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Need help with hydraulics
QUESTION:I have always wanted to build a little skid-steer go-kart type thing to play
around with. Something about the size of a riding lawnmower.
I have been thinking of using a gasoline engine to turn a hydraulic pump.
The pump would power hydraulic motors. There would be two motors. One for
the left wheels, and 1 for the right wheels. I would use hydraulic valves
to control fluid to the motors, allowing me to steer by skidding.
However, I know nothing about hydraulic pumps and motors as far as how fast
they can go and what kind of power and fluid they need. Can anyone help me
out? Basically, here are my questions:
1. Is my plan doable?
2. What type of pump and motors would I need?
3. How much HP from my gas engine would I need to power the hydraulics to
be able to run the go-kart at around 15mph or so.
4. How large of a fluid resevoir is required.
5. Is there a way to make the wheels go forward and reverse?
ANSWER: Yes.
You can determine the motors you need to do 15 MPH by calculating what
RPM you need the wheels to turn to achieve that speed. 15 MPH is 22 fps.
The circumference of your wheel is pi*d. So if you use a wheel/tire that's
30 inches tall, it will travel 94.2 inches per revolution (7.85 feet). So it'd
need to turn 2.8 RPS, or 168.15 RPM to achieve 15 MPH.
Now you need to find a hydraulic motor that'll turn about 168 RPM at
a reasonable flow and line pressure. Power in a hydraulic system is a
function of flow and line pressure.
A Char-Lynn 1263755 hydraulic motor will achieve 168 RPM a flow of
12 GPM. It'll deliver 2571 inch-pounds of torque (214.25 ft-lb) at that
RPM with a line pressure of 1450 PSI. That's more torque than you'll
need on level ground in a light vehicle, so you can operate at a lower
line pressure.
A Wagner 531434 pump will deliver 12 GPM @ 2000 RPM. The gas
engine you'll need to power the pump could possibly be as small as
5 hp, but a 12 hp engine would be able to deliver full line pressure
at that flow.
About 5 gallons.
Yes. Hydraulic motors are bidirectional. You just need the proper
control valve. Converta 523621 proportional bidirectional control
valves would do it.
All of these parts are available from Valu-Bilt Tractor Supply
under the part numbers I gave. There are plenty of other sources,
and plenty of other parts, that can do the job. Northern Tool
carries some that would work. Surplus Center has some that
would work too.
The key is to determine the RPM the wheel has to turn to get
the desired speed. Then select a motor which will turn that
RPM at a flow and pressure which is reasonable for the power
requirements of the vehicle.
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