hydraulic riding mower project

[Santos89]

Hi everyone!.

I have a project in mind. It consists of converting a MTD riding mower to hydraulic transmission, using a 12hp engine, an oil pump and one or two hydraulic engines. my idea is to drive one or 2 hydraulic engines with the oil pump and drive the pump with the 12hp engine. But I am a complete rookie at hydraulics so I need some assistance. The mower weighs 660 pounds with me on it and it has 18.5" wheels. I made some calculations and i found out that I need the wheels to spin at 260rpm in order to reach the max speed of 15mph (am i right?). So my question is: what gear do i need? is a 12hp engine enough for my project?

My aim: get the MTD to reach a max speed of 15mph (unattached) and still be able to tow a 600lb trailer (loaded trailer).

THANKS A LOT!!.

 

[J_J]

12 HP is not going to do a whole lot for what you want.

They probably already make a hydrostatic mower/tractor that will run at about 8 mph. and you want to run at 15 mph, pulling yourself and another trailer with 600 lbs on it, using hyd motors.

That engine can only pump about 7 GPM, using a .4 cu in pump running at 3600 rpm

A hyd pump pumping 7 GPM at 2500 psi will require 12 HP

7 GPM and a hyd motor with 6.2 displacement = 260 rpm, and at 2500 psi, the torque would be about 2468 in lbs, or 205 ft lbs.

Then you will need control valve, hoses, fittings, fluid, etc

http://www.surpluscenter.com/item.asp?item=13-1489&catname=powerTrans

http://www.surpluscenter.com/item.asp?item=13-1474&catname=powerTrans

 

[Santos89]

Thanks a lot J.J.!.

I am sorry for the misunderstanding, I don't pretend to do 15mph WITH the trailer ATTACHED, that would be insane! haha. I was talking about doing 15mph with the mower unnatached (660lbs just the mower and me). I certainly don't expect to do over 5mph with the trailer attached. I know there already are hydrostatic trasaxles (Husqvarna makes a few of its mowers with hydrostatic drive) but i was actually thinking of a hydraulic motor rather than a complete axle.

Surplus Center - 9.7 cu in CHAR LYNN 130-1016-003 HYD MOTOR

I chose that one because I think it has plenty of torque (1000 in-lbs). But as I said before, I am a complete rookie at this. I haven't been able to find a formula on the web that tells me how much torque I need to get the mower moving.

THANKS!!

 

[YZOUTLET]

Hi Santos,

Not sure if any of our pumps will work for you but we got 11 GPM, 13 GPM, and 16 GPM! Check us out at:

Hydraulic Gear Pumps - YZOUTLET

Cheers,
YZOUTLET

 

[J_J]

To pump 12 GPM at 2000 psi, requires about 16 HP.
----------------------2500 psi------------------21 HP.


If you use the 9.7 cu in motor above, it is a 1000 psi continuous run motor, and 12 GPM will turn the motor at about 282 rpm . You would have to regulate the psi to 1000 psi for one motor, or pump 12 GPM through two 1000 psi motors in series.

 

[Santos89]

Thanks again J.J

Just so I know a bit more about this subject, more PSI mean more torque and more GPM mean more speed?
I was thinking about using a single motor to drive an axle (I am looking for the most convenient one that allows me some gear reduction on the axle, 3:1 or 4:1)

this one maybe
Surplus Center - 6.2 cu in CHAR-LYNN 104-1009 HYD MOTOR

I know my engine cannot provide 20GPM at 3000PSI to fully load the motor above but I have the following idea in mind: getting the ideal motor (maybe the motor above, as you recommended 6.2 cu. in.) and a pump that allows me to control both PSI and GPM so I can set the pump to low GPM and the maximum PSI supported (by both motor and pump) when I need torque for towing, and viceversa (high GPM, low PSI) when I need speed. Of course, i planned all this assuming that what I stated at the beginning is true and that the gear I need exists.

What would be better in my case, 2 motors direct driving the wheels or a single larger motor driving an axle?

I really appreciate your patience and any suggestions you might have.

Cheers!

Santiago

 

[Santos89]

Anyone? Is it possible?

thanks.

 

[J_J]

You should know that pressure is developed by the load.

The pressure will vary based on the motors ability to do work.

The motor can be geared down to increase torque, but at a reduction in rpm, and that will affect speed.

If you change pressure, or cu in on the motor, that will affects torque.

I don't know the torque to weight relationship, and if you can figured that out, you will be ahead of the game.

I just don't believe your 12 HP will get the job done.

 

[Santos89]

So, the higher the load on the HYD motor is the more pressure it will get? and a motor with higher torque will handle load more easily?

I was thinking of a single motor driving an axle with a reduction like you suggested (3:1 or 4:1) and a valve to control GPM (high GPM for speed or low GPM for torque).

I am still working on the torque calculations to find out how much torque I need to spin both wheels with the 660lb load.

I had my doubts as well with the 12hp engine, but after seeing several projects carried out with smaller engines (8hp, 10hp) I thought It was possible for me to do this with my 12hp

Recommendations are welcome!

Thanks a lot again J.J.

 

[Santos89]

what are the advantages/disavantages of parallel and series HYD circuits? if I have 2 HYD motors do I need twice the pressure and GPM from the pump?
Thanks