Hydraulic snowmobile

[aczlan]

I've considered building a twin track sled from two junkers for grooming my personal trails. Hydrostatic would be good in that application for turning individual tracks under load & not needing more than about 15 mph. Could also power a hydraulic winch or grooming drag. Doubt it would be very practical for a general riding sled.
If you build anything please post, pass or fail. Sometimes more ultimately comes from failure than success. MikeD74t

In such a case, you might be better with 2 tracks and no skis as it would probably be hard to turn a two tracked machine with just skis.

Aaron Z

 

[Patches]

In such a case, you might be better with 2 tracks and no skis as it would probably be hard to turn a two tracked machine with just skis.

Aaron Z

It is indeed; if you've never tried riding a Ski-Doo Alpine(twin tracks/single ski)it's da-- near impossible

 

[Redneck in training]

In such a case, you might be better with 2 tracks and no skis as it would probably be hard to turn a two tracked machine with just skis.

Aaron Z

You need double variable delivery pump and two motors and steer it like skid steer or zero turn mower. For decent pulling power at 15 mph it would require minimum 40 HP IMHO. That is based on observation of my 30HP HST tractor.

 

[MikeD74T]

In such a case, you might be better with 2 tracks and no skis as it would probably be hard to turn a two tracked machine with just skis. Aaron Z

I've run Ski-Doo Alpines (twin track -single ski) and Bombardier groomers, the extremes of design. My idea, still in concept phase, is to use two chassis with two tracks and two skis, 1/2 way outboard of center on each track. I'll sit centered on & between the chassis as will the motor. The single ski Alpines are tough to steer in new snow & snowmobile tracks are too short & narrow to use without skis. Our club had a 2400 lb "Bombi" that wouldn't steer well in over 12" on snow towing a drag so a smaller machine would likely be much worse. The best answer to that problem was a hydraulic pivot on the drag hitch like a snowplow angle mechanism which caused the drag to stay centered in the tracks path on turns. I'm thinking the skis will help support the engine/drivetrain & provide longitudinal balance as well. The combination of steerable skis and individually driven tracks might work ok & hydraulic motors would be good for the track drives. Hydraulics would also allow the engine/pump/reservoir to be behind the operator which I hadn't thought of before. May never happen, if it does I'll post pass or fail. MikeD74T

 

[aczlan]

It might be interesting to tie the drive for the tracks into the ski steering. Then when you cranked the steering over to one side it, it would slow the inner track.
That might work to make the machine more manageable.

Aaron Z

 

[MikeD74T]

A yoke & wheel system similar to a light aircraft could be tied to both the skis & porportioning valves for each track would vary the track speeds coordinating with the degree of ski turn as well tying in a reversing valve. Steering, braking, forward, & reverse all in one system. Probably best to steer hydraulically as well. Makes hydraulics sound even better. Plumbing's getting expensive though. MikeD74T

 

[jjeff]

Hi Guys thanks for all the input and encouragement, Ive posted a few pictures of the donor chassis, Unfortunately its not a alpine. Currently its weight is around 300 lbs gutted, A normal sled weighs between 5-700 lbs Ideally id like to find a used 20-30 hp Kohler or Briggs V twin four stroke, preferably a 10gpm pump maybe slightly more or less. I believe from what I have studied so far i need a reservoir equal to the amount of fluid it pumps per minute correct? I noticed there are two speed wheel motors does anyone have experience with these? My plan is to keep the jack shaft and chain case which currently has a 24 tooth top drive gear (from the jack-shaft into a 44 tooth driven gear which spins a 9 cog final drive (2.52 pitch) Turning a 121 " track (If my idea works im putting in a 136" track) ideally id like to keep the chain-case and jack shaft set up as it seems easier and cheaper to change gear ratios instead of hydraulic components in order to get ideal speed and power. The fabrication for mounting the components should be fairly easy as there is quite a bit of room under the hood with the old drive system removed. For me its a matter of finding the right components that will work.In any case keep the suggestions coming and ill keep you posted. Thanks again Jeff

 

[MossRoad]

I have a Power Trac PT425 tractor. It is hydraulically articulated and hydraulically driven. It is powered by a 25HP Kohler engine. The engine spins a variable volume pump. That pump provides power to 4 wheel motors. There are two more pumps that are also spun by the engine. One is a 4 GPM pump that provides power to the steering rams and front end loader arms and a quick attach system for the implements and power angle of plows, opening grapples, etc... the second pump is an 8 GPM PTO pump to power mowers, brush cutters, power brooms, trenchers, etc...

The problem you are going to run into by varying the speed of the motor to control ground speed is that you cannot stop and start the unit smoothly. You should use a variable volume pump to drive your motor. To get the best performance, you will have to run the motor at a constant 3600 RPM. If you run it slower, you will not get any torque out of the hydraulic pump. Also, those types of engines are made to run at that 3600 RPM speed for proper cooling with their fan that is driven off the crankshaft. Too low of RPMs with too big of a load will overheat the engine.

Secondly, there is no transmission, therefore, there is no gearing. This means you have to pick a hydraulic motor that will give you either low speed and high torque or high speed and low torque or somewhere in the middle, which is moderate speed and moderate torque.

The top speed on my tractor is 8MPH. It has good transport speed across the lawn. It will go up a 25 degree slope if there is no load. If I turn on the mower, I cannot drive up a 25 degree slope. It sucks too much power for the mower. Likewise, if I pull a log up a hill, it has noticeably less power to pull me up a hill.

Some Power Trac owners that want more torque to go up hills with a load swap out the wheel motors for larger displacement motors. This give much greater torque at the wheels, but cuts the top speed proportionally. IE, if you double the size of the wheel motors, you cut the top speed in half.

My guess is that if you want to pull the weight of the machine and, say, a sled with some firewood on it over varying terrain, your top speed will not be much over 5MPH.

If you change the variable volume pump and motor to get 40MPH top speed, my guess is the thing will not have enough torque to move itself off of a dead stop.

Besides the added weight of the engine, hydraulic pump, hydraulic motor and steel mounts for all of that, don't forget you will need at least a 10 gallon hydraulic tank and 10 gallons of hydraulic fluid.

I hate to be a downer, but I really don't think it will work as spec'd.

 

[AKKAMAAN]

I hate to be a downer, but I really don't think it will work as spec'd.

:thumbsup:

MossRoad, I am impressed of how well you nailed down the hydrostatic "vital" limitations....Great experiences from the engine parts too....learned some there....:thumbsup: Thx!!

There is a possibility to get a variable motor to increase the range of speed. But that will also require an advanced pilot control system, to synchronize pump and motor.$$$$!!!

In ALL hydrostatic transmissions, even with Variable pumps AND variable motors, it is impossible to combine high output torque with high out put speed, with out using over sized horse power engines. Mechanical gearing is also definitely necessary to give provide a wider range of torque-speed operation.

A hydrostatic transmission is almost to be compared with a friction clutch in a mechanical transmission, or a torque converter in an automatic transmission. VERY narrow speed-torque range, as a part of mechanical gear transmission.

Variable pumps are volumetric in-efficient at low speed and low displacement, and mechanically in-efficient (friction) at high displacement.

Same with variable motors, volumetric in-efficient at low speed mechanically in-efficient (friction) at low displacement.

This makes the whole deal a big power loss, if poorly designed (wide range of speed-torque operation)....

BTW, hydrostatic transmissions are most useful on machinery that operates other implements, during motion, like lawn movers, asphalt spreaders, truck size mountain snow blowers, etc, because it is possible to travel very slow, with the high engine rpm's, that are needed secure high power for the implement. And also great for equipment that require exact speed and motion control, when gravity is in play!! A hydrostatic system, provides the same brake force as pull force. Great for logging equipment in difficult and sloping terrain.

I know about a guy in Israel that specializes on smaller hydrostatic designs, even bicycles....Give me a PM, and I'll "leak" his name to you! He is busy but very helpful too......

 

[MossRoad]

A few more observations...

A typical Kohler 25HP engine is about 44 cubic inches displacement, or, a little over 700 CCs. They run at 3600 RPM.

I had a Yamaha RD400 twin cylinder 2 stroke motor cycle that was 396 CCs, or about 25 cubic inches. Very similar to snowmobile engines.

The motorcycle would propel me down the quarter mile 0 to 118 MPH in 11.9 seconds.

I also had an old Ski Doo TNT 440 that would also do 100 in the blink of an eye. Never timed it, but not too many folks passed me. :laughing:

My point is...

I don't think I could remove the engine from either of those machines, install a Kohler, a hydraulic pump, a hydraulic motor, a 10 gallon hydraulic tank, 10 gallons of hydraulic fluid, etc... and get even 1/4 of that performance.

What you are going to end up with is a tracked tractor, which may be exactly what you are after. But to have any amount of torque for pulling any amount of load, you will have to sacrifice speed significantly.

If all you are investing is your time, for a learning project, then go for it. But if you are seriously going to reinvent the wheel, and have to spend money on the project, I think you should think long and hard before proceeding.

Good luck and best wishes. :thumbsup: