Hydrostatic ATV

[kdlklm]

I've been doing a little research on building my own hydrostatic 4x4 ATV with high and low range. I would like to be able to get between 20-25 mph out of it. It will have articulating steering. I'm looking at an engine between 30-40 hp. I'm looking for advice on what size of pump and motors to run. The nature of the design will require it to have four hydraulic motors, plus the steering. It will be for a wheelchair user, and this is a similar design attached.

Thanks
Keith

 

[BruceWard]

Very cool idea. I think the biggest challenge will be finding suitable tranmissions for each of the motors.

 

[Code54]

Very cool idea

 

[workinprogress]

Sounds like a great project. Below is a good web site with some calculating tools. I would suggest starting with the tire size and going from there. So something like this:

Garden Tractor rear tires or ATV around 23" diameter
So 300 -400 rpms would get you 20-27 mphs. (Using Vehicle speed calculator)

A simple design would be a hydraulic wheel motor. This would result in a 4 wheel drive system (one motor for each wheel). A quick check found a few that max out at 300 rpms but most were more like 150 rpms. So for a rough calculation one of these motor give 150 rpm at 8 gpm.

With 4 motors you will need 32 gpm to get your 150 rpm but this only gives you 10 mphs wiht those 23" diameter wheels. The combinations are endless so I suggest a few minutes with the below link might get you some focus.



Baum Hydraulics Corp :: Spec Calculator

 

[brokenot]

A simple design would be a hydraulic wheel motor. This would result in a 4 wheel drive system (one motor for each wheel).

There's really nothing simple about having four individual wheel motors for a drive system, especially since the OP is looking for some speed out of the vehicle. For example during turns, the outside wheel motors are going to want to push the inside motors. Designing a drive system that isn't going to skid the tires in turns will get pretty complex.

Additionally, hydrostatic drive isn't really the way to go for the kinds of speeds mentioned. You're going to need some serious hp to move the kind of oil it takes to go 20-25 mph....especially with four wheel drive. If you have the horsepower/pumps/motors to obtain those kinds of speeds, then you're also going to need a pretty good sized reservoir or a big cooler to dissipate the heat generated.

While I admire the ambition to tackle this project, I'd hold off on purchasing any bits to get started without having a solid plan in place. First on the agenda should be (trying to) find an existing design to get a better idea of what's going to be required. It will probably be easier said than done though. Hydrostatic drive systems offer several advantages, and are the power transmission method "go-to" choice in many applications.

High ground speed applications are definitely not their forte though. Too much input hp required, too much heat generated, too many losses due to the various component inefficiencies, etc.

Another thing to consider is the control setup. We have some Kubota RTVs at work that are hydrostatic drive. Operators often complain about the on/off nature of the drive system. When you step on the pedal to go....you go. But if you're cruising along at 10 mph or so and let off on the "go" pedal, the braking effect will toss you through the windshield if you're not used to it. You don't coast at all like you would with a regular transmission. And these are factory-built machines that are pretty well sorted....

 

[Iplayfarmer]

Take a look at golf course reel mowers. They have the pumps, the hydraulic motors, the variable flow valves, and everything you'd need. I've picked up a few here and there because of the hydraulic parts they can donate. I have one sitting in the pasture right now with a 35 hp diesel engine. It sounds like the perfect start for whatever project you'd be tackling.

 

[Renze]

make sure you dont overspeed them wheel motors. Lots of hydrostatic wheel loaders die that way, by traveling from jobsite to jobsite. The oil turns hot at high speed, low torque.

 

[kdlklm]

I might have to sacrifice some speed because of the obvious heating issues, and a massive amount of horsepower that it takes. As for steering, the unit above in the photo doesn't use any kind of sophisticated steering system to slow the motor down on the one side, most steering will be done at low speeds anyway. I've still been hunting for something to compare the horsepower to speed and torque ratio, like the mowers suggested.

Braking is a big consideration as well, the comparisons I have are my zero turn lawnmower and my hydrostatic tractor. They both coast when the engines are running and reversing the unit will slow it quickly.

There is the option of going to the electric hybrid type of system, but they tend to lack the low-end torque that I would like to have for pulling stuff. And electric motors can heat up pretty good to.

Keith

 

[J_J]

The Power-Tracs all use VSP , variable speed pumps, and some large hyd wheel motors. The ground speed on our units are about 8 to 12 MPH. A foot control turns the lever on the the VSP swash plate, and controls the speed of the fluid through the wheel motors. Power-Trac also produces a hydro ATV, 6 wheel drive using wheel motors.

You could use use one hyd motor each side and drive the wheels by chain if it is not articulated.

Some of the wheel motors are in a series/parallel configuration.

So in essence, you need to compute the size of the wheel motors in CC, and the torque developed to push your machine at a certain speed, including the weight of all the components, and an avg person of about 200 lbs. . That will dictate the size of the pump, and the size of the pump will dictate the size of the engine HP necessary to power your machine. Keep in mind the 85% efficiency of the pump and 85% on the motors.

Might be best to use a small engine and transmission out of a small car to power the unit. Radiator and fan, etc.


ATV Hunt Vee

http://www.power-trac.com/VideoClips/WindowsMedia/UVclass.wmv

http://www.power-trac.com/uvclass.htm#atv

 

[kdlklm]

Does that ATV use six separate motors for each wheel, and one pump. Or does it have more than one pump. Because the drive system is virtually exactly what I'm looking for. I do like the idea of having articulating steering, because I do a lot of driving in my yard and on my grass, and I think the skid steer would chew up my grass too much. I also have to have a kneeling system for the front, so a wheelchair can be back in, so that kind of eliminates having a front axle.

Keith

 

[J_J]

Yes, each wheel has a hyd motor. Don't know about the pump. It probably has two, but am just guessing. It uses a joystick for steering.

 

[brokenot]

The Power Tracs look interesting, but you can see how speed limitations come into play. In the video, they say ground speeds up to 16 mph can be attained, but in their literature on the website, it says 14 mph is max. You don't see them actually do it in the video either, because with the weight of that machine and only a 25 hp engine under the hood, it won't be able to do that speed unless it's on perfectly flat, solid ground. We have four Toro Dingo mini-skidsteers at work with 25 hp Kohler engines, and they have plenty of torque for pushing, but if they were "geared up" to attain ground speeds of 14+ mph, the drive torque available would be next to nothing. There are just too many losses along the way in the power train.

When gas was up to $4 a gallon a year or two ago, I read quite a few posts on a website owned by a couple of guys that were building hydrostatic motorcycles and smaller commuter-type cars. They touted the "efficiency" of the drive systems, and said that infinitely variable transmissions were the wave of the future. While I wouldn't argue the point about infinitely variable transmissions, I would argue the hydrostatic drive isn't the way to do it. Hydrostats have been around forever, but you simply do not see them used by any manufacturer in an application where high(er) ground speeds are desired.

As for engine selection, upgrading your hp by using a car engine is an easy way to go, lots of the aerial equipment we have uses Ford's 2.3 or 2.5 engine rated at 80 hp or so. When using a car engine though, lots of folks forget about these cheap or free engines not being equipped with a governor of any sort. You might think you can stay on top of the engine rpm as speed and/or load changes by controlling the throttle yourself.....but you'll stay pretty busy trying. Our stuff uses electronic governors which are available for around $500. Another less-expensive option, would be to find a mechanical belt-driven governor from something like an older forklift. Long story short: If you don't have a governor dealing with changes in engine load on something like this, you'll either be constantly killing the engine, or over-revving the engine.....or both.

 

[evo803]

This is not exactly what you are looking for, but this is an articulating,oscillating AWD vehicle for someone in a wheel chair not nearly as fast as you want but will suit many other of your needs.

YouTube - New Style ATV

 

[kdlklm]

This is not exactly what you are looking for, but this is an articulating,oscillating AWD vehicle for someone in a wheel chair not nearly as fast as you want but will suit many other of your needs.

YouTube - New Style ATV

yes that is very much what I'm looking for, and I have seen that before. But it requires the user to transfer into the machine. Which I would like to be able to avoid.

 

[kdlklm]

The Power Tracs look interesting, but you can see how speed limitations come into play. In the video, they say ground speeds up to 16 mph can be attained, but in their literature on the website, it says 14 mph is max. You don't see them actually do it in the video either, because with the weight of that machine and only a 25 hp engine under the hood, it won't be able to do that speed unless it's on perfectly flat, solid ground. We have four Toro Dingo mini-skidsteers at work with 25 hp Kohler engines, and they have plenty of torque for pushing, but if they were "geared up" to attain ground speeds of 14+ mph, the drive torque available would be next to nothing. There are just too many losses along the way in the power train.

When gas was up to $4 a gallon a year or two ago, I read quite a few posts on a website owned by a couple of guys that were building hydrostatic motorcycles and smaller commuter-type cars. They touted the "efficiency" of the drive systems, and said that infinitely variable transmissions were the wave of the future. While I wouldn't argue the point about infinitely variable transmissions, I would argue the hydrostatic drive isn't the way to do it. Hydrostats have been around forever, but you simply do not see them used by any manufacturer in an application where high(er) ground speeds are desired.

As for engine selection, upgrading your hp by using a car engine is an easy way to go, lots of the aerial equipment we have uses Ford's 2.3 or 2.5 engine rated at 80 hp or so. When using a car engine though, lots of folks forget about these cheap or free engines not being equipped with a governor of any sort. You might think you can stay on top of the engine rpm as speed and/or load changes by controlling the throttle yourself.....but you'll stay pretty busy trying. Our stuff uses electronic governors which are available for around $500. Another less-expensive option, would be to find a mechanical belt-driven governor from something like an older forklift. Long story short: If you don't have a governor dealing with changes in engine load on something like this, you'll either be constantly killing the engine, or over-revving the engine.....or both.

I think I've come to the reality that my top end speed will be closer to 15 mph than 25 mph. But 15 mph is pretty quick. I still want quite a bit low-end torque for pulling stuff and maybe even having a three-point hitch on the back.

 

[kdlklm]

Yes, each wheel has a hyd motor. Don't know about the pump. It probably has two, but am just guessing. It uses a joystick for steering.

is there any possible way you would be able to find out what motors they use, just so I can get an idea of what I'm looking at.

 

[Hozen]

Have you given the thought of having electric moters instead of hydraulic moters power the wheels? Hear me out on this. Electric motors supply loads of torque and you could use a much lower HP engine to supply enough amps to keep everything running.

I haven't crunched the numbers, but I've long had an idea to use a small lawnmower engine to turn 4 alternators to supply enough amps to run electric motors. A couple car batteries would be needed as well, of course. You could probably get your 25mph you want and still have the torque without all the heat. Essentially, you'd be making a hybrid ATV of sorts. Electronic "throttle" controls already exist on the market.

An electric golf cart might be a good place to start. Then, add the engine and alternators to continuously replace the power.

 

[kdlklm]

Have you given the thought of having electric moters instead of hydraulic moters power the wheels? Hear me out on this. Electric motors supply loads of torque and you could use a much lower HP engine to supply enough amps to keep everything running.

I haven't crunched the numbers, but I've long had an idea to use a small lawnmower engine to turn 4 alternators to supply enough amps to run electric motors. A couple car batteries would be needed as well, of course. You could probably get your 25mph you want and still have the torque without all the heat. Essentially, you'd be making a hybrid ATV of sorts. Electronic "throttle" controls already exist on the market.

An electric golf cart might be a good place to start. Then, add the engine and alternators to continuously replace the power.

that has been one of my considerations, it was in one of my previous posts. My concern is getting motors that can handle water and mud without having to enclose them too much. Electric motors to heat up a lot when they are put with a great deal of load. They do lack low-end torque without a huge amount of amps. But I haven't ruled the idea out yet.

 

[brokenot]

I think I've come to the reality that my top end speed will be closer to 15 mph than 25 mph. But 15 mph is pretty quick. I still want quite a bit low-end torque for pulling stuff and maybe even having a three-point hitch on the back.

Gotcha.

Keep in mind though that even 15 mph is going to be stretching it. In that Power Trac clip, they made it clear that they had no "attachments" available for it....such as a blade mount/three point/etc. Sounds (to me) like they made all the compromises they could in order for it to attain an "ATV-competitive" top speed, (and 14-16 mph isn't really competitive anyway), and sort of abandoned the notion that it's suitable for real work.

On another forum I frequent, one of the topics frequently discussed are issues with lawn and garden tractors. Breakdowns and lack of reliability are common discussions. The overwhelming majority of "issues" are experienced by the operators that are continuously asking too much of the machines. A good rule of thumb, is to consider what attachments the tractor manufacturer offers for a particular model. Lots of these guys buy a tractor and then build their own trailer, (that's too big), to pull around behind it, or they hook up to a large spike aerator, (and then add a bunch of weight to the tractor for traction), and try to drag it around. They can go right to the manufacturer's website or sales brochure and see that all that's listed for accessories for their model is a light-duty yard cart, and somehow that doesn't register.

In Power Trac's situation, I think the fact that they don't offer attachments is very telling. It certainly "looks like" it could be a real workhorse, but....

 

[evo803]

Search for the Ventrac series 300 they have done something also like you want.