The hydraulic motor has a GPM flow rating of 60. I have a Husco 3 spool valve rated @ 40 GPM I am thinking about using in a closed center configuration. Not quite matched but I think the flow might be adequate for the speeds I intend to operate this machine at -- about 7 miles per hour max I would think. Of course I would still have to look at the circuit closer once I figure out the specs on the Sunstrand pump. Upon closer visual examination of the pump, I was mistaken in stating that the two hydraulic hoses originating from the control valves piggybacked on the pump connect to the small gear pump at the tail. In fact, those hoses communicate with ports at the lower portion of the piston pump close to the base. Some sort of control for the swash plate of the piston pump I'm thinkin'. If tha'ts the case, then the small gear pump can probably be used to run my double action cylinders therefore simplifying the circuitry into two separate systems, main pump for the drive in a closed center configuration as suggested previously, and the gear pump for the cylinders in an open center type control. Your suggestions on the sizing of the control valves and cooling for the fluid are highly valid and appreciated, they will be incorporated in the final design.
With reguard to the power source, depending on the GPM flow of the pump, your point on the use of a transmission intermediate to the pump may be necessary indeed. If the pump flows 40 GPM, a guesstimate on my part, my engine would have output at least 80 HP at 1800 RPM roughly, allowing for inefficiencies. I have the formula somewhere but have not done the calculations on that yet. Can my 283 CI V-8 engine meet this need, I'd have to just try and go at it, dyno testing is out of the question on this low budget project. If not, I'd have to use a transmission to obtain gear reduction.
As to the size of this skid steer project, poster Richard W. was curious. My concept in this home built low budget skid steer assembled with less expensive surplus equipment is as follows:
Compact build out of structural steel, built stout. It has to be maneuverable in my small residential yard.
4 wheel skid steer steering linking two independently controlled wheel motors to their respective rear wheel partner via # 60 or # 80 chain and sprocket drive. I'm still entertaining the idea of 4 wheel steering but that complicates the steering system considerably. The wheels are off of a Gehl skid steer, the nicest aquisition of mine thus far as fas as value.
The loader scoop sized to carry at least 1/2 cubic yard of dirt comfortably. That would that be, roughly 800 lbs. I would think? A little too ambitious?
Stabilizers on the backhoe end 5' long per corner, angle of support adjustable anteriorly and laterally at reasonable effective ranges.
Capable of digging to 5' depth using the backhoe attachment.
Weight? Who knows!
As you can see, I continue to define the parameters of this project and establish the specifics as I go along. This is an exercise in shadetree engineering to be used only by me at my residence in non-mission critical applications. Of course I would like to incorporate the best ideas I can come up with as well as constructive contributions from people like you folks. This is a learning experience I've been excited about for a long time and the process I've undergone so far has already been highly rewarding to my psyche. Thank you for your time and keep the ideas and constructive comments comming!