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Hydraulic Motors

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Carl Wilson 404/09/2013 22:52:41
668 forum posts
53 photos


In the middle of a thought experiment that might lead to my building an hydraulic motor.

Seem to remember a few years back seeing an article in either ME or EiM in which the author described construction of petrol/hydraulic loco. Think bent axis hydraulic motors had been made. Can anyone shed any light on this?



Ady105/09/2013 05:49:58
3463 forum posts
513 photos

Put "petrol hydraulic" into the searchbox


There's a few returns with ME numbers

5"g.petrol-hydraulic by Mr Faulkes

petrol-hydraulic locomotive by C.Faulkes

Mr Smith's petrol hydraulic locomotive

G.T.Harris' 5"g. petrol/hydraulic loco


Ady105/09/2013 06:27:43
3463 forum posts
513 photos

"Oilie", J.Harlow's petrol-hydraulic, issue 3526 page 1171

and Oily is about right

If you do take this route be prepared for a messy system which drips oily pollution everywhere

The only hydraulic systems I've ever come across which didn't spew oil out all over the place are car jacks and fully enclosed automatic transmissions

(I worked with hyd. pumps and cranes at sea. Bottom line is if it needs any pipes then it's going to get messy and smelly)

Edited By Ady1 on 05/09/2013 06:40:07

Hi Speed Scrap05/09/2013 11:12:43
22 forum posts

Hi Carl,

something like this may interest you, google,, and

download brochure.

I made a few tiny ones similiar to these many years ago, they worked

very well. (no connection to this company)


Carl Wilson 405/09/2013 14:02:20
668 forum posts
53 photos


Thanks for all your contributions. I've also worked with hydraulics over many years both in aviation and marine settings.

I'm looking at the feasibility of either trying to produce a gerotor type motor or a radial piston type. The gerotor would probably not be a true gerotor motor but rather an internal gear type motor. Similar to the more familiar external gear pump/motor but with an internal ring gear and smaller planet gear. A crescent shaped lobe seals the intake and outlet areas between the two gears. I'm trying to source some internal gear rings as I think it'll be easier to buy these than to make them. Anyone know of a source?

The radial piston idea could be like a "Staffa" motor. A number of radially mounted fixed pistons would bear against an eccentric on the output shaft. As each piston extends the shaft rotates.

Thanks again for all your help.


chris hallaway09/11/2014 17:50:10
2 forum posts

Hello Carl,

Just noticed your enquiry and thought you may be thinking of Roy Amsbury's articles in Model Engineer some while back. He had a go at a 5 inch gauge Hymek locomotive and started of with a hydrostatic type transmission. This didn't work out in the end despite heroic efforts on Roy's part and he finished up with a mechanical transmission. It's all described in MEs for 17/06/88, 15/07/88, 19/08/88, 16/09/88, 21/10/88 and 18/11/88. Even if inapplicable or too late it's an interesting read.


Brian Wood09/11/2014 18:54:47
1895 forum posts
37 photos

Hello Carl,

I'm rubbish at adding links, they never seem to work for me, but internal ring gears are available from HPC Gears at Chesterfield Derbyshire phone 01246 268080 email

You may not like the price



Edited By Brian Wood on 09/11/2014 18:55:17

Gordon W10/11/2014 10:15:49
2011 forum posts

I don't really understand what you are trying to do, build a motor and pump from scratch? If not there are a lot of small motors out there. Some garden tractors had all hydraulic drive, flail cutters, golf carts etc. May be worth a look.

V8Eng10/11/2014 10:55:41
1274 forum posts
27 photos

I know next to nothing about Hydraulics but for many years motor vehicles have been fitted with compact hydraulics for power steering etc.

Some (I'm told) have battery powered pumps, it might be an idea to check if there are any scrappies in your area to have a friendly chat with.

Edited By V8Eng on 10/11/2014 10:56:22

Carl Wilson 410/11/2014 12:06:43
668 forum posts
53 photos

Thank you for your replies and help gents. As you can see this post is a year old now. It was originally a thought experiment. What I was trying to do was to distract myself and get some respite from the most traumatising and tragic event that has ever happened to me, and which has left me utterly bereft.

No need to worry, I have all the info I need if I ever decide to go anywhere with it.

Thanks again.


Muzzer10/11/2014 18:42:11
2904 forum posts
448 photos

There are quite a few cars nowadays with electrohydraulic power steering (EHPS), such as the BMW Mini and several Fords from memory. However, you won't find any hydrostatic motors in them, only the constant flow pump, control valve and rack (which contains the actuator piston). Even the smallest cars are going to have pretty large motors in them (about 1kW or so). I can't think of a smaller, commonplace application using hydraulics but they must surely exist.

Having worked with all of the major golf cart manufacturers, I can tell you that they all use electric drive (no hydraulics). Aerial work platforms, electric pallet trucks and small fork lifts might be a good place to look.


Mark P.10/11/2014 19:41:04
597 forum posts
6 photos

They have them on airliners known as HMG. hydraulic motor generator powered from the aircrafts main hydraulic system,used if the engine driven generators fail.

Mark P.

Les Jones 110/11/2014 20:09:29
2069 forum posts
141 photos

Citroen cars with hydropneumatic suspension have an electriclly driven hydraulic pump that is used to raise the suspension to give different ride heights and suspension levelling.They normally only run for a short time so they may overheat if run continuously.


Carl Wilson 411/11/2014 04:45:36
668 forum posts
53 photos

If I was going to do it I'd probably use something like a Danfoss OMM series motor. But I'm not so no worries.

Ian S C11/11/2014 10:07:05
7348 forum posts
229 photos

Some ride on mowers use Hydraulic motors for the main drive (either 2 or 4 wheel drive) and one for each cutter, the one I'm thinking of has 3, It is powered by a 3 cylinder Komasu diesel, a lovely little motor, quite quiet.

Some of the machines we built for feeding out bails of hay were powered by a hydraulic motor from the tractor hydraulic system, the motor we used was about 4" dia x 5" long. This system replaced the wheel driven method used on most of our machines. Both systems have plenty of power, with 2 heavy bails on the deck they could weigh nearly 2 tons. Ian S C This is a hydraulic drive machine with an extra long deck to carry 3 bails of hay. Plenty of power in a motor that size for a small loco, and no leaks.test 036 (640x480).jpg

Carl Wilson 413/11/2014 08:37:50
668 forum posts
53 photos


If I was going to do this then I would probably use something as shown in the photographs below. This is also a good example of the type of thing I have to deal with on a regular basis. You are looking at a subsea ROV operated milling machine with hydraulic motor drive to the leadscrews for the XYZ axis and the spindle. This machine is designed for a specific task in the process of removing old spool pieces from a subsea vertical riser. So I'll be doing some milling at 1300 metres. There'll be a plentiful supply of coolant.


This shows an OML series Danfoss motor driving one of the leadscrews. Other pictures show the same motors driving other leadscrews on the unit.



The gearbox and hydraulic drive to the cutter.

Chris Gibson 120/03/2016 16:57:16
1 forum posts

I would like to build a small, radio controlled model (say 20th of full size) of a JCB with backhoe. I am trying to find details/drawings/information of cylinders, pistons and hydraulic pumps at suitable size. Can anybody suggest sources of books or drawings please?

Neil Wyatt20/03/2016 21:22:20
15982 forum posts
674 photos
73 articles

Hello Chris,

Glad you were able to find us!


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