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 ?