Help with Chain Link Spacing?

[xenologer]

I've recently purchased 8259 Mini Bulldozer, which is my first set to contain caterpillar track / chain links.

I was wondering if anyone could help explain the spacing of the chain links to me, and how to make them mesh properly with gears and wheels and whatnot.

They don't appear to be any obvious stud length, and the official model has them quite slack so it's not the best reference point...

I guess basically, is there a formula that can tell me, given 2 gears of x number of teeth and y studs apart, how many links to encircle them perfectly?

[Siegfried]

I've never heard of any for any of the LEGO track systems. Are there? When I made my Mobile Still I just kept adding until it fit and spun well...

[Blakbird]

I've recently purchased 8259 Mini Bulldozer, which is my first set to contain caterpillar track / chain links.

I was wondering if anyone could help explain the spacing of the chain links to me, and how to make them mesh properly with gears and wheels and whatnot.

They don't appear to be any obvious stud length, and the official model has them quite slack so it's not the best reference point...

I guess basically, is there a formula that can tell me, given 2 gears of x number of teeth and y studs apart, how many links to encircle them perfectly?

The reason for the size of the chain links goes back a very long time....

In the beginning, there was Expert Builder. And LEGO saw that it was good. On the second day they created 3 sizes of gears, 8 tooth, 24 tooth, and 40 tooth (which still exists to this day). The gears were not ashamed that they were gray, for they all meshed together perfectly. This was because all gears used the same tooth profile, and the diameters of the gears were designed both to allow for an integral number of teeth and to allow them to properly mesh when spaced out with Technic beam holes. And the evening and the morning (of 1977) were the second day. On the third day (of 1979) LEGO created chain links in both tread width and chain width. These were included on the 856 bulldozer and the 880 motorized expansion pack. The links had to be sized to lock securely over the already standard gear tooth size. This means they are not exactly an incremental size of a regular brick, but they do work with the gears. Even modern gears still use the same tooth size. The new treads like on the big bulldozer do not fit over gears, they fit over special spools.

After the sixth day LEGO decided to rest and the evil MegaBloks appeared and stole their patent. But not to worry, the son (and grandson) unto the third and fourth generation of the LEGO founders would eventually come to crush the head of the dark one.

All of this is well known and recorded in the sacred texts.

[xenologer]

Thanks for the info, helped me reapproach the problem.

Letsee then: If chain is based on tooth length, not stud lengths, then to determine how to make a perfectly no-slack chain loop I need to find the conversion from teeth to studs.

Looks like that should be easy:

Given that conversion, now it should be easy to calculate the circumference of a given loop in teeth units... which means all I have to do is figure out which loops produce circumferences that divide into integral numbers of chain links...

[Blakbird]

Letsee then: If chain is based on tooth length, not stud lengths, then to determine how to make a perfectly no-slack chain loop I need to find the conversion from teeth to studs.

Given that conversion, now it should be easy to calculate the circumference of a given loop in teeth units... which means all I have to do is figure out which loops produce circumferences that divide into integral numbers of chain links...

That should work, but keep in mind that there is a limit to how tight you want the links. Any unsupported span is going to have some droop. You can minimize it with tension, but not eliminate it. If you make the tread tight, it will also cause friction and binding in the drive gears. A better solution is to either:

• Put in an idler gear to support the sagging area, or
  
• Spring load one or both drive gears to generate a constant (small) tension.
  

[CP5670]

I tend to simply do this by trial and error. As Blakbird said, you will often run into situations where you cannot get an exact fit over two gears, but a small amount of slack in the chain is usually fine.

[Capt. Stabbin]

I just finished the 8047 compact excavator, and i can't get the darn thing to roll on anything but carpet. I havent had any time to try and fix the problem though. Probably some thing to do with chain link spacing? You would think lego would do a better job!

[dr_spock]

I've recently purchased 8259 Mini Bulldozer, which is my first set to contain caterpillar track / chain links.

I was wondering if anyone could help explain the spacing of the chain links to me, and how to make them mesh properly with gears and wheels and whatnot.

They don't appear to be any obvious stud length, and the official model has them quite slack so it's not the best reference point...

I guess basically, is there a formula that can tell me, given 2 gears of x number of teeth and y studs apart, how many links to encircle them perfectly?

I use trial and error. If it is too tight, I'll add a link. I re-used the tracks and base from the mini dozer B model for a little Lost in Space MOC. I added a couple of small wheels on smooth pins to take up the slack. The tracks seem to roll pretty well on my desk and bed.

[backbone]

I just finished the 8047 compact excavator, and i can't get the darn thing to roll on anything but carpet. I havent had any time to try and fix the problem though. Probably some thing to do with chain link spacing? You would think lego would do a better job!

Add some wheels, it works. But this model looks better standing on bookshelf

[telecasterman]

I guess basically, is there a formula that can tell me, given 2 gears of x number of teeth and y studs apart, how many links to encircle them perfectly?

I usually just let Lsynth tell me how many I need, then order a few extra just in case...