Wheel motors for forwarder

[MossRoad]

OK, but if you allow them to travel at different speeds, wont it loose traction when one wheel either lifts or has no grip ?

No. Think of it this way...

If you have two or more wheel motors in series and they're driving along and all of a sudden one gets lifted off the ground or spins in mud what happens?

As that 'loose' wheel motor tries to spin, it cannot draw more hydraulic fluid through the motor behind it, nor push more fluid through the motor in front of it because it has no load. The other motor(s) that is(are) not losing traction will immediately build pressure and keep turning.

Or something like that.

My machine has 4 wheel motors and is articulated in the middle.

The left front and right rear wheel motors are in series.
The right front and left rear wheel motors are in series.
Both of those series circuits are in parallel with each other.

When you articulate the machine to the left, for example, the two left wheels roll towards each other and the two right wheels roll away from each other.

So if you think about it, as you turn left, the left front wheel and the right rear wheel are rolling backwards as the right front wheel and left rear wheel are rolling forward.

If you want 6 wheel motors, three to a side, and you want a pivoting axle, you're going to have to account for that somewhere. Same as if you want it to articulate.

Make sense?

 

[ptsg]

Is getting 3 differentials an option? I suppose at least the 2 rear ones would need diff lock, ideally the 3 would have it. Or two differentials if you use a bogie axle setup on the rear. That way, you could connect all motors in series.

You're looking to build a forwarded similar to the Kranmann's ones right? Like this:

 

[farlet]

Thanks again, good info and I am starting to understand a bit better. Yes it is just like the Kranman machine I want to build but with all 6 wheels equal size. I could build it with differentials and this would be much more within my skill set as I have built several competition offroad trucks. I think if I end up going down the differential route I would just do a conventional automatic transmission and 4wd transfer case and ditch the hydraulic drive idea. I just like the simplicity and robustness of a hydraulic wheel motor at each wheel, but maybe I am kidding myself.

I can build the swinging axle with a chain drive inside it and then it would only need 1 motor to drive the 2 wheels, but I dont know if that helps the situation !

 

[oldnslo]

You will find the hydraulic drive to be very inefficient compared to automatic transmission and differential with differential locks.

A good hydrostatic drive is around 85% efficient under the best of conditions and would probably cost more than mechanical drive.

Might be an option for hydraulic motor driving conventional differential vs u-joints and drive shaft in the pivot.

 

[MossRoad]

Something you're going to find if you go the 6 hydraulic wheel motor route is there's a compromise...

You'll have to size the motors large displacement enough to give you good torque for heavy loads, hills and such, yet size them small displacement enough to get good top speed if you're interested in going anywhere of any distance. Since the variable volume pump can only supply X gpm at Y pressure, you have a one speed transmission. You'll have to compromise on top end speed VS low end power.

If you go with automotive differentials, you could drive them with hydraulic motors, but again, unless you have some really expensive hydraulics, you're going to have to compromise on top end speed VS low end power.

If you go with a transmission, driveshafts, and differentials, you resolve all of those issues, as you can select gears, or even ranges of gears, depending on how you go.

Just some things to consider.

Also, why reinvent the wheel? Use a design of someone else that works well and make your own copy if you're set on building it yourself.

 

[farlet]

Thanks for the input from everyone. I think that I will ditch the hydraulic drive idea. I already have the gearbox and transfer case to suit the engine so I think I will go this route instead. I will put a build thread up once I get started with it. Thanks again

 

[Dennis59]

I am going to build myself a timber forwarder with crane. It is going to be 6 wheel drive and I would like it hydraulically driven. I am thinking of using these for wheel motors : Silnik hydrauliczny BMR chłonność: 200cm3/obr obroty: 300obr/min z łożyskowaniem do rębaka

I am after some advice on a pump for this and also how you plumb up 6 motors like this. Do you plumb them up in series ie. feed goes into the first motor and then out of the first and straight into the 2nd, and so on. I need all 6 motors to turn all the time. Engine will be a 2.5 litre turbo diesel with around 110hp

Also, is it necessary to have brakes ? I cant see how the wheels can turn if there is no flow of oil in either direction.

Any advice will be greatly appreciated, if you need any more info, just let me know

Thanks

I think you are asking for a lot of headaches. You would be better of taking a hydro pump and drive motor from a salvaged combine along with the oil cooler and hook it to a standard truck transition with a transfer case and use independent diff locks. (look in to how the guys build rock crawlers)

 

[Shenandoah MF1760]

Without diving into all the other engineering aspects, using a wobble plate hydraulic pump would give you variable speed and reversibility. Depending on the pump the neutral position might require brakes.