amphibious drive

[metinker]

I've been thinking about amphibious vehicle design and it seems the greatest challenge is the land drive wheels.

Prior art seems to mostly consist of truck axles. Rudimentary and lots of places for water to penetrate and damage bearings, brakes and gears.

Later generations apear to be CV type axle shafts outboard of the hull. Better because differentials and brakes can be isolated from water. Still alot of potential for bearings to be contaminated and certainly doesn't lend itself to salt water.

What other ways might there be to support wheels and tires while applying a driving force?

 

[ivymike]

you've covered shaft drives, so
gear drive
hydraulic wheel motors
electric wheel motors

 

[4xWriter]

I knew a guy who played with WWII era Ducks (DUKWs) in the '50, '60s, and '70s, turning them into motor homes and taking them up to Alaska, sometimes by water up the sound. He made various mechanical mods over the years, from diesel engines, Allison automatic, conversion from 6x6 configuration to 4x4, etc. He found the axles were a big drag in the water, not to mention a maintenance nightmare. He tried going to 4x2 configuration but found he needed the traction from the front wheels to get out of the water. In the end, he developed a hydraulic drive for the front... just for the low speed work. The rear axle drove the vehicle on land bur the hydraulics up front provided the extra pull to help the Duck waddle out of the water. I never saw the ducks at that point, so I can give you any detail, but perhaps you can take the idea from there.

Jim Allen
Keeping the Good Old Days of Four-Wheeling Alive

 

[MikeHalloran]

I'm told that some Florida swamp buggy axles are lubricated by mud. I.e., they just cut a window in the top of the banjo, and let whatever liquid is not needed for immersion lubrication spill out. ... but they move slowly, and don't see much dry land.

WRT to more modern DUKs and similar, it should be possible to just pressurize the housing, e.g. by connecting, say, an electric smog pump to the axle vent.





Mike Halloran
Pembroke Pines, FL, USA

 

[metinker]

Thanks for the input so far.

Might be horribly inefficient but dont know. What about some type of thru hull magnetic drive like a stereo turn table or one of those stirring rods from chemistry class? could it be rigged for regen braking?

 

[ivymike]

how about just retracting the wheels into the hull and covering the holes?

 

[evelrod]

Amphibious drive is going to be problematical, no matter. Even the boat trailers I built in the 70's could only be partially "cured" (double, back to back seals and pressure luber}...still requiring extraordinary maintenance. The local Marine Corp base at Pendleton do a complete tear down after every exercise involving their amphibious vehicles. Something close to that level of maintenance is what will be required for you, is my bet.

A google turned up several "retractile" designs, but none isolating the drive from contact with the water.

Rod

 

[MechEng2005]

Design the vehicle such that the water never reaches the center of the wheel. Then you only have to worry about splashing and rocking and such. It should be easier to seal bearings and the like from splashing than from submersion.

 

[GregLocock]

So how did the Amphicar solve this?

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[evelrod]

In my experience, what I have seen in the few Amphicars that actually got wet, they have not solved the problem.
I watched a History/Travel/Whatever channel program on amphibs a while back...A really fast waterjet Fiesta with retractable front wheels and a giant 40 foot motor home converted. I did not see ANY reference to maintenance...Kinda makes one wonder when all they make issue is the "bilge pumps"!

I am not a 'boat person' but, I live not so far from a big salt water lake and I have never seen ANYTHING come out of it without the need of maintenance, and immediate, at that.

Rod

 

[vwhammer]

I believe to make this a truely reliable system it will need a combination of methods that will help where ever they can.

I might sugesst a hydrofoil arrangement combined with retracting wheels and a redundant sealing system.

With the hydrofoil once you got up moving in the water the wheels would not be submerged.

 

[evelrod]

Yes, I believe that was pretty much the waterjet Fiesta method.

Rod

 

[bluebeast]

Portal axles!! The VW thing used them so maybe you could adapt those to your project and be cheap or you could go with the Hummvee ones $$$$ It depends on your freeboard height but say you have a portal axle that is 1 1/2' from input to output, You could have the axle connected with an air spring and then swivel it so it would be out of the water and give suspension (swing arm style) when on the road. Using them will have the input (through hull part)
higher up (even if not out of water completely) will reduce the amount of water pressure on your seals. I would use a stuffing box set up with a zerk to keep that sealed.
The idea of using pressure to keep water out is a good idea, but if you could swivel the portals then it would be that much less to worry about.(less time tearing down)

 

[dashrr]

You may want to check out a central lubrication system available from manufacturers such as Vogel(a division of SKF). I have experience with operating vehicles in harsh underground mining environments where wheel bearings are frequently replaced. The Vogel system has been demonstrated to eliminate the need for frequent bearing replacement by maintaining a positive pressure or delivering an amount of grease to the bearing at specified intervals.

 

[Apakrat]

Perhaps adapting a hydraulic drive system simuliar to that being discussed at

http://www.eng-tips.com/viewthread.cfm?qid=237688&page=1

would be a solution............

At 74th year working on IR-One2 PhD from UHK - - -

 

[dalcazar]

This sounds even more rudimentary and crude than most of the options listed so far... but what about belt drive?

It would be fairly easy to isolate everything up to the drive pulley and all you have exposed is the pulley itself and the recieving pulley on the wheel, couple them together with a solid rear axle which can be hydrodynamically designed and you just got rid of a lot of drag.

You'd need to mount everything inboard of the pulleys including the diff, and then seal it all off. The only seals you have to worry about are the pulley shafts.

The problem I see you having is powering the front wheels and keeping them steerable. Perhaps the afore mentioned "traction for exiting the water only" with a 4WD gearbox that you can engage for front wheel traction.

 

[berkshire]

"Later generations appear to be CV type axle shafts outboard of the hull."
This appears to be Yamaha's system with its latest toy. The Quadski - ATV and Jet Ski in one!

It is interesting to note that they are popping in and out of fresh water not salt water in their video.I have a feeling that salt water will tear this up in no time.
B.E.

 

[patprimmer]

My experience is with inboard boat trailers where the boat must be floated off the trailer.

The worst situation is immersing in cold salt water while still hot from road travel. The sudden temperature drop sucks salt water past the seal. If it is run again quite soon after it is not to bad for a while, but if it stands for a week or two then the bearings take a real hammering.

The systems that reduce maintenance from extremely high to reasonably high are:-

Pack bearings with copper coat grease.

Use hub grease caps with a spring loaded piston built in so the bearing is always full of grease with some pressure applied to the grease.

Use a fitting into the rear seal that supplies ATF to the bearings from a reservoir well above water level at all times.

Use a hub cap with a clear window, preferably in combination with some of the above so that water ingress can be observed to trigger maintenance before a bearing collapses.

Allow cool of time before imersion.

Use top grade lip type seals, lube seal lips and stubs on assembly.

Keep stubs well polished so as not to damage seals on assembly or on start up.

Never be afraid to waste a little grease or to have some excess grease make a bit of a mess.

What do they use in the shaft seal for an outboard motor propellor shaft.



Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[metinker]

Thanks everyone for the input so far.

 

[amorrison]

If the items in the "volume of interest" were beforehand pressurized with about one psi gage of air then no leakage would occur.

The one psi would be good for a ~two foot depth.

One atm = 14.7psi = 33.9 ft of water head.