Hydraulics novice after advice

[farlet]

Hello there

I want to make myself a micro tracked timber skidder from scratch. I am totally happy with the mechanical part of the build, but hydraulics are a new area to me.

Details of the build are as follows :

10hp Chinese diesel engine driving the pump
Main drive wheel on the tracks 24" diameter
Total machine weight 400kg
Desired top speed 6-8 mph (About 100rpm on the shaft I think)

Basically I was wondering where the **** do I start ? Questions I have are :

What size pump and motors would work for this setup ?
How do I know how much power it would put down through the wheels ? ie. would it pull the skin off a rice pudding ?

Any help on this would be greatly appreciated. If I have left out any obvious information, let me know and I will post it up. I will post up pics of the build as it progresses

Thanks

Tim

 

[oldnslo]

Not to ruin your day but with hydraulics you will lose around 15% of your input HP minimum so with 10 HP in you may get 6 or 7 to the track. This does not include any mechanical losses either.

I believe there have been a couple of other tracked skidders being built so possibly try doing a search for them.

As for where to start:

You will need to figure the torque required to turn your drive wheels at the load required.
You have already estimated top speed of 100 RPM

Using this torque you can then start figuring Hydraulic motor size required to develope said torque.

Once the motor size is known you can now figure the pump size required to drive the motor at 100 RPM.

I am attaching a sheet with some hydraulic formulas.

Roy

 

[farlet]

Hello and thanks for the answer.

I guess this is where the problem is for me as I have no idea how to work out the torque required. If I am reading it right, 7 hp at 100 rpm is about 360ft/lbs at the wheels. This seems like quite a lot to me.

Also, am I right in saying that if you half the rpm at the wheel, then you double the power up ?

Does anyone know if this sort of torque figure will be any use for pulling ?

 

[oldnslo]

Farlet,

Using your 10 HP motor you can develope approximately 15 GPM @ 1000 PSI

Figure 7 GPM for each drive motor to allow for ineffeciencies this would drive a 16 CIR (Cubic inch per Revolution) motor at 100 RPM.

A 16 CIR motor at 2500 PSI will produce around 6400 in-lbs torque

At 2500 PSI your 10 HP engine will produce around 6 GPM

Again allowing for losses figure your 16 CIR motors will turn at around 30 RPM max

THese numbers are all theorectical and will vary depending on the efficency of components.


A hydraulic motor will only provide increased torque with increased pressure. So at 50 RPM you will have the potential for increased pressure which equates to increased torque.

 

[farlet]

Thanks again for the replies, its starting to make more sense to me now. I think that I will have a go and put a rough prototype together and see what it will pull, then once this is OK, build a proper machine. I am happy for it to go slower if that is the price for more power.

I will keep this thread up to date with some pics and specs of everything I am using.

Thanks

Tim