Why wouldn't this work?

[Rock Doctor]

Tim, The center axle idea of your's sounds cool.

I don't understand driving the rear axle instead of the front? Is it so that you have ready chain adjusters? With a sprocket I don't think the track is going to care front or back and I think there is advantage to the shorter run.

Unless you aren't using a sprocket but relying on friction and driving both the front and back tires. This really wouldn't remove chain windup. And you no long have limp home mode; I don't know how important that one is but it has been mentioned.

This ^ is what I'm picturing, it may not eliminate chain windup, but will reduce it significantly

So, last night I gave it a little more thought. The slop in the sprocket/belt cog interface (the 2 foot problem) makes stopping on a slope exciting, changing fwd/rev a little clunky, AND it will affect turning response time. I suppose I could learn to live with the first two but suspect I would really hate the last one. I think we need to design this so that the sprocket fully captures the belt (track) cogs.

Good Point

I also got to thinking about tire guides. If I put the sprocket front and back with the back still an idler then I don't need tire guides since the track is fully captured. This would create two problems. In my original design I used the tire pressure of the back tire to adjust track tension. This new design needs something else that could be a little more tricky. Worse, this new design requires the front and back sprocket to be synchronized which requires choosing a cog/sprocket pitch dependent on exact axle spacing. This means you could not make a tracking system somewhat generically usable across varying machine axle spacing.

If the back Sprocket is on an Idler, would it not "Self Synchronize" with the track?

So far I'm sticking with one sprocket and tire guides.

And about the sprocket build. Generically I've described this as a trapped tire. Okay, what I see is a tire on a dual beadlock wheel. It is important that the sprocket ends up diameter stable and, from playing with air pressure and my tires, what I have isn't anywhere close to diameter stable. So I added belting external to the tire to accomplish this. It may be that there is a tire that is already diameter stable in the air pressure/suspension range that we need. If there is then we could bolt the sprocket cogs right to the tire, add an internal protective surface, and use a tube or balls for air.

If we must rely on the sleeve for diameter stability we can still bolt this to the tire at one point to combat the tire from spinning inside the sleeve and use the same tube/ball air system.

And one more thing...

RD mentioned spinning the tire as a safe point of failure. I go to thinking about this too. Let's imagine that the track becomes totally immovable and that the engine has the grunt and that everything is break proof. What would happen? I imagine that the torque will twist the tire until the diameter shrinks enough that the sprocket pulls out of the track and skips a cog. Probably loud and scary. A big detent torque limiter. We could maybe incorporate this but I think with the machines we are talking about that the CVT will check out and you will squeal a belt, also a torque limiter.

I am continually impressed with the amount of thought forum members put into these little discussions. John, it's awesome how you can take an idea and turn it in every direction to think it through and visualize potential problems.

As I mentioned, I don't see myself tackling this idea in the near future with my current schedule, but I am enjoying the conversation..

RD

[JohnF]

If the back Sprocket is on an Idler, would it not "Self Synchronize" with the track?

Oh yeah, they aren't hooked together. DOH...

So, track tension - maybe let the back sprocket vary diameter a bit with air pressure? Won't need tire guides...

[Rock Doctor]

Ah, those are big. Don't remember those in your videos...
Yeah, those will hurt. They probably win too. Unless they shoot em.

Chicken, if you don't stand up to him/her he/she can't take you serious.

So, was just looking at tire. For me I was thinking something like the 22x11x8 turf tamer, about $70. And I imagine I would have to make the beadlock wheels.

What do you think of Tim's Idea for the Center Axles? In reality, we could probably make all 3 back axles shorter, with the angled Spindle Arm. All 3 back axles could be chained together, making a Tripple Walking Beam setup.......... Maybe, I'm still wrapping my head around the idea................. Well, OK, maybe that won't work......... BUT, if we just went with the center 2 axles, depending on the lenght of the Spindle Arm, we could use smaller tires, like 20". This would let them "walk" farther up and down.

I don't think you would have any trouble manufacturing a set of Bead Lock Rims, I did a search on those a while back, seems pretty straight forward

The only real "Show Stopper" I'm seeing here is the aquisition of the front Drive "Tires". I wonder how much space is between the Lugs on an Aquatorque Tire, and with some minor Lug Shaving, how would it fit the Adair Belted Track? The Pitch on the Adair Belted Track could be made to almost any measurement you want, and the 1.5" UHMW Grousers would certianly be strong enough.

RD

[JohnF]

His idea is cool and creates a kind of suspension. I bet he only does the middle 2 to keep track tension constant. (or near constant)

POC - get 2 of those turf tamer tires and a track system that uses open grousers; something like the Adair belted series.
Don't worry about the bead locks yet.
Figure out the tire diameter that you need to match the pitch of the tracks.
Figure out the tire pressure you need to make that diameter. Air them up. Mark lines where bars would have to be so that they pretty much capture the grouser.
Cut some bars of something (UHMW, aluminum, heck wood for now), air down tire, bolt bars on tires, cover inside so they won't kill a tube right away, mount tires with tube and put screws through wheel into tire bead. Oh, use old tires wheels - so when I said turf tamers just skip that... LOL

Take all the chains but the front off. mount everything. Run tracks tighter than you are used to. Drive around yard and take video.

[Rock Doctor]

His idea is cool and creates a kind of suspension. I bet he only does the middle 2 to keep track tension constant. (or near constant)

POC - get 2 of those turf tamer tires and a track system that uses open grousers; something like the Adair belted series.
Don't worry about the bead locks yet.
Figure out the tire diameter that you need to match the pitch of the tracks.
Figure out the tire pressure you need to make that diameter. Air them up. Mark lines where bars would have to be so that they pretty much capture the grouser.
Cut some bars of something (UHMW, aluminum, heck wood for now), air down tire, bolt bars on tires, cover inside so they won't kill a tube right away, mount tires with tube and put screws through wheel into tire bead. Oh, use old tires wheels - so when I said turf tamers just skip that... LOL

Take all the chains but the front off. mount everything. Run tracks tighter than you are used to. Drive around yard and take video.

Great Breakdown John, When you put it like this, you make me want to go home and give it a try

[Obsessed]

I don't understand driving the rear axle instead of the front?

sorry John, i should have been more clear...i would actually leave the front drive assembly alone, and just drive the front and back wheels, skipping the center ones

Unless you aren't using a sprocket but relying on friction and driving both the front and back tires. This really wouldn't remove chain windup. And you no long have limp home mode; I don't know how important that one is but it has been mentioned..

yes...i agree, i would be relying on "friction drive" as that is the best option on a fixed wheelbase machine (i could give you a lot more detail if you needed but try to keep my reply shorter)
a certain amount of chain windup is not necessarly bad if it is done correctly...it can be easier on the (new style) chain tensioners when driving forward
......Not sure this would be the weak point on the entire machine and there are lots of single parts on all of these machines that can ruin your day

So, last night I gave it a little more thought. The slop in the sprocket/belt cog interface (the 2 foot problem) makes stopping on a slope exciting, changing fwd/rev a little clunky, AND it will affect turning response time. I suppose I could learn to live with the first two but suspect I would really hate the last one. I think we need to design this so that the sprocket fully captures the belt (track) cogs..

a direct engagement tire "ring" that slips over the drive tire (and makes it function like a sprocket) that matches the pitch of the track perfectly is simple (if you have the ability to build custom track with the same perfect pitch)...nice part about that is the tire pressure would hold the ring in place and with an increased amount of air pressure would help eliminate tire slip on wheel or ring slip on tire....also nice that it does not give up water displacement on a vehicle that was designed to float

I also got to thinking about tire guides. If I put the sprocket front and back with the back still an idler then I don't need tire guides since the track is fully captured. This would create two problems. In my original design I used the tire pressure of the back tire to adjust track tension. This new design needs something else that could be a little more tricky. Worse, this new design requires the front and back sprocket to be synchronized which requires choosing a cog/sprocket pitch dependent on exact axle spacing. This means you could not make a tracking system somewhat generically usable across varying machine axle spacing..

you should look at the adair argo "fat tracks" ...very similar concept with no outer wheel guides....i actually have considered developing a custom tire that looks like a set of dual tires and traps a belt in the middle...this concept has some problems that i havent finished working through yet but i think that the idea is cleaver...i might prototype it with a custom cut set of aquatorques...

And about the sprocket build. Generically I've described this as a trapped tire. Okay, what I see is a tire on a dual beadlock wheel. It is important that the sprocket ends up diameter stable and, from playing with air pressure and my tires, what I have isn't anywhere close to diameter stable. So I added belting external to the tire to accomplish this. It may be that there is a tire that is already diameter stable in the air pressure/suspension range that we need. If there is then we could bolt the sprocket cogs right to the tire, add an internal protective surface, and use a tube or balls for air..

all non radial tires that ive studied are a lot less than perfect (in size) due to the inital factory cool down inflation process (some tires tend to expand more than others during this time and temp sensitive process)....a metal ring gives an exact size and fit and works well

RD mentioned spinning the tire as a safe point of failure. I go to thinking about this too. Let's imagine that the track becomes totally immovable and that the engine has the grunt and that everything is break proof. What would happen? I imagine that the torque will twist the tire until the diameter shrinks enough that the sprocket pulls out of the track and skips a cog. Probably loud and scary. A big detent torque limiter. We could maybe incorporate this but I think with the machines we are talking about that the CVT will check out and you will squeal a belt, also a torque limiter.

I agree...belt will be first to fail....in a hydrolic machine the pop off valves will function

the two concept vehicles that we are currently building are actually unique in the fact that the small 8 wheeler is single front wheel drive and the larger 10 wheeler is both front and rear wheel drive...the reason that i would suggest the dual tire drive on a modified argo is because any tracked vehicle with a non adjustable length wheel base is going to ultimatly have to friction drive the tracks, and it is pretty well proven that anything less than both the front and back tire driving will cause unwanted "slip" in most track designs...the exception to this is the rubber snowmobile type track that RI uses that has left over built in sprocket teeth and wheel guides making the inside of the track very rough and causes a lot of traction between the inside of the track and the tires, so much in fact that chain windup can be a really big problem with that track design and the simple fix is to remove the front drive chains and this seems to work well...

on our HT10 prototype that has four seperate wheel motors we are using friction drive of the two outer tires to drive the track...tire and track slippage can be adjusted with wheel base length and track tension...as i have mentioned before, most OEM tires repeat their pattern every 8" therefor if you want to couple the track to the tire lug for more of a chain and sprocket effect you need to have a track pitch of approx 4" and i think that you will probably notice that other similar track designs are learning from this information and adjusting their designs to match our pitch for a smoother and quieter ride. we have found the perfect pitch to be about 3.875 but have learned other factors recently and our new designs are now built on exact 5" centers (when the belt matches the tip of the tires)...

on our smaller HT8 prototype we are only driving the front tire and this could be done with a sand paddle type tire (which looks a lot like a big sprocket) if you could build a track with the right pitch, but i like the external tire ring drive sprocket better....its simple and effective and allows for common profile idler tires on the rest of the suspension, only thing is, if you are going to commit to a perfect track pitch, you have to be able to maintain track tension and tracks do eventually wear (as all tracks will if used enough)...trying to adjust this with tire pressure does not give enough size control (even durring initial fittment of tracks due to random tire sizes), and shorting the track is not an option in less than one pitch increments if it is being driven by a sprocket (unless you use a double tooth sprocket and you adjust it in half pitch increments) ....better on a new concept machine to just engineer an adjustable wheel base as is used in all other tracked vehicles whether they are spinning rubber, steel, or plastic type tracks...problem with all of these types of machines is that they are not typically built for water boyancy (and we are not building heavy bulldozers but instead lightweight boats with tracks)...

just my opinion...

tim

[Buzz]

I agree that some level of wind-up is okay. A guy should pay attention to air pressures, and general maintenance & what-not anyway. I really do think that maintaining a machine that is 8-wheel drive ( or can easily be made 8-wheel drive in the event of track problems) is important whether it be removing tracks and tuners and running straight tires.....even if the centers are tucked farther in. Getting too far away from a tire-driven machine I think is asking for trouble, but absolutely sounds cool! I find that I can never really drive fast anyway and don't seem to need suspension or "a little" more clearance.

[JohnF]

... i would be relying on "friction drive" as that is the best option on a fixed wheelbase machine ...
... a non adjustable length wheel base is going to ultimatly have to friction drive the tracks...

Friction drive should be more sensitive to track tension and harder to pull off than the sprocket drive. But I agree, and sort of bantered a bit in a previous post, that we need to be able to adjust track tension with air in the rear tire.

to wit...

...trying to adjust this with tire pressure does not give enough size control...

I don't know. Doing some quick calculations of track length and knowing my tires I think I can easily accommodate 1% track stretch. (Got a spreadsheet ) Remember, that back tire only tensions the tracks so I can start with my smallest and end with my largest.

I read one manufacturer say 1% stretch in 5000 hours. (For which product? they were vague and I didn't call)

Your guy said 1% - 2% in 5 years. And that doesn't really help us either . This year I haven't even put my tracks on. No snow where I've been.

But, if we use a 3 pitch overlap splice (no clearance issue because the splice doesn't go over the tire) then I should be able to redrill and reset grousers, trim, and put back together with a 2 pitch splice.

At 1% we replace chains so this is probably our goal for refurbishing these.

... a certain amount of chain windup is not necessarly bad ...

The physicist in me wants to say that there is absolutely no positive aspect to chain windup so all of it is "bad"; the engineer in me sees it as an understandable and acceptable compromise in the design "as engineered".

I guess I'm torn.

... a direct engagement tire "ring" that slips over the drive tire (and makes it function like a sprocket) that matches the pitch of the track perfectly is simple ...

I think so too.

... you should look at the adair argo "fat tracks" ...

Yes! Earlier in a post in this thread I mention a custom wheel that captures the guides in this tracks you have there as a drive sprocket.

I do like those and imagined a time with the sky in my windshield wondering how Tim would fair against Dan...

... all non radial tires...

Oooo, do they make a radial tire say 22x10x8? ish?

... it is pretty well proven that anything less than both the front and back tire driving will cause unwanted "slip" in most track designs ...

My observation on this:
I have supertracks. To try and obviate my tire spinning on the wheel problem I removes the back chains. It worked! The cost?: cannot climb boat ramp into parking lot where everyone is standing because tires spin inside track.

And yeah, it was unwanted.

[JohnF]

Hi Guys,

Sat down to do the math tonight.
I'm not gonna post the spreadsheet...

Conquest CC front to back axle: 72 (inches - it's a guess for now)
Max tire diameter = 23.5 (seems a good limit)
Cog depth = 1.25
Sprocket inner diameter then is fixed at 21
Start with back tire diameter of 22
This gives us a track length of 211.5442
a pitch of 4.7 gives 45 grousers and 14 spaces on the sprocket (13 cogs)

A little research shows that the snowcat folks (and the providers that service them) use a belt that has < 1.7% stretch in its life. Life being the point where the belt cracks and tears and just isn't any good anymore.

1.7% will change the pitch to 4.78 - I bet that the belt and tire and UHMW cogs will deal with this fine.
1.7% changes the track length to 215.15. To take this up I have limited myself to increasing the diameter of the rear tire and that will blow past 24!. Darn.

If I limit the rear tire to 23 inches (mine will go 22@3.5psi - 23@7psi) then I have three options (that I've thought of so far) to make this work:

1. Accept that .8% stretch is the life of the belt.
2. At .8% stretch, figure out a scheme to re-pitch the belt.
3. At .8% stretch, move the axle back 1/2 inch.

Option 1 seems a shame.
Option 2 really isn't an option but I thought I would mention it since I brought it up before. There isn't enough space to move the splice (oh, yeah - more in a bit about this) either by cutting one end or equal amounts from each without running some new holes in the belt with improper edge clearance from the old holes.
Option 3 was what Tim said. And with his help, might not be all that hard.

But about the splice - I mentioned just using an overlap. As Tim said, it does cause some problems, even in the design I mention - in this case, it wrecks the flexibility of the track where it is doubled up which will mess up clearance of tire guides etc. So, I've changed to the regular hinge splice.

Oh yeah, with Tim's help. And a caveat. I need the axle to move 1/2 inch back. If Tim made his (currently in testing) UHMW bearing (and a matching inner bearing) such that the axle center is 1/4 forward (or backward) from the current center then I could move my axle back 1/2 by unbolting and flipping the bearing 180 degrees. This makes CC = 71.75 and 72.25 and works out that I should be able to tension the track for its life. Caveat: may not be chain frendly for when you want to go back to your tires. The idea is unbolt, turn. rebolt without the need to pull the axle. Perhaps when going back to tires we point the offset up which might makes the chains happy??? I haven't actually put eyes on this but I think there is room in the axle tunnel for this.

EDIT: I should mention that the UHMW bearing just came to mind. A bearing flange for the inner and outer bearing with the 1/4 inch offset would do the same thing.

EDIT AGAIN: Works out better if we can go +- 3/8

[Beeman]

Couldn't you just change out the UHMW cog when the belt reaches (lets say .8%)? If the track stretches at the same rate across the length, than you'd just have to have a cog with a larger pitch (and larger dia, whatever that would be). Seems easier than to move an axle back.

This sounds like something I can easily cut out on my CNC table.