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32 replies to this topic

#31 skyrydr2 OFFLINE  

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Posted January 30, 2014 - 12:16 PM

Those are some serious numbers for a garden tractor sized unit! One note here is with 2 motors you need 2 pumps or some way to divert flow from one motor to be able to steer. 2 pumps will need almost twice the HP as each pump requires something to drive it. This way you have independent drives for counter rotation. If using a single pump and 2 motors the volume is cut in half so it would be very slow under load. Just some food for thought. :-)
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#32 trowel OFFLINE  

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Posted January 30, 2014 - 06:48 PM

True but that is the neat thing about fluids pumps, there are even planetary types and two stage type also.

The main pump will have to handle the two hydro motors, i have no figures to throw out, just what i know. There are different kinds, gear, vain and piston, the piston type is the slowest and produces the highest torque per sqare inch, gear motors are the most common and can be driven at mild speeds, vain is the fastest, the faster something spins the more GPM it requires, gearing down the motor is another way of using a smaller motor for less GPM and smaller main pump.

Because of the return system hydro requires less GPM then say PSI for air motors which is double to triple that of hydro and without the troubles of air.

Hydrostatic trannys are by and by a big pump driving a hydro motor all built into one compact case.

Weight of the tractor with the tracks weather they be rubber or steel will give a pretty good idea as to the size of the pump needed.

jdcrawler would be the man to ask, he has built similar things before, i might send him a PM if you are thinking of the hydro set up.


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#33 TUDOR OFFLINE  

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Posted January 30, 2014 - 07:45 PM

Two separate systems is a given with using variable displacement pumps or control gets iffy and complicated.

 

The max numbers are impressive, but reality will be something less. A Cat D10 may be able to push dirt around at 4.5 mph. A GT sized crawler will be substantially slower. At half speed, only half of the horsepower can be delivered, or be required. If it needs less than max pressure to travel at half speed, that's another reduction in horsepower required.

 

At a travel speed of 1 mph pushing dirt with maximum hydraulic pressure, maybe 6 hp from the engine. Higher horspower may accelerate it faster to 1 mph, but that also gets the pressure up to the relief setting faster, and there is the limitation.






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