Hydraulic motor and pump help

[Metalburner]

So I'm in the works of building a mini dozer similar to the Struck Corp MD750 and the MT1800/2000, with independent hydraulic wheel motors vs doing a hydrostatic transaxle and putting brakes on each axle. Expected weight is going to be around 800lbs, possibly higher. What this will be used for is pulling a plow for gardening or other ground engagement, as well as having a front loader for moving snow, dirt, gravel, or sand. Would like to use a Honda GX390 or possibly a Briggs 16hp V-twin, depending how much power I'd need.

Where my first problem is, I'm not sure what size hydraulic motor I would need for the drive. I'm either going to use dual #80 roller chain or maybe ca550 chain, if I can get 9-10" diameter sprockets. I would also like to do a gear reduction, in that, from the wheel motor there would be a 10 tooth #40 sprocket to a 35 tooth sprocket on an axle to the track sprockets. I've looked at using zero turn mower wheel motors on surplus center from Hydrogear, but I don't want to go much faster than 2-3 mph; and most of them were rated for 5-10mph, depending on model. So I'm not sure what way to go.

Next part is hydraulic pump size for everything. I'm not sure what size I would need to use the motors and using the front loader at the same time. The front loader will utilize 2" bore and 18" stroke welded cylinders for the arms and a 2" bore 10" stroke cylinder for the curling of the bucket. Frame of the mini dozer and front loader will be made from 2"x4x1/8" tubing, as it'll be more than adequate for the whole thing.

Another reason I wanted to stay away from the zero turn wheel motors is, I'm not sure how long they would last for ground engagement. This isn't some toy, it will be used and I'd like it to last for years. When I looked at the MD750 in the manual, they don't mention the specs of the wheel motors or the size of the hydro pump.

Main inspirations was the model from the mini dozer near complete build on here from a few years ago.

 

[oldnslo]

Looking at the parts used for the MD750 i appears they had a single gear pump feeding everything. Motors looked like the were probably low speed high torque geroter or geroler style but not sure.

Looked like a three section directional valve, feeding a second three section valve. First valve was for drive and second one one for implements. What I am not sure of is if there was some form of flow splitting device in the steering valve that always supplies some flow to the implement valve. If not traveling and using implements could pose a problem.

Simple but effective lower cost system.

Going to a full scale Hydrostatic drive like used in skid loaders is the other end of the cost spectrum. Gives better performance but requires significantly more room for components.

Size of components will depend on several factors.

The engine size selected dictates the pump size and pressure at which it will operate at.

Pump size and gearing will help select the motor size. etc.

Agree that zero turn transaxles probably would not survive ground engagement higher power use.

 

[Metalburner]

I like the idea of full hydraulic drive for the sake of a lot of torque. See from the very little I know, when I look at hydraulic motors, they are rated at max gpm, say about 15.8gpm, would that mean you would need a 30+ gpm pump to run two motors? I know what you are talking about, I believe they call it a priority valve or something like that, where it splits off to run a few things.

At work we have a snowrator that has 4 wheel motors and a 48" plow with 30* of angle adjustment to the left and right, powered by a GX390 engine. If they would give complete specs of the hydro system, I'd have a better idea of what to look for. I hadn't tried adjusting the plow while moving, since the drive controls are like zero turn walk behind levers and it would be very difficult, if not dangerous to try to adjust the plow while on the go. The wheel motors from a zero turn I've looked at on surplus center are rated for equipment weighing over 1200lbs, but like I've said, I don't know if they'll hold up.

We have a driveway that's just under 100' long and about 16' wide all flat, if that helps.

 

[oldnslo]

Metal burner,
Just because a motor is rated for 15 GPM doesn't mean you have to use 15 GPM to operate it. They will turn and develop full torque at 2 0r 3 GPM also. This is the feature that makes HST's nice for loader work. Infinite speed control with basically full torque capability at all speeds.

Zero turn motors: Depends on the style of wheel motor. Eaton check ball style will die an early death under heavy usage. LSHT (Low Speed High Torque) Geroter or Geroler style motors will survive longer under heavy duty use. Weight rating may be based on bearing capacity if these are direct wheel drive motors.

Axial or radial piston will probably provide the longest life under heavy use but they are also the most expensive. Some ZTR trans axles use a axial piston design but they are limited in duty cycle due to heat dissipation capabilities.

I would suggest starting by doing some design calculations based on the information you provided.

Use your track sprocket size to determine what RPM it has to spin at to give desired travel speed. Then use you intended gear reduction to figure out what hydraulic motor RPM is required to provide this travel speed.

Then you have to estimate required drive torque or tractive effort required to pull implements, turn etc.

Using this info size your hydraulic motors.

Hydraulic pump size will be determined by engine HP, and desired operating pressure. Note: General rule of thumb subtract 10% or engine HP for running alternator, cooling fan / flywheel blower, etc.

Example: You could drive a 9 GPM pump @ 2,500 PSI with 15 HP.

 

[Metalburner]

So with a Dynamic low speed high torque motor with a displacement of 9.5 cubic inches, rpm of ,300, gear ratio of 3.5 and track diameter of 12", I'll get 3.05mph and a torque out put of over 9000in/lbs or almost 800ft/lbs.

 

[oldnslo]

Metal,
I didn't check the torque values but I believe the flow required is off. 300 RPM x 9.5 CIR = 2850 cubic inches/min divided by 231 = 12.34 GPM.

NOTE: You will only have half of your total pump flow for driving each track.

Not sure if you know this but for figuring travel speeds with track you use the sprocket diameter not the outside of track. Reason for this that you are laying the track and driving over it.

 

[Metalburner]

Oh okay. I had a feeling that was what I needed to input. So then it would be a 10" sprocket. So going by that I would need a 12gpm pump? This is where I get confused. Sorry if I am causing any issues.

 

[Metalburner]

To help with how I got the 9000in/lbs, I started with 2750 as a baseline, since that particular wheel motor is maxed rated 3200. I figured 2750 would be a good safety margin.

This is the motor I'm thinking on using if it helps. Sorry the link is in mobile, I'm mainly using my phone for posting. http://m.northerntool.com/products/shop~tools~product_200319051_200319051?hotline=false

 

[oldnslo]

Below are some example sizing calculations:

Using the 10" diameter I get 101 RPM drive sprocket speed required for 3 MPH travel speed.

101 x 3.5 gear reduction = 354 hydraulic motor RPM

Based on 15 HP available from engine you would have capabilities of 9 GPM @ 2,500 PSI

ignoring implement hydraulics this would provide 4.5 GPM per drive motor.

At approx 85% efficient a 2.5 CIR motor would provide 354 RPM.

Hydraulic motor torque: 2.5 CIR @ 2,250 PSI differential across the motor equals 74.6 ft-lbs @ 100% efficient. that would be approximately 260 ft-lbs at drive axle. I have no clue if this would be an adequate amount of torque or not.

Drop your speed to 2 MPH and you could use a 3.75 CIR motor which would develop around 110 ft-lbs torque at 2,250 PSI.

Big unknowns: What is the required torque / drawbar pull required for your machine to operate?

System efficiencies: Components vary greatly. A good system is 85 - 90% lesser quality components can drop this to 50%. I would suggest doing your best to find actual documentation on expected performance for the components you are looking at. Some companies provide good documentation and others don't provide much at all.

I would also look into the travel control valves. Not sure if companies valves designed for this but finding valves rated for the flow rate with good metering characteristics will making changing speeds, turns, slow maneuvers much easier.

 

[Metalburner]

I'm almost tempted to buy parts from a ditch witch sk500 or 750, to make this easier.

 

[Metalburner]

So I'm reading a model off of Parker wheel motor and pump set up. It appears to me that each wheel motor requires it's own pump. So if the wheel motor is 10cir, it needs a pump of about .62cir. So in total, unless I wanted to run a line from the pumps to my hydraulic loader, I'd need a third pump dedicated. I know the loader needs about 5.5-6gpm or a .32-.36cir pump.

I can see why zturn mowers use 26hp+, need about 1/2-3/4 dedicated to the hydraulics, then the rest for a mower deck.

I am hoping my math is correct based off of what I'm reading from Parker from their specs
HTJ Medium Duty Integrated Hydrostatic Transmission for vehicles up to 18 lb GVW | Parker NA

I'm not using this combination, just using it as a reference point for how large of pump to motor. The motor setup is way faster than what I'd ever what to go.

 

[MossRoad]

Don't know if this will help you any or not, but my Power Trac is an articulated machine with 4 wheel motors. I have three pumps.

One pump is a variable volume pump. This provided directional control of the wheel motors.

Then there is a second pump that provided 8gpm at 2500psi for the main PTO. This PTO powers implements, like mowers, brush cutters, tillers, etc...

Then there is a third pump. This 3rd pump provides about 4gpm at 2500 psi. It feeds a steering valve. The steering valve drives two steering rams. The steering valve has a power beyond port that provides power to a valve bank that controls the loader up/down, dump/curl and a 3rd function for the quick attach valve, which is also use for power angle of implements like plows and brooms, grapple, etc...

It appears you need independent directional and speed control of two wheel motors, plus power to implements. You're gonna need more than one pump, I'd think, or you're gonna have problems with drive priority when using implements.

Good luck with your project. Sounds fun. :thumbsup:

 

[oldnslo]

So I'm reading a model off of Parker wheel motor and pump set up. It appears to me that each wheel motor requires it's own pump. So if the wheel motor is 10cir, it needs a pump of about .62cir. So in total, unless I wanted to run a line from the pumps to my hydraulic loader, I'd need a third pump dedicated. I know the loader needs about 5.5-6gpm or a .32-.36cir pump.

I can see why zturn mowers use 26hp+, need about 1/2-3/4 dedicated to the hydraulics, then the rest for a mower deck.

I am hoping my math is correct based off of what I'm reading from Parker from their specs
HTJ Medium Duty Integrated Hydrostatic Transmission for vehicles up to 18 lb GVW | Parker NA

I'm not using this combination, just using it as a reference point for how large of pump to motor. The motor setup is way faster than what I'd ever what to go.

A true hydrostatic drive uses variable volume pumps feeding a motor in a closed loop environment. The variable volume pump allows adjustment of travel speed to match HP available. Skid steers typically have two variable pumps and either two or four drive motors. They also have a 3rd pump for implements.

The Struck unit used a fixed displacement gear pump so it has to be sized based on available HP to drive it. Two totally different designs doing similar jobs. Each of the variable pumps probably probably cost about 3 times as much as the gear pump which is why they are used for "hobby" type equipment but less frequently used for serious use equipment.

 

[Metalburner]

So am I better off spending the money for two variable pumps plus a third gear pump?

 

[Metalburner]

Don't know if this will help you any or not, but my Power Trac is an articulated machine with 4 wheel motors. I have three pumps.

One pump is a variable volume pump. This provided directional control of the wheel motors.

Then there is a second pump that provided 8gpm at 2500psi for the main PTO. This PTO powers implements, like mowers, brush cutters, tillers, etc...

Then there is a third pump. This 3rd pump provides about 4gpm at 2500 psi. It feeds a steering valve. The steering valve drives two steering rams. The steering valve has a power beyond port that provides power to a valve bank that controls the loader up/down, dump/curl and a 3rd function for the quick attach valve, which is also use for power angle of implements like plows and brooms, grapple, etc...

It appears you need independent directional and speed control of two wheel motors, plus power to implements. You're gonna need more than one pump, I'd think, or you're gonna have problems with drive priority when using implements.

Good luck with your project. Sounds fun.

Exactly. At first I wanted to use one large pump to power everything, but the more I look into it, the harder it would be to implement that into it. Cause then I'd need one large pump and a large engine to run it. Even on a mini skidsteer like a Ditch Witch SK750, they have 2 pumps, one for the wheel motors and another for the loader arm and implement(s).

I'd have no problem running 3 pumps if it came down to it, because I can design the mini dozer around it. I'm not planning on using it to build a house foundation...maybe to do a shed foundation, but that wouldn't be any larger than a 20'x30' or there abouts. Trying to build it like a glorified garden tractor.

 

[MossRoad]

It would seem that if you used two drive pumps and two drive motors, you'd have lots of trouble syncing them to go in a straight line. They'll never turn at the same speed ever. You'd be constantly on the controls. Sounds awful. :laughing:

So how does a crawler work if you use only one drive pump to drive two hydraulic motors? Again, I think you'd have sync issues between right and left. It would seem like the path of least resistance would be fluid going around a valve when its not open (in neutral). If you opened either directional valve, there'd still be a path of least resistance around the other valve and you'd build no pressure to turn a motor.

Don't crawlers use one pump, driving one motor, driving one differential, and they use brakes to slow or stop a track? It would seem that would be the simplest. One variable volume pump that drives one motor that turns one differential. You'd have a forward and reverse pedals (or a lever) and a left and right brake.

I don't know. I'm just talking out loud. Time for me to go read how tracked vehicles propel themselves.

 

[Metalburner]

I was looking into using a hydrostatic transaxle and putting 10" disc brakes on the axles to turn, rather independent control, the Struck MT1800/2000 did this with a Peerless 2338...however that has been long discontinued. All of our zturn mowers and our Ditch Witch has two wheel motors and two variable displacement pumps. I like the idea of independent control of the tracks to make right turns in the same spot, especially in tight areas.

Trying to find a suitable transaxle to do this is not easy. I'd have to find an older garden tractor like a John Deere 318 and pull that out.

I wouldn't think synching up two pumps and motors wouldn't be that hard. I'd mount the pumps side by side with the same size pulley (unless they came with one) and run a V-belt to the engine to them. This is how all zturn mowers are setup I believe.

Another way I could do it, is how Struck has been doing it with their smaller crawlers (RS1000, RS196k, MD series) is an intricate series of pulleys and belts to a drive chain to the track sprockets. They claim with all the gear reduction on the RS1000 that at the tracks it has 1500ft/lbs of torque. It's pretty complicated to do that in my mind, than it would be to run wheel motors and pumps.

 

[oldnslo]

two variable pumps and two motors is exactly what a majority of skid steers have. The operator running the levers controls direction and speed by changing the variable pump displacement. Same principle as what most zero turn mowers have. Best maneuverability and performance and probably most money

Single fixed or variable pump driving a motor driving a differential with brakes to steer is also common. My guess would second best on performance and ease of operation.

Two fixed pumps trying to drive two motors could prove a challenge since feathering them would require a very good metering control valve and creates heat

One fixed pump feeding two track drive motors. On similar footing would probably track reasonably well turning or varying the speed or driving at less than full speed again requires a good control valve and creates heat.

fixed pump potentially more difficult to control and change direction depending on quality of the control valves. least cost of all.

Metal burner,
It comes down to your fabricating capabilities, what do you want this machine to do and at what cost. Several different options that provide different levels of performance and cost.

With My abilities I would be to buy a used piece of equipment that meets my needs.

 

[Metalburner]

two variable pumps and two motors is exactly what a majority of skid steers have. The operator running the levers controls direction and speed by changing the variable pump displacement. Same principle as what most zero turn mowers have. Best maneuverability and performance and probably most money

Single fixed or variable pump driving a motor driving a differential with brakes to steer is also common. My guess would second best on performance and ease of operation.

Two fixed pumps trying to drive two motors could prove a challenge since feathering them would require a very good metering control valve and creates heat

One fixed pump feeding two track drive motors. On similar footing would probably track reasonably well turning or varying the speed or driving at less than full speed again requires a good control valve and creates heat.

fixed pump potentially more difficult to control and change direction depending on quality of the control valves. least cost of all.

Metal burner,
It comes down to your fabricating capabilities, what do you want this machine to do and at what cost. Several different options that provide different levels of performance and cost.

With My abilities I would be to buy a used piece of equipment that meets my needs.

If I could buy a used machine I would, however most want a lot more than what I'm willing to pay. My fabrication skills are good. I don't have much machining skills nor much for tooling to do that. Any parts I can't make, I'd ever find a machine shop nearby and pay for a part, or buy what I need in store or online.

Most of my fab skills is welding (went to college for it), so I have no issues there. My goals for this machine is to be able to pull a plow for gardening, tow a smallish trailer with wood or rock, dirt or whatever, move a 1000-1500lb fiberglass bass boat around in the yard when need be, and has the ability to move snow in the winter. I had thought about a simple hydraulic blade for snow removal, however a front loader would be a lot more useful.

Like I've stated before, think of it as a garden tractor with a front loader and a cat 0 3pt hitch. It'll be maybe slightly longer and wider than a JD X series garden tractors, but not by much. I figured if I buy parts over time, I can spread out the cost a lot easier than dropping several thousand dollars in one sitting. Excluding the cost of a brand new engine and steel, budget for the hydraulics is $3500, that's brand new or slightly used.

 

[MossRoad]

two variable pumps and two motors is exactly what a majority of skid steers have. ...

Thanks, I did not know that. So I googled "skid steer drive circuit" and go this. Nice.



From here:
http://www.colemanequip.com/CASE/Im...TO-VARIABLE-DISPLACEMENT-PUMPS-0dKb-large.gif