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Design Possibility, can or CANT be doneà
2

Design Possibility, can or CANT be doneà

Design Possibility, can or CANT be doneà

(OP)
I’m kicking around an idea and want to get some comments as to its possibilities and maybe even its practicality.

Ok, I spent the weekend watching rock climbers, no not people climbing mountains but modified trucks, Jeeps and moon buggies (Purpose built 4x4’s).  I seen more broken parts (drive line of course) then I see in my 15 years of being a mechanic (12 years ago).  The other observation was the current mechanical drive line creates more limitations then I could count.  This includes traction, clearance, power and the list goes on and on.  Ok, Ok… Here’s my question.

It seems like the power of fluid could solve so many of these problems I have to investigate.  Is it possible with the current technologies in fluid power (Motors, Pumps, Valves and Controls) to build the ultimate 4x4 or even rock crawler using 100% fluid power?  Now I said “Possible”, let’s assume for the monument that money is no object (wouldn’t that be nice).  Could one take say a Ford truck and replace the axels with Hydraulic motors (all 4 wheels), replace the transmission with a pump and the steering wheel with say joy sticks.  Now I KNOW it’s much more complicated than that but for the monument think simple, what do you experts think is this something that could be done?  

I’m not looking for any designs or direction at this point, just your thoughts!!

RE: Design Possibility, can or CANT be doneà

DDame...The simple answer to all of your questions is ABSOLUTELY YES.

Putting aside, for one moment, the inefficiency and the costs ETC...there is nothing that beats the power to weight ratio of hydraulics. It is possible to drive any piece of machinery with hydraulic actuators.

With the control technology available in modern valves it is possible to have infinite control, hydraulically or electronically.

This is a totally unbiased opinion of a Hydraulic Systems Engineer. Ask an Electrical Engineer and see if they agree.

Hydromech...  

RE: Design Possibility, can or CANT be doneà

I agree. Totally possible, high mounted motors at each wheel, no differential pumpkin hanging down, etc.
using hydrsostaic drive, you would also have dynamic braking

controls are the difficulty. Simiply teeing all together would be like an open differential-one wheel unloaded, all the oil goes there and spins 4x normal speed. and no traction.

We are currently working on a 4 axle drive vehicle that is expected to unload one axle at a time as the axles cross bad joints. Similar to driving 4 separate wheels of your truck. Nothing secret about the drive, its copied from previous industry technology.    We will use 4 pumps, 4 motors, (1 pump drives one motor drives one axle. All four are separate from each other.) This of course gives no load sharing at all, if one pump/motor/wheel is fractionally more or less efficient, that drive pressure goes to 5000 and the others go into dragging at 5000 psi. In this case, there will be F & R pressure transducers on each PM package, and speed sensors in each motor.  Overall software and controls will provide displacement (speed) control, the next inner loop limits by pressure to provide load sharing between the four drives, and the final inner loop is wheelslip limiting, i.e. don't exceed a couple percent slip no matter how unbalanced the pressure is.

HST are typically very stiff drives: touch of displcement and pressure spikes up to maximum.  Several companies have 'automotive controls' that approximate a torque convertor drive: slushy with light throttle theen gradually increasing power and response with pedal motion. This allows maximum control and is used for maneuvering applications. perfectly suited for fine traction control.

k

RE: Design Possibility, can or CANT be doneà

Check out a company called Mammoet at www.mammoet.com.  They provide self-propelled modular flat-bed transporters that can interconnect as required to provide about 25 rows of hydraulically controlled wheels.  Each set of wheels turn and drive with a crane-type controller.  These are not climbing trucks but transport trucks for moving 7500 ton offshore platform decks, etc.

John

RE: Design Possibility, can or CANT be doneà

I am biased towards the sprayers.  I design high clearance row crop sprays with hydrostatic drives(www.hagie.com).  We use two pumps with four motors(1 pump to 2 motors). Traction can be improved by linking the motors in a X design.  For example, one pump drives the front left and rear right motors.

With the correct pump, motor and torque hub ratio, I'm sure you could climb over anything.

Nick

RE: Design Possibility, can or CANT be doneà

Another possability is traction motors:

http://www.e-traction.com/TheWheel.htm

I think there are a few other companies that make these sort of "wheel-motors" but i cant find them offhand

RE: Design Possibility, can or CANT be doneà

There is a company called Ifield Motor out of England.  They make an extremely efficient hydraulic motor.  A system was developed with Ford Motor using those motors and accumulators to make a very efficient system for an SUV.  The accelerator was actually controlling the computer which then directed the accumulator to supply fluid to the motor.  It was very smooth and had excellent acceleration.  The idea was put on the shelf and the engineer who helped develop the system went back to England, discouraged.  

Dan Helgerson CFPS, AFPI, AJPP
www.cfpsos.com

RE: Design Possibility, can or CANT be doneà

Theres a surprize - they spent millions reinventing the wheel at probably 10x the price to keep from spending a nickel a unit on royalties

RE: Design Possibility, can or CANT be doneà

Efficiency is another issue to consider.  Many of the lower cost low speed, high torque motors are quite inefficient.  Finding a motor that is efficient at the low end and still within an acceptable price range is challenging.

Dan Helgerson CFPS, AFPI, AJPP
www.cfpsos.com

RE: Design Possibility, can or CANT be doneà

I keep seeing hints of some very practical applications.  The military is looking at this technology for the same reason as your requirements.  

http://www.wavecrestlabs.com/index.html

RE: Design Possibility, can or CANT be doneà

True. The etraction system is on city busses and is doing quite well on the overall system.  

Other info that i have been reading is saying that the gear trains and such max out at 50% eff.  I think i was reading one of these as companies as saying that running one as a motor driving a second as a generator they were getting 80% system eff.

RE: Design Possibility, can or CANT be doneà

I spent 7 years as a hydraulics/diesel tech working on oil exploration equipment around the world.  We used specially made vehicles with hydrostatic drives in the Middle East to the Sahara to the Alaskan Arctic (on land and ice).  In all applications the hydraulic drives were the only solution at the time.  

I finished my BSME after the oil slump in the 80's and have been designing hydraulic systems since.  Hydrostatic drive systems are gaining more popularity with off road equipment as well as in fan drive systems and high tech transmissions (hydrostatic and powershift combined).  I think a hydrostatic transmission system installed on any off road vehicle has advantages over conventional systems.  

The best system I ever used was a powershift transmission driven by a hydrostatic motor.  I crawled over some of the steepest sand dunes and rock structures ever imaginable and was able to maintain good traction.

RE: Design Possibility, can or CANT be doneà

the kind of drive system you are asking about is already in use around the globe, used in open cast mines, here in Borneo for instance there are many trucks, and other ore handling vehicles, manufactured by Volvo/Michigan/Euclid (VME), Leibheirr, and Hitachi.
Your biggest problem is down to size, wheel motors like the Hagglunds Dennison viking range are quite huge, but then you could go onto the Vickers motors, or Staffa, or go as far as the german manufacturers, Brueninghaus, Rexroth, and Beauringers.
If you have any links with deep shaft mines, you could pick up some ideas from drawings supplied with Dosco machinery, or Mindev, BJD, Fletcher Sutcliffe and Wilde,
But basicaly speaking, the idea you had originaly, will work, can work and has already been proven to work, now, when it comes to areas like rock climbing or rough terain, then you have to think about putting your wheel motors on floating floating anchors, and these would have to be actuated by hydraulic cylinders that would be fed by a pressure sensitive control, thus allowing movement in both up and down to compensate the weight displacement of the vehicle, in short and elaborate shock absorber.
in truth, if you ever get a unit built, i would love t see it

RE: Design Possibility, can or CANT be doneà

Just remember that if your vehicle is also going on the main roads at high speed you will want to minimize the sprung mass of the wheel assembly itself to ensure acceptable dynamics over uneven surfaces at speed. Hence a hydraulic wheel motor may not be suitable unless you use a CV joint type drive. Most wheel motor applications are low speed heavy vehicles.

RE: Design Possibility, can or CANT be doneà

That kind of drive has a limited span of gear ratio. Optimize it for rock crawling and you will have about zero effiency at highway speed.

RE: Design Possibility, can or CANT be doneà

I have the solution to which this is to be done.  I have designed a buggy with hydraulics for its source of power.  It runs on 49 inch tires, utilizes "Mud Hog" wheel motors, that are primarily used in rear wheel assist on combines in the ag industry.  Utilizing pumps from Eaton/Vickers (the company which I work) If possible I will try to use aircraft pumps to keep the weight in the center of the vehicle down.  I would eventually like to drive this with a turboshaft turbine engine, and utilize pressurized bladders for fuel and hydraulic storage, This will greatly reduce starvation and help with cavitation to the pumps when on steep inclines.  I was planning on running three pumps, two for the drive wheels, going through flow splitters, and directional control after that via directional control valves. This would allow me to run either the front set of wheels or a side of wheels off one pump.  Full hydraulic steering and suspension controlls.  The steering would have enough degree of freedom to allow all four wheels to steer independantly, allowing both front and rear wheels to tow, and spin 360 deg without any forward travel.  The suspension is a cantilever design with an adjustible upper shock/spring combination via hydraulic actuators.  I have the planns, I just need to purchase the hydraulic equipment.  
I design and test aircraft hydraulic systems for a living.  
I would love to share these ideas with anyone.  

RE: Design Possibility, can or CANT be doneà

tad1299...

The only obvious issue I can see is using a flow divider to drive the wheels.

Going in a straight line...great, turning corners...that may be a problem.

When turning, the inside wheel will want to turn at a different speed to the outside one. Because its moving around a smaller arc it will want to go slower. The flow divider will keep both wheels turning at the same speed.

The handling of the buggy could be scary. But then again...that may be just what you are looking for???

Also, if the buggy has one drive wheel off the ground the flow divider will intensify the load in the motor that is still driving the buggy. That again may not be a problem for you, but it could potentially force the wheel of the buggy.

I wish I could tell you the best way to do it, but I have little experience with drive systems like this...sorry!   

Best of Luck

Hydromech
Hydraulic Systems Engineer

RE: Design Possibility, can or CANT be doneà

HST is absolutely the way to go, but flow dividers are useless in high steer angles and a high power drain to boot. Sauer-Danfoss have an electronic control and hydraulic flow control system (ASC - Anti spin control) that senses wheel speed and steer angle (2 or 4 wheel) and shuts down flow to a spinning wheel, whilst allowing for differential speeds due to steering.
Ian

RE: Design Possibility, can or CANT be doneà

keep in mind this will be for use only off road and on he rocks for rock crawling.  Wheel slippage is going to be the name of the game.  If I drive the front and rear set of wheels with a set of pumps, steering could be difficult in high angle situations if  the left or right side of the wheels are driven this significantly reduces this problem.  Also remember depending on the throtle position and configuration, it could act like a skid steer, or act like a front/rear drive vehicle with lockers.  Also depending on the situation one could utilize flow deviders and an orifaced bypass circuit around the inside drive wheel depending on which one you wanted to slip.  It does get a little complex for control and actuation, but for this application I think it will work.  Another setup, could be to look at steering angle and drive the wheels front to back or side to side depending on angle of the steering mechanism.
I have started collecting tubing, hoses, minor valves, flow controls solenoids, needle valves, I have a few actuators for suspension and steering.  I still have to get the wheel motors and pumps.  I think I will drive the pumps off a standard piston engine/funk gearbox until I can afford/justify a turbine.  I also have the bladder (reservoir) and heat exchanger that are going to be used.  I am going to put the bladder inside of a tank, and pressurize the tank with shop air for positive system return/suction pressure.  I may be able to get away with a bootstrap reservoir arrangment.  
Another arrangment would be to utilize one pump per wheel motor.  
This is obviously still in work, slowly collecting pieces and parts as I go.  I have the frame designed in Cad, but can't finalize the design until I have all the parts I am going to use.  Thanks for all the feedback and contructive critisicism.  
This is a really great site.  

Tad

RE: Design Possibility, can or CANT be doneà

tad 1299,
  You haven't mentioned a budget or where you are located-during the mid 1970's International Harvester made several models of combines that used a D414 diesel motor and most were hydrostatic drive with a C-faced mounted Eaton or Sundstrand pump(this was contrary to the popular design of belt drive pumps at this time).  The DT414 was rated at 175 hp but was capable of a lot more-some tractors used this same basic motor and it was used a lot for hotrod pulling tractors.  There are some of these combines still floating around -some with the RWA-Mud Hog.  As these models are 30 plus years old they are  not worth a lot to todays farmers and might furnish you with a power plant,pumps and wheel motors along with a lot of other parts you might need.     Good luck ,Maytag

RE: Design Possibility, can or CANT be doneà

Combines: good idea. A neighbor bought one to make into a sprayer package, and paid less than $1000 in running condition. They are not productive for todays farms, so have bascially only scrap value.

I ride Observed Trials motorcycles, and last weekend rode an event in Northern MN at a state off-highway vehicle park made from an abandoned open pit iron mine. Two square miles of blast and haul rock, from tailings to rocks the size of a car, in piles up to 300 ft tall. There are endless trails for motorcycles, ATV, Jeeps, etc. The ATV people blasting through mud doesn't interest me at all, but the rock crawlers are fascinating to watch. Trials riders have a lot in common with the crawlers: precision technique, control, traction, etc. vs. just throttle and blast through.

There was plenty of hp present, but generally they are well engineered and technical machines. Looks like a ball, but expensive!

keep us posted

kcj

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