficient and controllable setup.

But this project doesn't sound like it's going to the great expense

Same with a car, motorbike, gondola etc...

Exactly it's why we have gearboxes

 

[Pete.]

I saw a calf dozer at the Much Marcle show a few years ago, there's not much to them

View attachment 381911

Video of this working at 3mins 21sec

 

[Erie Fred]

In the US they get a lot of snow, and a Quad with a snowplough blade on the front seems to be the weapon of choice for rural dwellers. Used 4WD quads are not that expensive, (even at the moment, when you can't buy new ones,) and a lot easier to set up than making a tracked vehicle from scratch.

Uhm....yeah.
The snowplow was a cheap option when buying a quad a few years ago so you could get "Wife's approval" for your toy.
I see these "people" out there flying down their driveway trying to convert speed into push all the time. Most around here use a pickup truck (f-250 or bigger) with a Meyers or similar plow.
Of course I don't......

This case 1470 with custom made 10' wide X 48" high blade is what I used to use.

And I clean up the corners left by the Ford with the Bobcat with a 6' blade:

 

[Pete.]

Uhm....yeah.
The snowplow was a cheap option when buying a quad a few years ago so you could "Wife's approval" for your toy.
I see these "people" out there flying down their driveway trying to convert speed into push all the time. Most around here us a pickup truck (f-240 or bigger) with a Meyers or similar plow.
Of course I don't......View attachment 383000
This case 1470 with custom made 10' wide X 48" high blade is what I used to use.
View attachment 383001

And I clean up the corners left by the Ford with the Bobcat with a 6' blade:
View attachment 383003

Does that bobcat have the single-lever operation? FWD-REV by push pull and left-right by twisting the t-handle on top? I drove one like that years ago and hated the damn thing.

 

[Erie Fred]

Does that bobcat have the single-lever operation? FWD-REV by push pull and left-right by twisting the t-handle on top? I drove one like that years ago and hated the damn thing.

Nope, it has the standard 2 handles (one on each side) and the foot pedals for the bucket.
I think the T bar ones where the Early Gehl's.

 

[Pete.]

Nope, it has the standard 2 handles (one on each side) and the foot pedals for the bucket.

Ah, the 'sensible and intuitive' option. I don't know what they were thinkng with that earlier one I operated but it was horrid. The best ever Skid steer I operated was a 2 tonne Belle. Smooth as silk to drive and very nicely set out contrls. I expect that the newest generation are very good too.

 

[Erie Fred]

Ah, the 'sensible and intuitive' option. I don't know what they were thinkng with that earlier one I operated but it was horrid. The best ever Skid steer I operated was a 2 tonne Belle. Smooth as silk to drive and very nicely set out contrls. I expect that the newest generation are very good too.

I've never heard of those, could you post a pix or linky please ?

 

[Pete.]

I've never heard of those, could you post a pix or linky please ?

Don't have any pics of it, long gone now and I can't remember the model. My company bought it new maybe 20yrs ago or more and it did thousand of hours demo work. Pretty basic to look at by modern standards but very nice to operate nonetheless.

 

[Bornfree]

Ah, the 'sensible and intuitive' option. I don't know what they were thinkng with that earlier one I operated but it was horrid. The best ever Skid steer I operated was a 2 tonne Belle. Smooth as silk to drive and very nicely set out contrls. I expect that the newest generation are very good too.

Have you ever driven a Thomas skid steer they do one with a 6 cylinder engine. Amazing machine.

 

[Pete.]

Have you ever driven a Thomas skid steer they do one with a 6 cylinder engine. Amazing machine.

Nope - never even heard of them. I'll keep an eye out now though.

 

[Stingray]

At very low flow you lose pressure due to leakage, which is what causes the loss of torque, however on a mini digger, it's more to do with how they regulate the speed. They just rely on a basic spool valve, so don't have any proper flow/pressure control. If you were to use proper flow control that limits flow but still allows full pressure, they wouldn't stall anywhere near as easy.

The issue is variable flow control isn't a simple thing to implement, so on a mini digger where the most common speeds are stopped, or flat out, a couple relatively crude spool valves is acceptable.
However on something like a mini dozer where the main use is drive at varying speeds, using a couple spool valves to regulate oil will quite quickly heat the oil, so you really want a more efficient and controllable setup.

It is going to be more of a toy, as for forward/reverse speeds it slow to normal walking speed would be ok, I am going to speak to the likes of flowfit to ask if they have high torque slow speed hydraulic motors, if I can get this information then I can look at a final drive solution, my biggest problem just now is finding a solution that works with no issues, I would hate to build something that did not work or hydraulic motors went bang…

 

[Stingray]

Have you ever driven a Thomas skid steer they do one with a 6 cylinder engine. Amazing machine.

I’ll Google that!

 

[Erie Fred]

It is going to be more of a toy, as for forward/reverse speeds it slow to normal walking speed would be ok, I am going to speak to the likes of flowfit to ask if they have high torque slow speed hydraulic motors, if I can get this information then I can look at a final drive solution, my biggest problem just now is finding a solution that works with no issues, I would hate to build something that did not work or hydraulic motors went bang…

How about the drives from a zero turn mower ?
You would add a chain sprocket to the axle/output shaft, for slower speed & torque multiplication.

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[m_c]

It is going to be more of a toy, as for forward/reverse speeds it slow to normal walking speed would be ok, I am going to speak to the likes of flowfit to ask if they have high torque slow speed hydraulic motors, if I can get this information then I can look at a final drive solution, my biggest problem just now is finding a solution that works with no issues, I would hate to build something that did not work or hydraulic motors went bang…

You could probably get away with a basic two speed setup then.

For motors, you'll need to do some calculations.
Something like a 16cc displacement basic gear pump/motor https://www.flowfitonline.com/categ...roup-2-gear-motor-reversible-16cc-elbow-ports would give ~50Nm at 180bar (this was the first online calc I found - https://www.hk-hydraulik.com/en/hydraulics-calculator ), but at low speed efficiency will be pretty horrendous.

Whereas something like a 98.6cc FPPM motor https://www.flowfitonline.com/produ...l-keyed-shaft-2-hole-mount-high-pressure-seal would give over 400Nm, and be better suited to low speed.

But then you need to balance that off against how much pressure/flow you're going to have.

I'd probably start by thinking about how much pushing/pulling force you'd like to have.
Then you need to work through the system to see what is feasible.
If know how much force you'd like, next figure out what the diameter of your track/drive sprockets are going to be.
You can then work out how much torque you'll need at the drive. You can then run some figures to see what displacement motors would work, and at what pressure.
Once you have the required pressure/displacement, you then need to think about speed/flow, which is where you need to work out what is possible from your chosen power source.

Once you have an idea of all that, you can think about control, which will likely cost you more than the motors and pump.

 

[Erie Fred]

You could rig up qty (2) small engines, one for each side.
Much like a Terex dozer.

 

[knighty]

have you picked the engine yet? you said 20hp but no sure if you picked exact engine yet

pick your engine, check the power curve and guess how many rpm you want to run it at - 80% load is normally the efficiency/reliability sweet spot

pick a hydraulic pump suited to that power/rpm (remember how you're going to drive it or rpm?)

then pick two hydraulic motors that match that flor rate for the rpm you want?

 

[Rannsachair]

Reducing flow reduces speed.
Reducing pressure reduces torque.

The hardest part with hydraulic motors is controlling speed.
Simple single/two speed is reasonably simple.
Variably speed is more complicated, as you need decent flow control to avoid cooking the oil.
I'm sure if you asked @Rannsachair nicely, he might give his input on the more cost effective methods to achieve variable speed and still be able to steer.

A few ways to do this.

I used to work for Bosch Rexroth designing radial piston motors, skid steers were our biggest market. Problem is that high torque low speed motors are expensive, may be best just looking for a suitable donor vehicle rather than buying individual components.

Ideally you want a tandem variable displacement/swash plate type pump for the drive motors and a tandem gear pump for the auxiliary hydraulics, again expensive to buy new.

 

[dan.taylor.1]

Nope - never even heard of them. I'll keep an eye out now though.

Our skid steer is a Thomas, T 105. They're Canadian, not sure they make the bigger models now, just small tracked one's.

Just 2 lever on ours, forwards and backwards controlling wheel speed and direction for each side, right lever left/right controls tip, left lever left/right controls boom (think I've got them right way round?!) and 3rd service is a diverter valve via a button on the right lever and uses the tip hydraulics.