Question on PT drive function under slippery conditions

joshlee · Jun 23, 2019

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

MossRoad · Jun 23, 2019

m5040 said:
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 · Jun 23, 2019

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 · Jun 23, 2019

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 · Jun 23, 2019

m5040 said:
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 · Jun 23, 2019

Rustyiron said:
^^^^^ 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 · Jun 23, 2019

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.