Tire Overtreads--A Needed Invention

   / Tire Overtreads--A Needed Invention #71  
Your comment about "effective diameter" is a good one. Different track designs yield different effective diameters. In my description, I had a particular track behavior in mind which I think I explained reasonably well for us laymen. Patrick's track behavior is a bit different.

Even after caving (see, I can admit when I'm wrong and fall on my sword) as a result of the model I played with last night, I'm still scratching my head to understand why a track behaving like I described doesn't propel a vehicle like I described.

If I can find time I might build a model that behaves like what I was describing just for grins. Maybe I'll have to un-cave - who knows.

Anyway, I have to stop this - need to finish closing funding for our new company (No, we're not building tracks or overtreads)
 
   / Tire Overtreads--A Needed Invention #72  
I assume that by "a track behaving like I described", you mean either contracting or expanding to match rates around the loop. By "propel a vehicle like I described", I assume you mean at the rate indicated by the diameter of the wheel alone (without the tread thickness factored in). I think it really is as easy as you all thought in the early postings - dependent on the wheel dimeter. The flat section is irrelevant with regard to calculating rates, either of the front and back back wheel revolutions (and the ratio of those revolutions), or of the forward progress of the tractor. Its just that the wheel diameter used for the calculation is dependant on whether the outside expands, the inside contracts, or both (and in what ratio). Lets use numbers.

The wheels are 1' in diameter, and the tread is 6". The centerlines are 6 feet apart. The wheels always rotate at 1 rpm. Forward rate (in fpm) is equal to circumference x rpm. Circumference equals 3.14 (~pi) x diameter. There are 3 cases.

Case 1 - Outside dimension expands and inside dimension is constant.

This is the case of the ever unrolling carpet. The rate is equal to 3.14x1x1 because there is no slippage on the inner arc dimension, which is equal to the actual wheel dimension. Because of this fact, we use the wheel diameter in the calculation.

Case 2 - Inside dimension contracts and outside dimension is constant.

This is the case of the dozer tracks. The rate is equal to 3.14x(1+2x.5)x1 or 3.14x2x1, because the inner dimension slips around the wheel circumference in order to conform the rate of travel of the outside arc. Because this rate of travel remains constant, we must use the diameter of the wheel PLUS the track x 2.

Case 3 - Inside dimension contracts and outside dimension expands.

This is the case of the fan belt (and Peter Haydens model, probably). In order to determine the diameter for this calculation, we would need to know the ration between the rate of inside contraction and outside expansion. Lets assume the outside contracts 75% of its dimension as it traverses the arc and the inside dimension expands 25% as it traverses the arc. If no contraction or expansion occurred, the outer dimension would be 1/2(3.14x2), or 3.14, and the inner dimension would be 1/2x3.14, or 1.51. The ratio between these 2 dimensions determines the "effective arc length", so .75*3.14+.25*1.51, or 2.73. Doubling this (since the arc is 180 degrees), yields an "effective circumference" of 5.46. In this case, the rate is equal to 5.46 fpm.


PaulT
 
   / Tire Overtreads--A Needed Invention #73  
patrickg,

Nicely done - still haven't had time to diagram it. Oh well ...

Re: 2wd and 4wd

The typical track is always designed with some slack in it. This is relevant to consider ... 4wd has the potential to chew up your track badly - 2wd will not. Typically this slack is designed to account for a couple of circumstances ... mounting an object in the path of the vehicle and allowance for the fact that the rotation of the track is not smooth - it is comprised of a series of plates connected by linkages.

In a typical tracked vehicle you might consider the rear wheels driving - which pull the bottom half of the belt along - putting it in tension. This free rotates the front wheels ... but puts slack into the track on its pass along the tops of the wheels.

There's really no advantage to 4wd for a track - unless as you stated one end of the drive-train craps out. But then you're probably hurting for hydraulic fluid anyway!

When you are driving in 2wd with a track the traction is applied evenly along the track anyway -- the only thing that would improve traction would be to change the distribution of weight between front and rear axles.

This raises yet another issue - the ideal tracked vehicle would drive with the rear wheels while going forward - and the front wheels when in reverse ... you want that bottom track in tension to get the best flotation and tractive force ...

When turning, you want the rear wheel driving on the outside and the front wheel driving on the inside of the turn ...


Patrick
 
   / Tire Overtreads--A Needed Invention #74  
I guess I don't get the part about needing the driving wheels in the back (in an idealized system). If the front wheels drove they would pull tension in the top part of the track which would be transmitted around the half circumference of the rear wheels and put tension in the bottom run of track. At least in the simple idealized system. In the real world, there is slack and it would be handled easier (if you weren't allowed idlers or tensioners) if the wheel at the rear drove and and slack was in the top horizontal run of track.

This mean we agree and have to go on to something else? It happens!


Patrick
 
   / Tire Overtreads--A Needed Invention #75  
How about these:

track-torAssist.jpg


Hoss
 
   / Tire Overtreads--A Needed Invention #76  
Where in the World did you ever find that picture,I wish JD would make a small crawler like they use to years ago.
 
   / Tire Overtreads--A Needed Invention #77  
A 4000 series crawler would be great.
 
   / Tire Overtreads--A Needed Invention #78  
Pretty cool - check them out at <font color=blue>Mattrack</font color=blue>

pickup.gif


What a solution for "Best Tire for Boggy Ground".
 
   / Tire Overtreads--A Needed Invention #79  
I am more amazed everyday the info you find on this site,I already "bookmarked"grey market dozers today. Now this!!!!!!!!!
Thanks DocHeb!!!!
 
   / Tire Overtreads--A Needed Invention #80  
I think someone needs to make sure Glennmac sees that setup! I'm sure it would be the answer his boggy ground problem! /w3tcompact/icons/smile.gif Of course, it would sure play havoc with his yard!
 
 
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