Wheel motors for forwarder

[farlet]

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

 

[oldnslo]

What will be the total weight of the forwarder empty and fully loaded? Reason for asking is will the 6 motors have enough torque or will you require some gear reduction or gearboxes the motors connect to.

Will you be using hydrostatic drive pumps or variable volume pumps with direction valves for control of speed and direction?

 

[farlet]

Thanks for the answer. It will be around 1200kg empty and around 5000kg fully loaded. Tyres will be 780mm rolling circumference. I would take all guidance with the pump, I havent bought anything yet. I was reading last night and it seems that you can plumb the motors through a series of diverter valves so you can operate them in series or parrallel effectively giving two speeds

Thanks

 

[hayden]

Neat project. I hope you will post progress along the way with lots of pictures.

As for the drive hydraulics, I think you have a lot of calculating to do to get it right so it works as desired. Here's how I would go about it.

- You have 110hp to start with, but let's derate it to 100 hp to allow for hydraulic losses. So you have 90HP available to drive the forwarder.

- You will first need to decide what the steepest incline is that you need to climb. Then you need to figure out the power required to move the forwarder up that incline, at various speeds when fully loaded. From that you can see what speed you can get with your 90hp. That's the speed you need to gear for when delivering 90hp to the wheels.

- "gearing" is a combination of tire size, gear reduction ratio, and motor displacement. You want the oil flow and pressure consumed by that combination to match the max flow and pressure of your pump at max power of 90hp.

- From the results of the above, you can calculate the speed range of the forwarder. If it's too slow for more level ground, then you will some sort of variable displacement pump or motors, or a series/parallel valve system, or other way to have multiple speeds.

It's a lot of calculating, but worth the time to end up with something that works well.

 

[oldnslo]

Will this have front axel steering or center pivot steering? Either way you need to determine how you will control motor speed to each axel to allow inside tires to slow and outside tires to speed up.

Hydrostatic drive like a skid steer will provide the most efficient type of travel drive and provide hydraulic braking but again a bunch of calculations need to be performed to confirm that you can control that load on the desired slopes.

Down side of hydrostatic drive is those pumps are now dedicated to drive system only so you would need separate pump(s) for loader.

Yes there are options for flow divider to split flow to the drive wheels for series or parallel operation

 

[farlet]

It will be pivot steer. I dont want different wheel speeds, I want to have them as if the diffs were locked all the time. It will only be used offroad in the forest. I was assuming that I was going to have multiple pumps so this is no problem. The engine I have already has a power steering pump so I figured use that for steering, then have a pump for drive and a pump for the crane/winches, etc...

My terrain is quite steep in places I guess up to 35 degrees where we might be driving

Thanks for your help, I am happy to pay for some advice if it is time consuming to calculate everything

 

[oldnslo]

With differential locked it will be very hard to steer since all the wheels want to travel at same speed.

This is based on operating a center pivot 4 wheel drive farm tractor with diff lock

 

[farlet]

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

 

[oldnslo]

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

Yes if you allowed all the flow to go the wheel that lifts. How where you going to keep flow split with all wheels driving same speed? If in series use then you effectively have the same torque as running a single motor of that displacement since pressure is divided across all the motors in series.

 

[farlet]

I am probably demonstrating my lack of knowledge on the subject ! I dont have any knowledge on how to split the flows and generally how to connect this system up, hence asking for advice. I dont even know how to work out how much torque is required to move the machine forward and backwards. It will only be used around my own property, but we have 300 acres so we do need to travel around the site, so I am guessing if it would do around 8mph top speed that would be good, but most of the time you would be going slower than that over the rough terrain. We are going to use a 31 15.50 15 tyre on all 6 wheels so it will have a lot of flotation and grip.

In an ideal world how would you set this system up ?

 

[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.