cost of production

[azz7772]

mudN, I have made the calculations and the hydro option has serious displacement to gear ratio problems especially if your are looking for a machine under 900 lbs and limiting the HP to 25 hp. It works out different when if you look at a 1500 lb machine and 40 hp. Simply stated the calculated torque for your wheel motors is not the available pump pressure but 1/3 or 1/4 the pressure as you drive the motors in series. so actual motor differential pressure of 1000 psi on 3000 psi pump for a 6 wheel drive machine. What you end up on the pump side is to oversize the pump displacement to give you the ground speed. But wait, at the higher ground speed we have to decrease the pressure or we overload and slow the prime mover. Once we have selected this high volume pump and matched it to our25 hp engine we cant start it as the starter now has to also spin the charge pump and (2)feathered main pumps along with the engine. Not Ok but we can add a clutch or belt drive for the pump (been done) an on, and on and on. So for 25 hp and 800 lb machine that can climb a 45 deg incline the top speed is 10 mph.

that is a good argument.......... to consider my design I thought of having just one drive motor on each side driving a sprocket/track over free wheeling balloon tires picture a bombardier bombi but with a different track that incorporates the balloon tires. You would have a strong but simplified frame, two drive motors, two hydro pumps in tandem and choice of motor the wheel axles would just have to mount on the outside of the tub bolted through to the frame. t but there would be no bearings in the tub for water to penetrate.you can see in the pic where the sprocket is located that would be what I was thinking.

[jerseybigfoot]

mudN, I have made the calculations and the hydro option has serious displacement to gear ratio problems especially if your are looking for a machine under 900 lbs and limiting the HP to 25 hp. It works out different when if you look at a 1500 lb machine and 40 hp. Simply stated the calculated torque for your wheel motors is not the available pump pressure but 1/3 or 1/4 the pressure as you drive the motors in series. so actual motor differential pressure of 1000 psi on 3000 psi pump for a 6 wheel drive machine. What you end up on the pump side is to oversize the pump displacement to give you the ground speed. But wait, at the higher ground speed we have to decrease the pressure or we overload and slow the prime mover. Once we have selected this high volume pump and matched it to our25 hp engine we cant start it as the starter now has to also spin the charge pump and (2)feathered main pumps along with the engine. Not Ok but we can add a clutch or belt drive for the pump (been done) an on, and on and on. So for 25 hp and 800 lb machine that can climb a 45 deg incline the top speed is 10 mph.

[Beeman]

I was under the impression that chain was pretty good at energy transfer. (http://www.gates.com/facts/documents/Gf000202.pdf).

[azz7772]

I have only owned a hydro drive but watching the vids with everyone having to stop, wiggle and fiddle their machine into reverse then stop and do it again to go forward. Having a hydro drive is so much easier and time saving in the bush trails if the trail is tight, zero turn is a luxury. Also having a bit of time on driving a hydro and just comparing from watching all the vids having instant reverse, and counter rotation is a big plus in the hills up and down.

[mudNmallards]

MudN.. my comparison is with hydrostatic drive and a practical approach for "cost of production". On its best day hydrostatic drive is 75% efficient. There is a weight penalty and there is a cost penalty. Current production gerotor and geroller wheel motors have a poor speed range and efficiency. Torque sensitive controls for hydrostatic drives are expensive and are are usually compensated with excessive hp. is there really a need for instant reverse and instant counter rotation. T-20's are capable of counter rotation.

Bearing in mind that I have yet to spec out anything or even done preliminary calculations and run them through hydrocalc and mathCAD, made a P&ID to look at the system- much less conducted a bench test ( and having a few brews at the room, LOL) so I’m talking off the hoof. These are nothing more than un analyzed opinions at this point- when I run the actual numbers after we come up with the specifications I need to plan against I might be totally wrong and have to go to Rev1.

Actually operating efficiencies of the high end units hits closer to around 90%. (even the bent axis units)- even at 75% that exceeds the efficiency of the internal combustion engine coupled with all the power train losses so I still see it as the most power to the wheel available compared to conventional current designs.

These units ( lot of variation depending on what the final size is) averages in the 25-30 lb weight so for an 8 wheeler that’s a high end addition of about 240lbs. Lets double that to factor in the pump and rest of the system so we are about 500lbs. When you put that on a scale and weigh it against the removal of chains, sprockets, the transmission, associated shaft length no longer needed, clutch assembly and a few other odds and ends I’m guessing you will get about 300lbs of that back so we are only talking a 200lb increase in overall weight and that’s well within the vehicle capacity especially spread out over 8 wheels. Even if I’m off by 50% and its 300, that’s still rather insignificant when its spread over the mass of the unit equally.

Cost- My price range (depending on what final model is spec’d out) will be on the high end around $500. That’s $4000 for 8 wheels. I’ll double that for the rest of the system and a buffer so I’m at about $8000. When all the “stuff” this system is replacing is removed I’ll be conservative and say I’ll get about $3000 back so I’m at $5k. When I do a ROM estimate of the savings in replacing wear out parts, maintenance costs on the replaced systems over the life of the vehicle plus the value add with the availability of optional accessories I think I’m on the good side.

The motors I am considering have an RPM range around 350 on the top end. With a 25” tire @200 RPM is about 30 mph so I don’t see the RPM as a big issue as far as road speed is concerned and if it were to become one a belt/pulley can be installed to increase it. I don’t think I personally would want an AATV driven past 40mph personally but I’m sure there are people who would.

On the torque controls- if we were designing a conveyor at a lumber mill that would carry super heavy loads or massive shocks from stuff dropping on it in a process environment, I would agree torque controls would be mandatory. Given the relative light weight of these vehicles and the fact that tires are going to slip some, my current thought is that a garden variety pressurized accumulator would be more than adequate. That could easily change depending on what the numbers show when I have specifications to run them against.

Instant reverse/counter rotation- Neither of those qualities ever factored into my thought process in the first place (truth is, until I came here and read about them, I didn’t even know they existed in these machines- I go back to my days as a tanker, I can count the number of times I had to neutral steer in my own circle on one hand with fingers remaining and none of them were ever in the field. I also see zero value or real world application for an instant reverse except in the most extreme emergency and those are rare) But since both of them are by products of this type of system I’ll take them.

My reason for starting off with a hydrostatic system simply had to do with modular design, overall efficiency, system reliability, simplicity, reduction of high wear parts, ability to add accessories and a few other benefits. Reverse and rotation never even entered my mind.

There are drawbacks with every system just like there are benefits. If I go this route then I have to remove the heat the system is going to generate. Obviously to get the benefit the pump will have to be turned at a constant speed so that’s going to have to have some noise reduction and a few others that escape my mind at the moment.

[mudbug3]

Yes, a T-20 is capable of counter rotation ,but not in thick mud or you'll smoke your belt. Been there done that. It was'nt until I bought a Mud-Ox that had hydraulic wheel motors, was I able to counter rotate in thick mud and not smoke a belt. The flip side of the coin , is that you won,t be able to get the weight of a hydraulic amphib around 1,200 pounds. The heavier an amphib is the less capable it is when driving through soft mud. With the heavier frame needed to run hydraulics , you then need to run tracks in soft mud to lower your psi on the ground or you'll get stuck. Been there and done that too.

[jerseybigfoot]

MudN.. my comparison is with hydrostatic drive and a practical approach for "cost of production". On its best day hydrostatic drive is 75% efficient. There is a weight penalty and there is a cost penalty. Current production gerotor and geroller wheel motors have a poor speed range and efficiency. Torque sensitive controls for hydrostatic drives are expensive and are are usually compensated with excessive hp. is there really a need for instant reverse and instant counter rotation. T-20's are capable of counter rotation.

[azz7772]

A few years ago RI offered a Trac Max (I think that's what they called it). The rear two axles were the only axles that were driven by the T-20. The front and middle pairs were free-floating. I don't think that model was offered more than 2 years but I'm sure the "Max Guys" would no for sure. I suspect if the model was popular, it would have been offered longer than it was.

As far as tanks go, I'm not aware of any tank or APC that has the drive sprocket in contact with the ground. It's always well above the floating or suspended wheels and as far as I know, cannot be a part of the suspension.

I don't think you could use a torsion bar suspension and still deliver power to the suspended wheels. I think Walter Christie did develop a tank in the 1930's that was able to run without tracks but I'm pretty sure that power was distributed to only one pair of the road wheels and was never run without tracks off-road. I would imagine that trying to incorporate that technology into anything now would be rather expensive. Torsion bars would still require having holes in the tub to accommodate them. Tracks will also add a few bucks to the cost.

For the record, tanks rock!

the drive sprocket would not be down low in the mud it would be up high like a tank. And some mud would actually help lube the sprockets rather than hinder them. we are talking a possibility of a new design. having it driven with hydro motors ,it would counter rotate and, instant reverse. I think it could be made lighter as well to compensate for track weight so it would sit higher in the water to make the tracks swim better. Another benefit would be infinite engine possibilities to drive the pumps and the ability to make a very balanced machine.

[George]

A few years ago RI offered a Trac Max (I think that's what they called it). The rear two axles were the only axles that were driven by the T-20. The front and middle pairs were free-floating. I don't think that model was offered more than 2 years but I'm sure the "Max Guys" would know for sure. I suspect if the model was popular, it would have been offered longer than it was.

As far as tanks go, I'm not aware of any tank or APC that has the drive sprocket in contact with the ground. It's always well above the floating or suspended wheels and as far as I know, cannot be a part of the suspension.

I don't think you could use a torsion bar suspension and still deliver power to the suspended wheels. I think Walter Christie did develop a tank in the 1930's that was able to run without tracks but I'm pretty sure that power was distributed to only one pair of the road wheels and was never run without tracks off-road. I would imagine that trying to incorporate that technology into anything now would be rather expensive. Torsion bars would still require having holes in the tub to accommodate them. Tracks will also add a few bucks to the cost.

For the record, tanks rock!

[mudbug3]

mudNmallards

This is an example of tracks that swim and slide side to side 50% easier than tires do. They are made out UHMW material.

[mudNmallards]

I think this would be a good way to go sprockets are available, seems everyone wants tracks most everyone anyway. Simple hydraulic system just have to design the track so it incorporates the sprocket and can swim descent.

Well, theres no question it will work- it already does.

Tracks V. wheels will be an infinite discussion because they both do things the other wont along with maintenance, stress and load considerations. That’s really application specific as to which is the best choice.

On swimming- I have not even looked into this yet and my only experience with track swimming is with M-113s doing river fording. The big problem I see with tracks or wheels as the sole method of propulsion is that the forward force is negated by the rearward force on the other end. I might think of something else when this aspect is investigated but right now I think any waterborne propulsion is best suited by a propeller or 2.

[azz7772]

I think this would be a good way to go sprockets are available, seems everyone wants tracks most everyone anyway. Simple hydraulic system just have to design the track so it incorporates the sprocket and can swim descent.

[mudNmallards]

what do you all think about two drive motors either up front or out back running a sprocket setup up high on the tub either front or back which would run a track kinda like a snow cat and have all the wheels as free wheeling. The wheels would be for floatation but the drive motors and sprockets would do all the work.it might be feasable to design some kind of suspension this way as well. That would allow more room in the tub as well. Also the wheel axles don't necessarily have to go through the tub which would eliminate water leaking through the bearings.

If I’m understanding you correctly- you just described the modern tank. ( Brings back memories from when I was a tanker- ARMOR is the combat arm of decision and if anybody doesn’t believe that, get on the business end of my gun tube)
It will absolutely work with tracks and you can choose from a chessie (slack track) or torsion bar (stiff track) suspension. They both have been proven from the Russian front to the sunny sands of Afghanistan.

[mudNmallards]

Very interesting facts thanks for taking the time to educate,on some sleds a upgrade kit to a cogged belt is in use and works well,the issues I would see with the present AATV,s construction would be frame flex,debris,and bearing failure causing belt derailment and destroy the belt,whereas chain can take alot more "issues" as it were,how would you address that in a cost effective manner.NCT

Sure, I’ll help you any way I can. I “think” I can solve most of the bearing failures I see here with one post. (I say “think” because when I see bearing pics here or try to look OEM numbers they are not always the manufacturers number so I cannot directly look up the bearing to see what the guts are made of and you cant tell much from the picture of the outside. From the few I have been able to look up that have manufacturers data I believe I see the problem clearly. If what little I have found and looked up is uniform across these machines I can almost promise you that bearing failures will be reduced by orders of magnitude)

Frame stress- I deal with this doing vibration analysis and ping testing all the time. Frame flex is one of my worst enemies in vibration and a machine holding a running alignment under load. My cure has always been beefing up the frame by gauge and/or welding gussets at all stress points. That’s a 1 shot fix. If there is an alternate method I have never seen or heard of it and if someone knows of one I’ll pay money for it because every time I tell a client they need to replace the OEM frame with a stronger one to reduce vibration and hold alignment they give me that “devil stare” and want to know why the OEM frame is inadequate. The answer is that the OEM doesn’t care because they test their stuff on a static bench and are quick to tell you that field applications are your problem, not theirs.

Debris- This is one area the chain reigns supreme. Chains will allow fall through and rarely accumulate crud and a belt can be a crud magnet. Chains are also strong enough to bite through a lot of things- belts just like to shred to pieces. (I guess belts don’t like to crush things much tougher than a finger like chains do) The only 2 cures I know for that are to move the belt drive into a protected area away from exposure to the debris or fully guard them.

Bearings- That’s one of the first things I look at and one of the biggest things I have been researching here. The problem I run into is that an OEM number like # 1234 or the size (6205) doesn’t give me all the information I need to get all the properties of the bearing. If I could get the manufacturer full data I could almost be absolutely certain of what I’m about to say so please allow a little bit of leeway because I’m admitting up front my information on the bearings these machines appear to use by and large is incomplete so this is more a SWAG based on visual observation at this point that would change drastically with different information.

First ( hope I’m not violating a board rule by putting in a recommendation because I’m closely associated with SKF) I would advise everybody on this board who works with bearings in any capacity to go to SKF and sign up. Go to their download technical section and download their white papers. These papers cost from about $3 to maybe $10 (some are free) but you will learn everything short of forensic analysis there is to know about bearings, factoring loads, vibration data, proper lubrication, applications and failure analysis. It will pay for itself by orders of magnitude.

To avoid one of my thesis level posts, we are talking specifically on belts because they have some unique requirements and it does change a little in other applications but its very minor. I’m also assuming the proper strength frame and the axles are robust enough to accept the belt without deflection and all other variables are equal. I’m also excluding alignment which is equally critical but beyond the scope of discussing bearings in relation to lateral load. This is also all in layman’s English, truncating it and not going into all the technobabble so there is not a perfect accuracy sacrificed deliberately for conversational purposes.

To get the maximum benefit from a cogged drive belt it must have proper tension. Tension for these applications is as tight as you can get it plus another turn. This makes the belt bite and hold the pulley over the entire surface area and gives maximum energy transfer. (see it adheres not just to the cog [ lateral force] but grabs at the root of the cog[ which bites the top of the spline of the pulley]) Failure to achieve and hold proper tension puts shear forces on the cog, wears it and eventually rips it off. (and enlarges the gaps in the pulley so now you are tearing up the next belt by default) This is what gives it the superiority when it comes to energy transfer so if you do not have proper tension you lose 50% of the benefit right off the bat and are destroying the belt.

The big problem I see is the bearing. There are 2 types of anti friction bearings. Balls and rollers.

Balls are for high RPM and little load stress and rollers are for low RPM and high stress. (in simple terms)

See, theres a REASON every manufacturer on earth uses roller bearings in vehicle and high load environments. ( be they the “timken” tapered or flat roller) and it applies to these vehicles to because they are subject to the same stresses.

ALL axles regardless of application are subject to radial and axial stress loads

The first big difference is distributing the load over a surface area. Rollers are designed for this because the surface of a roller times the number of rollers comes real close to total load support over the bearing area at all points. A ball is just on the edge and the rest compresses like a rubber ball.

Try this experiment- get some marbles and round pencils on a table. Put a book on top of them and roll it around and peek at whats making contact. You will see it immediately.

That load (combined with shock in the X and Y axes) starts brinelling (flat spotting) the bearing and its just a matter of time at that point and no amount of grease will overcome an uneven surface beating itself or grinding itself to death.

No ball bearing made on earth is designed to accept both stress vectors at the same time. All of them are balls running in a trough. That’s top down stress only. The only 2 exceptions to that are angular contacts and double row sphericals but those are special application bearings.

Now, you put the tension load that a proper belt application requires on a ball bearing (constant radial load) combined with the loads from the vehicle proper- I seriously doubt any ball bearing made would survive any great length of time. They simply are not made to accept that kind of load. Its not a defect in or the fault of the bearing, it’s the application.
This is like the 1 second version on bearings compared to the feature length film and tons of critical information is left out but for those load stresses axle applications have, its best to pull every ball bearing out and replace it with the proper roller and go from there.

Hope this helps you.

[azz7772]

what do you all think about two drive motors either up front or out back running a sprocket setup up high on the tub either front or back which would run a track kinda like a snow cat and have all the wheels as free wheeling. The wheels would be for floatation but the drive motors and sprockets would do all the work.it might be feasable to design some kind of suspension this way as well. That would allow more room in the tub as well. Also the wheel axles don't necessarily have to go through the tub which would eliminate water leaking through the bearings.