Traction Hydraulic wheel motor question

[CreativeGuy]

Well, I managed to get Artie (PT425) stuck the other day. I was dumping some dirt and there was a really soft spot under the left front wheel. When I went to back up, the left front wheel dug itself into a hole and the right rear wheel came off the ground. I couldn't go forward as i was at the edge of an embankment. I'm new to hydraulic wheel motors so I don't understand why the right from wheel didn't turn when I tried to go in reverse. (the left wheel was spinning away) Is there some sort of traction control sending fluid to the wheel that has the least resistance?

I was abel to move forward enough to get out of the hole which I filled with gravel and then dug out the excess earth on the right side.

Guess I have to start working on getting a degree in fluid dynamics.

Cheers and thanks in advance for your responses.

Steve

 

[John Fitzgerald]

It has a differential. It's supposed to work that way. The wheel with the least traction spins. If you have a locking differential, then both wheels try to pull equally regardless of traction.

 

[BobRip]

The one with the least traction will slip but the opposite corner will get that flow so there is some torque loss, but you still have torque on the other wheels. I have found that when I get stuck if I turn the steering when left and right the side walls will get some extra traction and sometimes I can get out. It kinda walks out when I do this. Mostly use for going up hills that are too steep for motor torque. Try it and see. Couldn稚 hurt. There is no differential in this hydraulic tractor.

 

[MossRoad]

It has a differential. It's supposed to work that way. The wheel with the least traction spins. If you have a locking differential, then both wheels try to pull equally regardless of traction.

It does not have a differential.
It has four hydraulic wheel motors, one at each wheel, connected in a series/parallel configuration.

 

[MossRoad]

Usually, you can dump the bucket to vertical, push it down into the soil so it lifts the front wheels off the ground, push the reverse pedal slowly while curling the bucket and move backwards enough to get the front wheel out of the hole. Set down and repeat. In simple terms, use the bucke to push you backwards.

However, you mentioned dumping over an embankment, so your bucket probably had nothing to push down on anyway.

As I understand it:
- the left front and right rear wheels are in series(one in-line with the other), forming a circuit I'll call A.
- the right front and left rear wheels are in series(one in-line with the other), forming a circuit I'll call B.

-The variable volume pump provides FLOW to the wheel motor circuits. NOT PRESSURE.
-The pressure is developed at the wheel motors, not by the pump.

-The pressure is developed when the flow hits resistance.
-The resistance in circuit A, in this case, would be your left front tire against the dirt, and your right rear up in the air resisting nothing.
-The left front is spinning due to loss of traction, not due to loss of pressure or flow.

So why didn't the right front tire and left rear tire pull you out?

-Circuits A and B are connected to each other in parallel (side-by-side).
-Hydraulic oil takes the path of least resistance.

Once a wheel motor in circuit A starts spinning, that circuit becomes the path of least resistance and all the flow starts flowing towards circuit A, away from circuit B.

The more you spin the left front tire, the less flow will be available to the right front and left rear wheel motors.

Let off your foot pedal.

With very minimal reverse foot pressure, as Bob mentioned, turn the steering wheel lock to lock left and right, and you almost always can wiggle your way out of a stuck situation. It may take a while, but most times it will walk its way out. In 17 years, I've only been stuck one time, and that was when I drove over a hidden log and dropped both front tires over the log, and left them a few inches off the ground and the log holding up the tractor in space. Chainsaw to the rescue.

Do you have an owner's manual with the hydraulic schematic?

 

[MossRoad]

Here's a good video that explains flow and pressure... a very good video.

 

[John Fitzgerald]

It does not have a differential.
It has four hydraulic wheel motors, one at each wheel, connected in a series/parallel configuration.

Sorry, my bad.

 

[MossRoad]

Sorry, my bad.

No problem. These Power Tracs are not "normal" machines. :laughing:

 

[ponytug]

I got mine stuck once in the first few hours of use, too. Then I learned the wiggle and the trick of using the FEL from folks here, and I haven't been stuck since.

I rototill a terrace, our garden, every year, and there is a greed / fear dynamic. I want to till as much as possible, but I fear that the soft bank will slide out from under the PT. So far, I haven't tipped it over the edge, and I have been able to unstick the tractor by pressing down on the tiller and pushing myself out. Pucker factor...high. Somehow putting in a concrete retaining wall hasn't made it to the top of my do list, but it is getting there.

Welcome to the stucker club!

All the best,

Peter

 

[CADplans]

It has a differential. It's supposed to work that way. The wheel with the least traction spins. If you have a locking differential, then both wheels try to pull equally regardless of traction.

It does not have a differential.
It has four hydraulic wheel motors, one at each wheel, connected in a series/parallel configuration.

I guess I have to disagree and say the machine in fact does have differentials.

A differential can be constructed in several ways,,,

Here is a test that can demonstrate that the PT has differentials;
With your pickup truck in park (automatic transmission), jack both rear tires off the ground.
Rotate one rear tire,,, note that the other tire will rotate in the opposite direction.

Now, lift the front tires of the PT off the ground with the bucket,, then rotate one tire.
The other tire, like the differential equipped pickup,, will rotate in the opposite direction.

The PT is equipped with hydraulic differentials.

Back in the 1960's, some cars had a "posi-traction" rearend.
In those cars, you could not rotate one tire forward, and cause the other to rotate in reverse.

I was never able to see in one of those,, but, they were a BIG problem, after they were a couple years old,,
clutches refused to slip,, the car would "hop" when going around a corner,, like an ATV does today.

My pickup has a locking rearend,, it will forward-reverse rotate the tires, as long as you do it slowly.
Speed the rotation up too much,, the differential will instantly "lock",,

I am getting off base,, slightly,, but,, the PT DOES have differentials,,, IMHO,,