homemade tractor project

[dfkrug]

I am curious why my neighbors HST tractor has a clutch that you press in before starting. What about in cold temps? I would prefer a clutchless setup if possible.

The clutch is for a start-safety, like you car has, if std trans. Also, your
PTO disconnects with the clutch. And finally, you need it to assist in
switching gear ranges or the MFWD in the gearbox.

My CK30HST has the start-saftey feature in the clutch pedal, but I
disabled the switch. Starting an HST tractor "in gear" is not a
danger, as it is with gear trannies. (Exception: if your PTO is engaged
and connected to some implement.) Some HST tractors (e.g. my old
JDs) don't have a clutch pedal, so they require more complicated
electrical and mechanical safety switches.

 

[aspenelm]

Have you also considered an hyd motor at every corner? This is how the
CADLoader from CADPlans works. You can find blders of that machine
on places like machinebldrs network. They have worked out the control
issues, too. The hydraulics are quite a bit of $.

I have seen those CADtracs, they look nice, but I thought they would be a bit harder to put together, slow speeds, and a bit more expensive due to additional hyd motors. By using truck parts the driveline is easily repairable and cheap. I am trying to keep it as simple as possible while still meeting my design criteria.

 

[aspenelm]

I may be getting in over my head on the hydraulics. The numbers below are just for the drive pump and motor, I did not factor in any losses or consider a charge pump. Using some equations I found online, I put the numbers into a spreadsheet and came up with the following:

First I calculated drawbar pull, with 8000 gross combined weight (3500 tractor + 4500 trailer worst case), 30 degree slope, and .1 rolling resistance = 4800 lbs drawbar pull required

This leads to hydraulic motor torque of 5300 in-lbs (450 ft-lbs) after factoring total gear reduction (13.8 ratio) and tire size (31").

Picking a speed of 4 mph for the worst case going up a hill, results in hydraulic motor speed of 600 rpm.

So far, everything looks reasonable to me. Moving on to sizing the motor and pump.

To determine motor displacement; the motor torque, the operating pressure differential accross the ports of the hyd motor, and the hyd motor hydraulic/mechanical efficiency need to be known. I do not know an appropriate number for the operating pressure differential, I would assume that most of the pressure is converted to rotary motion, so I used 2800psi differential (in 3000psi system). I am sure I am wrong here. With motor torque of 450 ft-lbs and .92 eff, this results in 13.15 in^3/rev displacement.

Hyd motor GPM using displacement, shaft speed, and efficiency results in 37 GPM.

Hyd pump displacement using the required GPM, pump shaft speed of 2000 rpm, and .92 efficiency is 4.65 in^3/rev.

Then lastly, the hp required by prime mover, assuming 3000 psi system, the above pump displacement and pump shaft speed, with 0.85 efficency results in 83 hp. This does not take into account any other hyd pumps.

Can someone enlighten me on the pressure differential for the hyd motor ports?

Am I making some gross mis-assumptions?

I will try another vendor sizing guide and see if the numbers are the same.

 

[aspenelm]

Disregard my previous post, can't seem to edit or delete it. I am looking into either all mechanical setup or a diesel electric. Latest design in sketchup.

 

[chad22]

I know this thread is around 5 years old. But I have had a project like this in mind.

I have some of the stuff needed. I have an engine, transmission, rear axle and drive shaft.

If I build it. It's gonna be an automatic transmission.

The plan is to use the engine out of my truck. It smokes a bit and needs an overhaul but should work for awhile on the tractor. I have another engine I'm putting down into my truck. So no problem there.

With this setup. I can have a cheap tractor with cab, heat and ac. I think this is the only way I'm gonna be able to afford a tractor, especially if I want ac and heat. lol

And another thing. I'll know it was made in the usa. Because I built it. :thumbsup:


Ps. That is a nice sketchup. I have have saved to work off of.

Chad