Hydraulic drive questions.

[szki272]

So I am trying to build a hydraulic drive system using some parts I have. Trying to figure out pump and motor size. The axles have approximately 30 inch tires with 5.13 gear ratios. Would prefer to direct drive the pinions, So 2 motors connected together I am thinking for true 4x4 I would need to plumb the outlet of one to the inlet of the other. By doing this I am not increasing my pump displacement so it is calculated out as one motor? Likely going to use a 22 hp motor or (less likely) a small 4 cylinder I have that is about 60 but it is a car motor so no governor so Unsure how that would work. I have been noticing most systems like this are either using fixed displacement pumps and a control valve some are using a variable flow control. others are using a variable displacement pump. Seems the largest Variable displacement pump from surpluscenter is about 10GPM. Years ago I found all this info online somewhere now I can't seem to find it now. I am sure there is more info needed so ask the stuff I forgot.

 

[dfkrug]

To size your hyd motor, figure out what RPMs you want and work back to the pump(s). A
really slow motor that is direct-drive as you want, will be large displacement, and quite
expensive. To get around that cost, you can go with a smaller motor and gear it down
with sprockets/chains.

You also need to decide if you want one pump or 2 independent ones. HST drive
is the nicest, but costs more than trochoid type.

An inexpensive way to design your own crawler would be to use one motor, one
pump, and a differential axle. Then you can turn by brakes on the 2 sides.

Surplus Center has the hyd calculators for motor displacement and speed.

 

[szki272]

Looking at doing a steering axle or more likely articulated. Saw the cadtrack loader. But figured I wanted to use axles I already had. I have a Transfercase but that means drive lines figuring out where to fit the T case. I figured if they can direct drive. I should be able to run thru a 5 to 1 reduction and get away with a similar or smaller motors.

 

[dfkrug]

I totally relate to trying to design around what you have. I do that when I can as well.

Or I design around what I can obtain cheaply.

Direct-drive is great. Depending on what your pump strategy will be, you will prob be
running the motors independently, or in parallel, not series.

BTW, I built the CADDigger shown in my avatar back in the mid 90s. Very useful and rewarding
to build. However, I now really want track-drive for what I want to do.

So, I have purchased and will pick up this week, a <1ton crawler-excavator. Unlike its bigger
bros, it has directly-controlled spool valves, instead of pilot-operated spool valves, and it uses a single
gear pump instead of duals, or variable-piston pumps.

 

[szki272]

I know what you mean. I have a magnatrac 5000 hydro. It is poorly designed using a 2/1 then a 4/1 chain reduction. The chains aren't oil bathed so they can be a problem. They are difficult to service as well. The motor pump is a fixed displacement as well as the drive motors so it is go or stop. Nothing between. The worst part is the tracks. It is duel chain so it gathers mud. the track frame is a box so drive in the mud and the tracks are full. Then you exert most of your power just circulating mud in the tracks. Part of the reason for wanting a tire machine. I am figuring a little more cost in motors less maintance prone parts down the road to work on.

 

[dfkrug]

I have heard of, but never seen a Magnatrack. They were often advertised in Popular
Mechanics, IIRC.

Could you feather the drive valves for some speed control?

 

[szki272]

you could feather the drive valves for some speed control a little bit. However you were pretty much doing it by restriction of the flow and would lug the motor. It is really slow so it usually didn't matter. Video playlist of the magnatrack. magnatrac - YouTube

video picture of the loader start (axel shortening) Using suzuki samurai short side shafts. Mini loader - YouTube