Hydraulic power cart Help

[kameljoe21]

My plan is it build a power cart for my welder set up.
I am having trouble finding the right information.

These are my specs as of right now.
2 wheel drive, one right drive motor on left drive motor.
about 6 foot wide from outside tire to outside tire
8 feet x 4 feet for the deck and over all length will be 10 feet with the last 2 feet to house the motor/pump and Hydraulic Reservoir, filter and a cooler if needed. and controls.
The rig will weigh less than 1000 pounds and total weight capacity will be 2000lbs, for a total of 3000 pounds.
Wheels will be around 18 inch diameter, with a rating of 900lbs or more.

I have sourced out parts, but unsure what I really need

I will be working with a 13 hp gas motor, with a positive placement single stage pump that produces 10gpm at 2000psi. With a flow divider rated at 10gpm.
Horsepower Required to Drive Pump: GPM x PSI x .0007 This come out to 14HP. If I am right.

So far I have read so much about torque. Than I am unsure how to figure it out. I want to size my motors for around 5 mph. I know an 18 inch diamter wheel at 100 rpm at the shaft will give me 5mph But i need to know the torque, In order to move the machine and get the correct size. travel speed: MPH = RPM x wheel dia. inches / 336

To calculate motor torque, multiply the estimated weight of the vehicle by the traction efficiency. (.75) in this case. That is the amount of tractive effort the machine will produce.

Now divide the tractive effort by the number of wheel motors. This is the amount of effort each motor must produce assumimg the machine has equal left-right weight distribution.

Now divide the tractive effort by the inverse of the wheel radius in feet. This is the torque at the wheel hub to generate peak tractive effort.

Now divide that by the reduction ratio of the gearbox driving the wheel set. This is the torque at the motor output shaft in ft. lbs.

Multiply that value by 1.2 to account for dynamic efficiency of the reduction drive and then by 3 or more to provide sufficient torque for slewing.

Now you can cross-check the power of the drive to see if it meets your minimum speed requirement. (Power) 1hp is 33,000 ft. lbs. / min.

This is the best I can find, But unsure of the numbers on this. It is confusing to me.

 

[kameljoe21]

Now divide the tractive effort by the inverse of the wheel radius in feet. This is the torque at the wheel hub to generate peak tractive effort.

This is the part that is giving me the most trouble.
3000lbs x .75 tractive effort =2250
2250lbs /2 wheel motors= 1125 lbs
so if i am right Inverse means opposite of the wheel radius.
circumference of a circle 56.55" 5.71 feet.
1125lbs /5.71 feet circumference =197.022 foot pounds of torque.
or
1125lbs /1.5 feet diamter = 750 foot pounds of torque
or
1125lbs / .75 feet radius = 1500 foot pounds of torque

 

[kameljoe21]

Axle torque in inch lbs: T = F x r
T = troque inch lbs
F = force or draw bar pull in lbs
r = whee radius in inches

f 600 x r 9 = 5400 torque inch pounds or 450 foot pounds torque
Grade resistance: F = GR x W
GR= grade resistance in percent (20% is written .20)
w = vehicle gross weight

w 3000x gr .20 = 600

Now this would be for one wheel if I divide by 2 i come up with 2700 inch pounds torque per motor?
Now i am grossly over stating the weight by a lot of weight.

 

[Rustyiron]

No used Toyota or Nissan pickups out there :laughing:
Just kidding, welcome to the forum and just wait, CJone is a member with lot's of hyd know how and there are other's should be along for the math. I'm no help with this other than being a smart ***

 

[CJONE]

huh? ME, don't know nuttin. For hp required use GPM X PSI + by 1480. That gives you 13.51 EBH. Now here is the issue, you have to derate by 50% because this give you electric brake horsepower. You are using a gas engine and that is 1/2 of a electric motor. The Hondas are on the stout side so my guess you will be in the 1200psi range with that engine at 13hp. My question is, is how are you going to turn it? Not a fan of flow dividers either. You need to control speed AND direction. Myself I would use a differential out of a small pickup or car with 1 hydraulic motor driving the pinion. Use a flow control directional 4 way spool valve, then either steer it with brakes or a mechanical method for the front wheels. The reason you see hydrostats for skid steers is they are speed controlled in both directions F and R. But that is $$$. Once you know how you are going to control steering, direction and speed we can figure out the rest. Your engine is the limiting factor for torque, you have a 5 mph goal so you size a motor/motors for this and the torque will fall in. Here is a example, you have 10gpm a 18.7 cuin motor will give you 120 rpm at 1000psi with 2610 in lbs. Split the displacement and flow and you have a 9.6 cuin at 113 rpm and 1280 inlbs. Let us know on how you plan to steer it and control speed and direction. CJ

 

[kameljoe21]

Edit I am going to use 2 individual directional valves( 5 gpm for each one) . Not spool as they only allow one flow in to them. I am going to control with 2 spool directional valve. Nothing fancy, My small power unit that was an old hydraulic tire machine ran a hydraulic motor forward and reverse with no problems.
Steering is done by slowing one motor down and allow the other motor to move faster, Just like in a skid steer, Hydrostatic motor are way to expensive for what i want to do.
Flow divider should allow for even flow to each motor, this will solve the path of least resistance. I do not want the flow to be dumped in to one motor and the other one not have power.

 

[kameljoe21]

As for control and speed it will be by feel of the directional valve, I have driven skid steers for many years, and many other hydraulic driven machines. One that i use sometimes is a KWIM Sod Installer track machine, They use a similar set up but with a tandem dual pump to 2 drive motors. It is also controlled by a 3 spool valve, right left forward reverse and cylinder up and down. They use a great deal of power to allow for up and down movement while the machine is on the go, with a rated capacity of 2500 lbs and the machine it self weighs around 2470lbs. Fully loaded the thing weigh just under 5000 pounds as my machine will weight less than 3000lbs. With around 27 hp gas motor. This is way more than i need, plus this is a track unit. half of that is 13.5 hp when you consider it only need less than half of that hp to move the machine. the extra is to allow full function of everything while moving.
I do not want to use parts off of other machines, This will be all new parts and materials.

 

[kameljoe21]

.37/0.37 CU IN HYDRO-GEAR PC-MNLL-5T1X-AXXX/TV-QLLT-NLLN-1XBX HYDRAULIC DOUBLE PISTON PUMP
I am unsure how a hydro pump works and if the hp supplied is enough for it to work.

 

[kameljoe21]

0.48/0.48 CU IN DYNAMIC HYDRAULIC DOUBLE PUMP From Surplus center

I was looking at something like this for the pump

for the control, I am looking for a 4 way, 3 position, spring center, open center. valve.
1 SPOOL 20 GPM PRINCE MOTOR VALVE from surplus center
Q:will this control a motor forward and reverse?
A: Yes it will control both directions and allow the motor to coast to a stop when shifted to the center position.
This unit should work for controlling one motor.

 

[kameljoe21]

I have contacted someone at a hydraulic company who will help me build my system and will have a phone call on Monday to discuss it more in detail. I will post more information on it. I hope the information will be helpful for people looking for it.