For the brain trust,help I am trying to make a pto post hole digger hydraulic and need to know what motor to use.This will be run on a skid steer with about 2300 psi and 19 gpm.I am going to direct couple to the input shaft of the gear box so I will need 540 max rpm output of the motor.Can anyone tell me brand and number of a motor.Also what is the difference between case drain and no case drain on motors.I have been looking for info for a week and getting more confused by the minute.Thanks for any help you can give me. Neil
- Thread starter HNM
- Start date
retired farmer
Well-known Member
Google Surplus Center and call them. I am sure they will be able to help you. They sell all kinds of motors, pumps and cylinders.
Mike(NEOhio)
Well-known Member
- Location
- Newbury, Ohio
Motors are rated by cubic inches per revolution. 19GPM is 4389 cu.in. per min. 540 RPM requires 8.12 cu.in. per min.
buickanddeere
Well-known Member
You don’t want or need 540rpm on a post hole digger . 150rpm into the gearbox is lots .
Surplus center, item 9-8632-bbb model 255115f3115sssss gets you 539 rpms with 16 GPM. That would let you direct drive the unit. Some use a gear reduction type motor but direct is pretty easy to build. Check Land Pride site and look at the one they sell for skid steers. It is direct drive .
J. Schwiebert
Well-known Member
You also need to remember that neither the pump or the motor is 100% efficient so if your pump is 85% eff. take that amount of flow and take 85% of that to see how much flow you have available at the motor.
ptfarmer
Well-known Member
- Location
- San Antonio, Tx
A pto drive post hole digger has a 3.0:1 gear reduction so 540 rpms is reduced to 180 rpms. I have a Danuser hydraulic digger for my back hoe, here are the hydraulic motors they use http://www.danuser.com/attachments/auger-systems/hydraulic This should be helpful on finding a hydraulic motor.
ptfarmer
Well-known Member
- Location
- San Antonio, Tx
Dang no edit!! my Bobcat skid steer, not backhoe.
fixerupper
Well-known Member
Buick is right. 540 is screaming. I converted my old Danuser to hydraulic drive using a hydraulic motor that drove the reel on an old Deere bean head. The tractor has a 16gpm pump but I highly doubt if the motor gets more than 10gpm. The auger is now on the front of the loader and runs at about half the speed it ran when it was PTO powered but now with the down pressure of the loader I can basically corkscrew the auger into the ground, shut it off and pull it out. I don’t know why I would want it to run faster. Power wise the motor is just adequate but not over powered. If the auger catches a rock it stops the auger before damage is done.
Steve@Advance
Well-known Member
Like others said, it's doing the math to determine volume per revolution to get RPM.
As for the case drain, some motors require a separate drain line back to the hydraulic tank to keep pressure off the output shaft seal.
For your application you would want one that does not need a case drain.
As for the case drain, some motors require a separate drain line back to the hydraulic tank to keep pressure off the output shaft seal.
For your application you would want one that does not need a case drain.
rlp in Co.
Well-known Member
Interesting project. Let us know how it works out.
fixerupper
Well-known Member
I should explain my auger a little more. It’s an 8 inch auger. The motor I use would probably struggle with a 18 or 24 inch.
The original PTO drive probably had a shear bolt for overload protection. The size of that shear pin will give you an idea of how much torque you need to deliver to the gearbox. Can you use the same shear bolt for overload protection or will you need to use a pressure relief valve or a slip clutch?
High torque low speed hydraulic motors are big, heavy and expensive due to their large displacement. It might cost less to add a V-belt or roller chain speed reduction and run a smaller displacement hydraulic motor at a higher speed.
High torque low speed hydraulic motors are big, heavy and expensive due to their large displacement. It might cost less to add a V-belt or roller chain speed reduction and run a smaller displacement hydraulic motor at a higher speed.
ptfarmer
Well-known Member
- Location
- San Antonio, Tx
My skidsteer with 11 gpm, with a 12" auger with the Danuser you control the speed by the rpm's. With a full 11 gpm, and if I hit something that won't move (big rock, bug root) it will stop the hydraulic motor.
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