Question on PT drive function under slippery conditions

[m5040]

On the gas engine machines (esp PT180), if your operating in slippery conditions or if you raise the front wheels off the ground with the bucket, does the rear axle still drive 100%? Or do you notice a drive reduction when one wheel slips or wheel(s) off ground? I hear the older models where plumbed in a way that if one wheel was off ground or on ice, only that one wheel would drive.

We have all seen this

Power Trac PT180 with bucket - YouTube

 

[m5040]

No comments?

 

[joshlee]

I know your asking about the gas machines, which I don稚 have. But, I do have a PT 1430 and it drives with only one wheel in the front, while at the same time driving one in the rear. If the front wheels are off the ground, I?m not shure if the rear wheels drive 100% ?

Josh

 

[Rustyiron]

^^^^^ so in other words, there's a drive motor on each (conventional) drive axle that has an open differential?
I have become curious about the PT machines due to the guys here on TBN with them and their devotion.

 

[Joe Malovich]

It's my understanding that a front motor and a rear motor are in series which means fluid must flow through one pump before the other, typically sharing the load and pressure drop in the line. If one motor has no load then the rear motor sees 100% of the load while spinning at the same RPM. I don't know if they are plumbed in a cross-fashion like your car's brakes or not.

Disclaimer this is what I've read elsewhere, possibly relating to steiners and ventracs, I don't own a PT.

 

[m5040]

Great, that is what I was hoping for. It appeared the PT180 in the video was able to drive with the front axle light loaded or off the ground. I was told that the older machines would loose all traction if one wheel was raised, like they were plumbed in parallel. (One reason I didn't go for that used red 425, since it was around a 1990 model and was expected to operate that way).
Just for thought, Moffett fork trucks are hyd drive and would loose all traction with one wheel spinning, but they have what they call a differential lock, which is basically a flow divider, equally to all three wheels. If someone wanted to install 2 valves on a PT and go straight, it would act like locking axles. Don't know how much you guys get stuck, it would be good to have and really not that expensive (when you compare to installing lockers in a differential).

 

[joshlee]

That is interesting. That differential lock would be nice at times when my PT is in a bind where one of each of the front and rear wheels is off the ground. Those wheels that are off the ground spin and the machine does not go anywhere. Having said that, I could always, so far, get traction by turning the steering wheel or using the FEL in some way to get better traction.

 

[MossRoad]

There are no differentials. There are 4 wheel motors, one at each wheel.

The left front and right rear are in series.
The right front and left rear are in series.
That makes two wheel circuits.
The two wheel circuits are hooked together in parallel.
This is so the machine can turn.

If you're not moving, and you turn the steering wheel all the way to the left, the two left wheels will roll TOWARDS each other as the two right wheels will roll AWAY from each other.

The front left will roll backwards, as will the right rear, and the left rear will roll forwards as will the right front.

Various forms of this movement happen wether you're standing still, moving forward, moving backward, varying speed, etc...

The series and parallel circuits all work in unison.

If a wheel loses traction, the opposite corner wheel will still move the machine as long as it has traction.

If you lose traction at both the left front and right rear, that circuit will get full flow and you'll stop moving, because it is a parallel circuit to the opposite circuit.

Series uses the path of most resistance.

Parallel uses the path of least resistance.

With that said, I've never, ever, been stuck in 18 years of abusing this machine. Even deep snow I've always been able to just drive forward and backwards and drive out. I have had to do the wiggle, waggle with the steering wheel a few times in mud, but that's about it. Always got out.

I did drop off of a hidden log like a ski jump probably a good foot in diameter going down hill in thick brush and high-centered the machine one time. I could not push the brush hog down far enough to lift myself off the log.

 

[MossRoad]

I forgot that I also dug a hole so deep a few times that I dropped the front wheels in and couldn't back out, so I used the bucket to push myself out.

 

[m5040]

Sounds cool and logical to be soft on turf, but that raises my concern about when you use down pressure on the loader bucket to make a cut or to back drag, if the front axle gets light or raises, the machine stops due to the X pattern and both front wheels would spin. Guess I will try one out eventually at Tazewell.

 

[joshlee]

Thanks for all that info Moss. That clears allot up about the way these wheel motors work. Awesome post!

 

[MossRoad]

Sounds cool and logical to be soft on turf, but that raises my concern about when you use down pressure on the loader bucket to make a cut or to back drag, if the front axle gets light or raises, the machine stops due to the X pattern and both front wheels would spin. Guess I will try one out eventually at Tazewell.

For clarification, there is no front axle.

I used to back drag baseball diamonds that were hard, crusty moon dust (granulated limestone). I'd raise the front wheels off the ground and back drag all the way across the diamond using the straight edge of the large light material bucket.

Just be aware, that the PT425 with a fat man on it weighs just 1500#. You only have 750 on the front edge, spread across 48". That's only about 15.7 pounds per inch of blade width. It doesn't take much to stop the machine in that regard. Loose material is no problem.

Now if you get a toothbar, or purchase PowerTrac's rock bucket with teeth, there's 7 teeth. That's 107 pounds per tooth edge. The teeth come blunt from the factory. I sharpened them with a grinder. It made all the difference. 107# on a pointy tip does real well breaking up hard soil.

 

[MossRoad]

And I do not take credit for sharpening the teeth. Someone else on TBN in the PT forum told me to do it. I retreat that I forget who. Fourteen, perhaps?

 

[m5040]

I believe that are two front axles, a right and a left, which are component parts of the wheel motors. When I throw these terms out, I assume that it is taken in the general sense so as not to have to type excessively and be specific. Like differential, although there are no traditional gear differentials like a motor vehicle, there are devices (or engineered paths of hydraulic flow) that allow a differential in speed between the tire/wheels when making turns or even actual tire diameter variances. If you took out the differential in your pickup truck, would you be taking out the axle assembly, the pumpkin (carrier), the ring and pinion or just the spider gears? As describe in the cross pattern hydraulic flow example for the wheel motor circuit, if the front of the machine was raised off the ground, the two front drive motors would have no resistance to motion and thus all the hydraulic flow would cause them to spin, with no flow-torque-motion at the rear motors. The machine stops. It would need a flow divider valve that splits the flow to that circuit and sends (somewhat) equal flow to each motor (like a limited slip or locking gear differential). More hydraulic flow goes to the motor requiring the least torque to move, whether the wheels/tires on the outside arc of a turn or spinning on ice. I sure hope there is a hyd circuit diagram in the owners manual.

 

[MossRoad]

I believe that are two front axles, a right and a left, which are component parts of the wheel motors. When I throw these terms out, I assume that it is taken in the general sense so as not to have to type excessively and be specific. Like differential, although there are no traditional gear differentials like a motor vehicle, there are devices (or engineered paths of hydraulic flow) that allow a differential in speed between the tire/wheels when making turns or even actual tire diameter variances. If you took out the differential in your pickup truck, would you be taking out the axle assembly, the pumpkin (carrier), the ring and pinion or just the spider gears? As describe in the cross pattern hydraulic flow example for the wheel motor circuit, if the front of the machine was raised off the ground, the two front drive motors would have no resistance to motion and thus all the hydraulic flow would cause them to spin, with no flow-torque-motion at the rear motors. The machine stops. It would need a flow divider valve that splits the flow to that circuit and sends (somewhat) equal flow to each motor (like a limited slip or locking gear differential). More hydraulic flow goes to the motor requiring the least torque to move, whether the wheels/tires on the outside arc of a turn or spinning on ice. I sure hope there is a hyd circuit diagram in the owners manual.

That's not how two motors in series in a hydraulic circuit work.

 

[MossRoad]

^^^^^ so in other words, there's a drive motor on each (conventional) drive axle that has an open differential?
I have become curious about the PT machines due to the guys here on TBN with them and their devotion.

No. There are 4 wheel motors and no differentials. Everything is done with hoses and connectors hooked through various series and parallel connections.

 

[MossRoad]

Another thing to mention is that if you have something like the bucket, or blade on the machine, you can easily lift both front wheels off the ground with down pressure. If, however, you have a mower or brush cutter on the machine, and you put down pressure on it, you'll most likely lift only one wheel off the ground, because the decks have rotation built into the roll axis, and the machine has rotation built into the roll axis as well, referred to as oscillation.

The machine by itself articulates left and right on the horizontal plane, and it also oscillates on the vertical plane up to 12 degrees in each direction between the front and rear halves. It keeps more wheels on the ground more often.

 

[Rustyiron]

Thanks Moss. I thought there were 4 drive motors, you cleared that up.