diy crawler,hydraulic question.

[patp744]

Ok.in my frustrating search for a small metal track crawler loader , like the old struck magnatrac.i started to look at the cub cadet diy dozer conversion.
This conversion is within my building and welding skills , and projects like this are enjoying to me..
The only thing I don't like about using the tractor rear end is it won't function like a real crawler .to turn you apply brake to one track so that it skids for a turn..
If I build one , I want it to work like a real crawler with the ability to put one track in forward and the other track in reverse at the same time ..
My hydraulic question. .
If I pick up two drive motors from a bobcat style track loader how do I size the hydraulic pump.
Actually I was thinking of two pumps .
One for drive, one for loader operation .

Now my termite t5c minibackhoe has two pumps stacked back to back . Direct off the motor . This setup would be ideal.
But since I didn't buy anything, or make anything yet, belt driven is a possibility too.

I was even considering buying an old cheep bobcat for all the parts until I saw the series of chains and clutches they use to make the travel system work.
Not enough room for that set up.

Or maybe an old Toro dingo ,but there prices are to high for a hobby project .
Unless I find one with a blown motor ,witch would be just fine with me.

My thinking is two drive motors , one for each track ,direct to the drive track.

Any thoughts ? ?
Websites to look at ? ?

Thanks

 

[J_J]

You size the pump by the motor volume in GPM's and pressure rating.

You can drive some hyd pump directly or chain driven to the wheels or track.

You can split one pump flow using a splitter, or use two pumps.

Loader pump could be a fan belt driven pump. .

 

[Bladehauler]

why not use a zero turn drive system ? surplus center had some for sale a while back . just my .02

 

[aczlan]

why not use a zero turn drive system ? surplus center had some for sale a while back . just my .02

Bad idea unless you REALLY gear it down. Zero turn drive motors are not really meant for pushing or pulling like you need for a dozer.

Aaron Z

 

[patp744]

I thought about the zero turn myself but then took at the work load there set up for.
I figured they are to light duty for my needs .

Thanks for the help.

 

[patp744]

Ok..so I just went over to surplus center.
It looks like I'm going to spend a lot of time there..
Although I have very little idea what some of the direct wheel motor numbers mean ,I guess I should look up a bobcat track drive motor to see what they are rated for so I have some kind of baseline .

 

[J_J]

First determine the HP you have available so you can choose a pump that can maintain the flow and pressure.

 

[patp744]

Alright .. a safe bet would be in the 27 to 34 hp range. . Shooting for diesel but may end up gas ..

Dose anybody know what the "cu in. " is referring to when looking at direct wheel motors ? I assume it's cubic inches. .
But cubic inches of what ? ?

 

[J_J]

Displacement in cu in.

Cubic inches of space, which hyd fluid will occupy.

One complete revolution will pump the cu in of fluid from the pump..

 

[patp744]

Displacement in cu in.

Cubic inches of space, which hyd fluid will occupy.

One complete revolution will pump the cu in of fluid from the pump..

So the larger the cu in. The more fluid I have to move through the motor to achieve the motors stated rpm and torque numbers . ?
And I'm guessing that leads back to the size of the pump and what it's out put is ..

Witch leads back to the hp of the engine. .
And I'm sure I now need to know max rpm or operating rpm of said engine. .

Being new to building a hydraulic system ,please forgive me , but is there a pressure limiter that can be put on the system..say it's set at 1800 psi ,and no matter what rpm the engine is running , the drive system will not go above said pressure? ?

 

[J_J]

That is correct.. It is called relief pressure and the purpose is to protect the pump.

The pump is HP limited and the volume will determine the speed of the motors.

 

[patp744]

Speed of the motors?
So a motor that's 7.8 cu in well move faster than than a motor that's 2.7 cu in ?

Or let me ask it like this ..is there a direct correlation between cu in and motor rpm?

 

[aczlan]

Torque (on the motor side) is a combination of function of pressure and cu in (think of it as a breaker bar on a nut, pressure is how hard you are pushing on the bar, cu in is how far out from the pivot point you are pushing).
RPM (on the motor side) is based on flow (GPM) and the motor cu in (ever spin a computer fan with a air blow gun?, the closer to the center you blow, the faster it spins (cu in), the more air you use, the faster it spins as well (GPM).

Aaron Z

 

[aczlan]

Speed of the motors?
So a motor that's 7.8 cu in well move faster than than a motor that's 2.7 cu in ?
Or let me ask it like this ..is there a direct correlation between cu in and motor rpm?

Yes there is a correlation, the larger the displacement, the more flow (GPM) needed to spin it (displacement is how much fluid is needed to spin the motor all the way around one time).
Take a look at the calculators on the Surplus Center site: Surplus Center
With 5GPM, a 2.7 cu in motor will spin at 428RPM. With the same 5GPM, the 7.8 cu in motor will spin at 148RPM.

Aaron Z

 

[patp744]

Ok..wonderful stuff...
Thank you ..
Now how dose torque factor into this ?
I'm guessing that the lower the cu in the more torque?

 

[J_J]

You want as much torque as you can get.

The torque is almost constant throughout the rpm range.

 

[patp744]

Ok..so numbers to watch
Gpm,psi,and rpm. For the pump
Cu in and torque , for the motor.

 

[patp744]

Umm..crap...
What style pump would be good for this application?
Gear , vane, piston ? ?

 

[bigdeano]

I'm guessing that the lower the cu in the more torque?

You have it backwards. The bigger the cubic inches of the motor the more torque it will produce.

 

[patp744]

You have it backwards. The bigger the cubic inches of the motor the more torque it will produce.

Ok.thanks