tracked vehicle differential questions

[SensibleNick]

Bunge cord WILL be ineffective in cold temps. I had a little plane with that setup and it goes stiff in the cold. It's rubber. But you are right, the idea is cheap and tuneable.

Open disk brakes freeze and are completely useless if bathed with snow. They must heat up, melt the snow which again freezes on the pads. I use a tracked ATV with inboard disk brakes and they do freeze if there is enough snow to fly around. You don't really need brakes though, so it is not a problem. That's why I like articulating cats instead.

Very glad to learn from your experience here Jim. I had wondered, but been unsure when it came to bungees, and the disk thing was mere speculation on my part
Coilsprings it is (for me).... :licking:

Since I last wrote here my ideas have turned towards hydrostatic drive.... negating all need for brakes

 

[SensibleNick]

... but then again... Does cold temperature affect the elasticity of a rubber band?

http://www.answerbag.com/q_view/2228701

Two nearly identical questions, two contrasting answers ....
I think I'm going to have to conduct my own tests

 

[davedj1]

I'm not terribly worried about the brakes, won't be going in that deep of snow, no worse than driving in a snowstorm.
With mostly slow speeds in the trails, I'm not sure if springs will be necessary or not.
Keep the info coming, it's nice to dream about what someday may be a reality.
thanks,
dave

 

[SensibleNick]

I'm not terribly worried about the brakes, won't be going in that deep of snow, no worse than driving in a snowstorm.
With mostly slow speeds in the trails, I'm not sure if springs will be necessary or not.
Keep the info coming, it's nice to dream about what someday may be a reality.
thanks,
dave

...If you were to chance it and go for the disks (it's what I would do in your position) you could always try that idea of routing the exhaust right up to them to keep them nice and toasty ... could even take the exhaust pipe itself though the cab and have yourself a nice hot radiator

you may be underestimating the amount of snow that'll be there though. Everything that sticks to the tracks seems to end up going around the wheels inside. Watch the videos again: the disks will be constantly showered with snow...

 

[jetboat]

have you considered using WIDE tires instead of tracks? Look at the artic trucks they use. Would make the design allot easier.

 

[jimgerken]

I'm not terribly worried about the brakes, won't be going in that deep of snow, no worse than driving in a snowstorm.
With mostly slow speeds in the trails, I'm not sure if springs will be necessary or not.
Keep the info coming, it's nice to dream about what someday may be a reality.
thanks,
dave

You don't really need brakes for stopping. I was commenting on the freezing brakes issue because I was afraid you were going to build something intending to brake-STEER, and I just know you will not have good enough brakes to steer once they get bathed in flying snow for a while. Unless you can put them well inboard where they do not get snow on them, and I am suggesting totally enclosed, with ventilation from a known dry source.
When I am out on the aTV with tracks, the brakes are inboard but open, a good foot off the ground to the lowest point on the disk, and they freeze and are worthless, and I generally don't care because the tracks add so much drag to the driveline that to stop I just stop applying power (I am pulling a rolling groomer). IF I need brakes bad enough, and plan ahead, I can ride the brakes for 100 feet to thaw them, then they are wet sounding (stiction effect) and they do work OK.
Suspension, I agree it is optional if traveling less than 15 mph in the snow, either breaking trail or running on broken or groomed trail. At that speed, you are essentially a tractor. Add an air ride or at least suspended seat if you later find it uncomfortble. Let that decision go until it proves itself to be needed, in other words.
I always wanted to build a small articulating snow cat. With tiny heated cab for one person, hitch for groomer, place for a chainsaw, etc. Still will build one if I live long enuf.

 

[MikeD74T]

....I always wanted to build a small articulating snow cat. With tiny heated cab for one person, hitch for groomer, place for a chainsaw, etc. Still will build one if I live long enuf.

Me too, but I'm beginning to think I'm on the wrong end of living long enough..... MikeD74T

 

[oughtsix]

Have you guys considered using a leaf spring or two as the "Beam" part of a walking beam suspension? The middle of the spring where the axle usually mounts would be the pivot and you could probably use the spring perch that came with the spring to help fabricate the mount. The idler wheels would then be located at each end of the spring. This would give you a little bit suspension without much hassle. You could probably even make use of the rubber spring bushings to help isolate some of the small vibrations from the cab?

Fortunately we are blessed with a wealth of wrecking yards here in the USA and leaf springs are very cheap if you ask yard attendant nicely.

How are you guys envisioning tensioning the tracks? With air filled drive tires it is a simple matter of adding / removing air. It seems you could end with a lot of unneeded complexity if you aren't careful about your design.

I have always wondered if you could find a big enough set of old agricultural floating tires if you could cut the tread off the tires and use the tread as a basis for the track?

 

[SensibleNick]

How are you guys envisioning tensioning the tracks? With air filled drive tires it is a simple matter of adding / removing air.

Bare in mind that Dave has one idea, and I've offered advice based on what *I* plan to do. 2 different projects on 2 different continents, and I reckon that he and I are about as likely to "get 'er done" as each other

My tracks will be coming from a BV202 (retired Swedish army machine, also used by the Brits I think). Their tracks are usually tensioned by sliding the rear bogey wheel back - pretty much the same as any tracked excavator.

The tracks are rubber moulded over steel cable and cleats, allowing the machines to drive on roads and into cargo aircraft without damaging them.

Drive is provided by the elevated front sprocket. In my case driven by a hydraulic wheel motor on each side. For tension I'll either move the motor mounts or shove the rear wheel back a bit, but I won't have to deal with slop or play in the tracks like a steel-shod 'dozer would.

Here's a BV202 so you get a rough idea of size of the tracks. I'd imagine Dave's machine will be bigger. (I'm only after a single set of tracks)

 

[oughtsix]

Hi,

Sorry to drop in on the thread. I enjoyed the videos that were posted a few pages back... some really cool vehicles there. That swamptrax thing was just amazing.

I realize that there are a couple different projects in this thread but it seems like there are some common problems to overcome... and I really enjoy pondering such things.

Are you going to be able to get the tensioning bogie wheel off of the machine you are going to get the Tracks off of? I certainly would if it were available! If a ready made solution isn't easily scavengeable it seems like it might present a considerable engineering issue.

Personally I like the hydrostatic solution. I even have a brand new dual hydrostatic skid steer pump in my shop and several wheel motors and a couple torque hubs for a wheeled project that is moving VERY slow. All were some great ebay scores over many years but the hydraulic stuff can be very costly!!! I haven't even started looking at hydraulic lines and fittings for my project yet. Once you start adding all of the hydraulics up I can certainly see the cost advantage to a differential and independent brakes.

I am currently banging my head on the easiest way to couple my dual variable pumps to a 1.6l toyota engine without loosing the starter mount.

 

[SensibleNick]

So long as you know we're not all talking about the same thing

The original tensioning system on the BV202 is fairly hefty, and the BV202 is a far heavier vehicle than I have in mind for my toy... so it'd be overkill.

Tracks are relatively easy to come by (here in Sweden), but the machines themselves are like hen's teeth or redicilously expensive when they do come along. Besides... butchering a working machine for just one part would make me feel bad.

Yes, it'll be an engineering challenge, but compared to things I design daily it's a fresh breezy walk in the park with a zz-top soundtrack. I won't be breaking any new territory, but I'll be able to do things *my* way - Most likely scenario is moving the mount for the drive wheel. Given that I'll probably end up messing about with different drive solutions, having a modular unit at the drive end of things is a nice way to ensure I don't have to hack the entire pontoon about each time I want to try another drive system

PS... I hope Dave agree with me on this one, but as this is not a build thread, and seems to be more along the lines of what you say in your last post - dissecting the issues one by one and mulling over the ideas involved in making something like this happen. As such (from my part at least) there's no need to apologize for poking ideas, questions and suggestions in - it's all welcome and would help us get to a better solution in the end.

 

[davedj1]

Yes, it's good to have many minds mulling things over. I'm no engineer but enjoy building things. I enjoy reading what other people are thinking, doing and wishing they could do.
At least when the time comes to actually start the builds we will be much more informed and hopefully have some better ideas of what we want/need to do.

thanks guys, keep the good words coming,
dave

 

[oughtsix]

Cool, I enjoy mulling things over.

Dave am I correct in my understanding that you are thinking of using a Samari motor for powering the vehicle? Are you considering using the stock trans axle? This seems like it might be a problem as I believe there is a transfer case with a rear facing output shaft to drive the rear wheels??? Would you just be able to ignore this output shaft? Do you have a 2wd Samari you are thinking of using?

Nick, what are your thoughts on the power unit for your vehicle?

 

[SensibleNick]

Nick, what are your thoughts on the power unit for your vehicle?

I know it's a more expensive option, but I want to make an "easy to use" machine that my young lad can use when he grows up... so hydraulic drive is on the table here.

I had been considering the $1800 stack of pumps that Surplus center have.
(go look at their HST pumps and you'll find a pair of variables mated to two gear pumps).

I then realised that that setup was totally "overkill", and took a single step up their list to the 1.10cu pumps. A pair of those driving a pair of the smaller wheel-motors they have should give me 30mph (plenty) and some massive torque. (Which equates to the top of each track being pulled along with a force of 1.5 tons)

For the other hydraulic pumps Something small and v-belt driven will fix the auxiliary bits and bobs (8gpm?) and a larger pump coupled to a PTO-splined motor.

I'm wondering whether I should go gear-pump and spool-valve for the PTO system, or HST pump?

The Engine... Originally I wanted 100bhp (seemed like a good figure) but now I think 60bhp is more realistic. I won't be using full drive capability AND full PTO power at the same time - it'll be one or the other.

So a 1.5 diesel will do the job. Maybe something from a small french FWD car? Peugeot or Renault... or maybe the ford 1.8D?

I'm not decided on that one really.. though it MUST have a mechanical injection pump for simplicity. A Turbo might be a bad idea given that I want low-down grunt.

I don't need to retain the clutch, so the hub of the flywheel can have a CV Joint mounted on it, and the Pumps can be driven from a simple pillow-blocked driveshaft using rear sprockets from motorbikes and some decent chain (usually good for 100bhp applications, and more efficient than belt-drive).

I considered dry-sumping the engine too to get the Center of Gravity lower... and then I realised I was getting carried away... though with this machine probably getting some time with it's nose or bum high in the air, maybe it's a good idea.

Fun anyway. I find meself stood in the shower at the end of the day, whistfully staring out of the window trying to get a good idea of the control layout on it and trying to work out how much use it'll be.... :ashamed:

 

[davedj1]

I am contemplating using a Suzuki Sidekick, 96 ish. I am planning on doing away with the front axle completely and running it from the rear. I'm hoping to leave the steering wheel and somehow rigging the brake master cylinders so it will brake steer when you turn the wheel.
I will lose the rear suspension, moving an axle down and mounting it solid to drive the tracks.
I wish I knew how to use an auto cad program......LOL
I still do things the old fashioned way, a sketch pad and some trial and error.

Nick, we (our snowmobile club) has a Cushman Trackster that has the dual pump/motor setup, it runs off a joystick and is very responsive. You have to be careful! If it was up to me I would have made it into two separate control levers. After the engine swap it took forever to get the linkage lined up perfectly so everything would work as it should.

 

[SensibleNick]

hmm... Joystick V. dual Lever....

I'd probably play with both layouts, but in the name of simplicity the joystick will have to wait. If I manage to make it "fly by wire" as I hope, then joystick becomes easier as I can program in a less sensitive control system if needed, or essentially a digital "difflock" to ensure it only goes straight when I want it to. The limits are endless to be honest.

But to start with... two levers - there's something very pleasing and basic about two levers.

 

[Iplayfarmer]

...I had been considering the $1800 stack of pumps that Surplus center have.
(go look at their HST pumps and you'll find a pair of variables mated to two gear pumps).

I then realised that that setup was totally "overkill", and took a single step up their list to the 1.10cu pumps. A pair of those driving a pair of the smaller wheel-motors they have should give me 30mph (plenty) and some massive torque. (Which equates to the top of each track being pulled along with a force of 1.5 tons)...

I've mentioned this before, but I don't recall if I've mentioned it on this thread or not.

Look into golf course reel mowers. You have all the parts you need: Wheel Motors, hydraulic pumps, power steering valves, hoses, etc. You can likely pick up a broke down reel mower for pretty cheap and leave more money for other parts of the build. I have three sitting in the back of my pasture that I am still scrapping parts from. I'm assuming that they have golf courses in Sweden.

 

[SensibleNick]

I've mentioned this before, but I don't recall if I've mentioned it on this thread or not.

Look into golf course reel mowers. You have all the parts you need: Wheel Motors, hydraulic pumps, power steering valves, hoses, etc. You can likely pick up a broke down reel mower for pretty cheap and leave more money for other parts of the build. I have three sitting in the back of my pasture that I am still scrapping parts from. I'm assuming that they have golf courses in Sweden.

We do have golf-courses, but most are mown with tractors. The other thing to consider is that the entire Swedish population would fail to fill London in the UK. There are 2 million too few people to do the job. Golf course concentration is fairly low.

Part of the fun for me is building from scratch and being able to spec components that I want to use. Although shipping a crate from the US is going to hurt financially, the vast array of tasty goodies that SurplusCenter has is stunning - and makes it all worth while.

Given that I've managed to "save money" by going the cheaper pump route, I can also add some extra goodies to the package: 3 cylinders for the front 3-ppoint (allowing for top and tilt) 1 cyl for the rear 3-point, and a pair of cylinders for the snow-pusher's wings. :licking:.... might just have to buy myself that plasma-cutter too

 

[Iplayfarmer]

Part of the fun for me is building from scratch and being able to spec components that I want to use.

Understood. I can totally respect that.

Part of the fun for me on a creative build is re-purposing old parts rather than buying new. For some reason I feel like I get extra creativity credit for using old parts.

 

[davedj1]

I wish we could "find" used equipment like a golf course mower, they must go to employees as I never see anything up for sale. Maybe I should stop by and ask, there are about 6 of them in a 30 min radius.