If you designed it today, what differential would you use?

Assuming the basic drive system Thiokol used (shaft input drive), what modern skid steer unit would you use now?

Sort of contemplating building a diesel powered cat with more ground clearance but able to use existing drive sprockets and track parts, 1/2 shaft torsion axles, larger boggie wheels, and 5 boggies with front idlers.

No idea is too simple or too radical. Throw your thoughts out for everyone to think about.

for ease I would grab a bobcat power train if you use half axles don't waste your money on the junk at harbor freight south west trailer sells some good ones I believe mn outdoors have something about the same unless you have time for a big project I would buy something al ready engineered.

Isn't the Bobcat a wheel motor design?

Good basic writeup on bobcat (skidsteer) drivetrain here: http://science.howstuffworks.com/transport/engines-equipment/skid-steer2.htm

ob cats I have worked on are all pumps and hydro motors attached to a chain cat has a cool new hydraulicly operated steering diff uses a motor to enact variation between tracks but they are much too heavy and large I think the weasel ale is an affordable option but as we have learned they have weak axles where they work real good in a weasel size rig they don't scale up too well which leaves either bombardier or oc axles both are obsolete but reliable. may be an axle out of a small Kubota tractor may work I don't know how the differential works is it brake steer or a controlled diff like the oc series

I like simple. The more complex you make things the harder it is to engineer everything to work correctly.

Unless you have a skid steer to start from scratch with, you are buying a lot of $$$ parts. You specified some guidelines but I'm going to make some arguments against the platform design you want to use.

Hydrostatic drive is proven to work but they have some major drawbacks. For one, if you run out of oil, they sit until you get more. They take warm up time before you can drive in the cold. They require cooling, since they are making heat all the time when under load. When the oil is cold, you have to be careful, when the oil gets too hot, it burns up or causes failures; water contamination from an unforseen dunking could be $$$ burning up motors, pumps and corroding everything in sight unless you can get all the water out.

Automatic transmissions are also pretty iffy for me. While they are convenient, they waste HP and make heat. Even if you got a lockup torque converter, there will be inefficiencies and more moving parts. Although the modern ones are pretty reliable and strong, they are a very inefficient way of turning fuel into heat and when something fails, they may strand you right there.

Turning brakes that are dry will not work correctly without some very big components to dissipate heat. Wet brakes are strictly tractor type stuff and bring huge weight penalties with them.

Variators are a cool design but the modern versions are big $$$$.

Personally, I favor the Tucker 4 track design for anything I built at home. Simpler, can be made out of junkyard parts and pretty robust.

Although I am working on a Sno-Trac, if I built one at home, I would build a Tucker clone.

There is a reason that you don't see hydrostatic drive pickups going up and down the road, as said before there heavy, make heat and waist power. I think the secret to building a killer snow cat is keep the weight down and use a drive train that is already engineered. For the frame I would use chrome molly tubing. (again there is a reason they use it to make dragster frames, incredible strength and very light weight ) put the aluminum front differential out of a S-10 size pickup in the front and back. Then you could use 4 after market style rubber track units (already engineered ) I would power it with a all aluminum V6 diesel, 8 speed automatic, and transfer case out of a Grand Cherokee Jeep. (425 ft lbs of torque) If you run it in low range it would be geared low enough and still be able to move out (30 mph). Put this under a 50's style aluminum Tucker body and you've got it. 4000 lbs ( trouble with this plan is you you would have to be a electronical engineer to be able to make these computer controlled motors run)

Snowtrac Nome said:

ob cats I have worked on are all pumps and hydro motors attached to a chain cat has a cool new hydraulicly operated steering diff uses a motor to enact variation between tracks but they are much too heavy and large I think the weasel ale is an affordable option but as we have learned they have weak axles where they work real good in a weasel size rig they don't scale up too well which leaves either bombardier or oc axles both are obsolete but reliable. may be an axle out of a small Kubota tractor may work I don't know how the differential works is it brake steer or a controlled diff like the oc series

Click to expand...

The Bombardier differentials are still being made (10,000 new ) we are building a new J5 style machine for firefighting this winter

I have seen hay swathers converted.

willd said:

if you run out of oil, they sit until you get more.

Click to expand...

It has been my experience if you run any mechanical device out of oil it sits until you get more??

tatman said:

There is a reason that you don't see hydrostatic drive pickups going up and down the road, as said before there heavy, make heat and waist power. I think the secret to building a killer snow cat is keep the weight down and use a drive train that is already engineered. For the frame I would use chrome molly tubing. (again there is a reason they use it to make dragster frames, incredible strength and very light weight ) put the aluminum front differential out of a S-10 size pickup in the front and back. Then you could use 4 after market style rubber track units (already engineered ) I would power it with a all aluminum V6 diesel, 8 speed automatic, and transfer case out of a Grand Cherokee Jeep. (425 ft lbs of torque) If you run it in low range it would be geared low enough and still be able to move out (30 mph). Put this under a 50's style aluminum Tucker body and you've got it. 4000 lbs ( trouble with this plan is you you would have to be a electronical engineer to be able to make these computer controlled motors run)

Click to expand...

So your vision is to build a tucker-like rig then? Are you planning to use hydraulic assist to get the front end to turn or articulate the frame like Tucker did?

MNoutdoors said:

The Bombardier differentials are still being made (10,000 new ) we are building a new J5 style machine for firefighting this winter

Click to expand...

What did Bobardier use as a differential?

In my mind, there must be a lighter weight planetary differential with wet brakes than the C-4 C-12 stuff, and output reduction with drops would help get the rig up out of the snow.

I know there are direct wheel motors capable of providing drive to a rear sprocket, but I don't have the hydraulics knowledge to figure out what size would be needed. Plus skid steering changes the motor size due to the added drag when in a turn. I'm not patient enough anymore to self teach myself what I'd need to know.

I have never been a fan of the Bobcat chain drive system either. Just seems sort of flakey to me.

Here is my 1404 with highly modified drive/track system. I think it is 1500 parts, but not positive.

If anyone knows more of this rig, I'd appreciate any history on it. I bought it in 1987 or 1988 or thereabouts. It works, but it struggles in deep snow due to under-powered with the V4.

Alaska Snow Cat said:

It has been my experience if you run any mechanical device out of oil it sits until you get more??

Click to expand...

Yes, but in the case of Hydrostat's for something the size of a cat, you are talking about 20-30 gallons of the stuff. I can haul in a couple gallons on foot or snow machine pretty easy. Figure 60% of capacity for a minimum and you are looking at hauling 12-18 gallons of oil, just to get the machine out of wherever you broke down at.

If money is no object and you wanted portal axle drop boxes, then running Unimog axles or the ultra $$$ bolt on drop boxes for a 14 bold GM rear would get you up out of the snow.

I really think you should go to a couple of tractor dealerships and look at some AG tractors. They have some really good ideas and many of the rear axles for tractors can be modified to run a different power plant in front of them.

The one big drawback besides $$$ is the weight.