Need help buying a hydraulic motor

[woodlandfarms]

So here is the deal. I may have access to a tiller and a Post Hole digger, all powered by a conventional PTO. The price is good enough for me to consider rigging a hydraulic motor (making them swapable) and using my 3pt adapter... Still have a few things to iron out (how to get the 3pt to work with my system and make a motor swappable) but I don't get the basics.

So looking at Surplus, which of these would be the best motor... And why the one you recommend over the others. They all seem to take the same GPM and Rotate at the same speed, just the cubic inches are different.

Surplus Center

For me it is 3000PSI at 18GPM.

Carl

 

[oldnslo]

Carl,
At the same inlet flow in GPM and the same operating pressure a larger cubic motor will run slower but generate more torque.

It boils down to how much torque and what RPM do you want your equipment to operate at and and what torque.

Roy

 

[J_J]

I believe the rpm's on those motors are to high for a direct driven post hole digger. On some of the hydraulic post hole diggers, they just put a hyd motor on the gear box. The largest of those hyd motors have about 2780 in lbs of torque, and if you reduce the rpm via a gear box to about 150 you should have some good torque.

Some diggers have a 3.18 : 1 So if the hyd motor turns at 600, then the auger would turn at 188 rpm.

Are you trying to turn the auger directly, or go through a gear box? One of the PT guys made himself an auger using a hyd motor, and coupling the two parts with a heavy duty chain. Will try and find a picture.

 

[3238dpw]

Here is the link http://www.tractorbynet.com/forums/power-trac/91387-better-late-than-never.html

 

[J_J]

Thanks. That is the link I was looking for. Gravy did a good job on his auger.

 

[SSdoxie]

I am going to assume you want to attach the motor to the input of the gear box on the tiller and the auger, this would avoid major modification to both attachments. With that you will need to come as close to the 540 PTO speed as possible. These motors you listed are not all the same speed, look more closely RPM speeds are close but constant flow vaires from 17.1 - 19.7 GPM. Here are the speeds of these motors figured at 18 GPM:
4.95 Cu.In = 840 RPM
6.15 Cu.In = 676 RPM
7.63 Cu.In = 544 RPM
9.59 Cu.IN = 433 RPM

Keep in mind the 18 GPM spec you have is at Full throttle, flow decreases with reduced engine RPM. So I see your 2 choices are either the 6.15 or the 7.63 motor. The 7.63 will give you more torque for the tiller, but would require running at full throttle to get resonible speed. The 6.15 motor may work better on the tiller giving you more RPM flexibilty but may run auger too fast even at very low RPM, just off idle. The 6.15 at 1/4 engine throttle would be close to 4.5 GPM = 170 RPM of motor
If I was doing it I would use the 6.15 motor.

 

[woodlandfarms]

SS

Thanks so much for the great answer... Will give that motor the consideration it needs.

Carl

 

[J_J]

Look at page 8 for some tiller rpm's.

http://www.gearmore.com/partsbooks/HTillerBook.pdf

 

[woodlandfarms]

Well. At the end of the day it came to a crashing end. both pieces were not in acceptable shape, and I was an idiot for not asking, but the tiller was one of the korean rescues and parts are scarce.

Going to build my on post hole digger. Wife is on board, budget will be $500 all in with hoses, 12" digger, and motor and mounts.

Finishing the grapple 1st. Wife says I have too many unfinished projects.

 

[J_J]

Someone on the PT forum changed out their hyd wheel motors, and they might make some good auger motors for less money.


Do you remember this post by GRAVY.

http://www.tractorbynet.com/forums/power-trac/91387-better-late-than-never.html

A 12 in auger from PT is about $300.
24 in----------------------------$800