Hardwareless Toy Caterpillar Tread System

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Hardwareless Toy Caterpillar Tread System

Postby EricPeterson » Tue Jan 23, 2018 5:06 pm

It occurred to me one morning it might be fun to design a hardwareless caterpillar tread assembly -- links that would simply snap together with a proper over-rotation and slide into place. No deformation... no bending... just fold them back into a relative angle they'll never see installed, and <click>.

Here's the second draft design:

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My first prototypes were in ABS, but the shrinkage and deformation is inconsistent with the needs for some tolerancing and clearances to allow for relative motion:

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My next prototypes were in PLA. Not as strong as ABS, not as tough, but they only take a minute to clean up each and I got good free motion, no sticking, no locking. They move so freely, in fact, that a short loop will circulate-roll down an incline properly, without wheels, given sufficient traction.

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I printed a few evenings' worth of links, plus the prototype wheels. One's a drive cog, and the other is a bogie/idler. It's important to scrape off support residue on the inside flanges, especially inside the main flanges and each side surface of the cog teeth. Given good cleanup, you get really nice motion, no sticking, no catching. The wheels are designed to mount up to a regular, common, dirt-cheap-if-you-don't-have-any AC Gilbert or Gabriel-era Erector Set flanged hub. The older one-piece cast AC Gilbert-era brass hubs are the nicest, but I built in little recesses for the protruding hub end in later pressed 2-piece assembly tin flanged hubs.

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Anyone can download the STL files here:

http://www.scifiwheels.com/images/M2Parts/treads.zip

Each file includes an 8-layer ( at .08 mm ) build platform under the part with an .050" gap for adhesion to your build platform and stability . The units are inches, and full scale gives you a 2" width tread. The wheels are designed to support the tread segments all the way across their width, so the support discs and grooves aren't symmetrical about the tread centerline. If you print without soluble support and are worried about cosmetics, I've included both right- and left-handed print versions of the wheels -- so two versions of the cog, and two of the bogie. The only difference is the end under which the support platform is placed, so your finished top layer corresponds with the end of the wheel that supports either the right or left edge of the tread.

Enjoy.
EricPeterson
 
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Re: Hardwareless Toy Caterpillar Tread System

Postby EricPeterson » Wed Jan 24, 2018 5:53 pm

Note: I'm getting better performance out of the test set when I decrease the width of the cog teeth by .020" and increase the widths of the two adjacent grooves by .010" each to compensate. I've got a 20-tooth cog now with those dimensions and I can get really high speed out of the setup -- the treads just blur. Will upload a new version of the 12-tooth cog and the bogie soon.
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Re: Hardwareless Toy Caterpillar Tread System

Postby insta » Thu Jan 25, 2018 7:22 am

That's really cute :mrgreen:
Custom 3D printing for you or your business -- quote [at] pingring.org
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Re: Hardwareless Toy Caterpillar Tread System

Postby EricPeterson » Thu Jan 25, 2018 4:32 pm

Thank you sir!

Here's the 20 tooth drive cog with the revised clearances -- only one side for now. Remember these are right- or left-handed cosmetically because the track is asymmetric on the back:

http://www.scifiwheels.com/images/M2Parts/cog20t.zip

Here's a short fuzzy ancient cell phone video -- the phone is ancient, not the video -- of the 20t cog running free with the 2.82" pitch diameter bogie.

http://www.scifiwheels.com/images/M2Par ... 20TCog.wmv
EricPeterson
 
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Re: Hardwareless Toy Caterpillar Tread System

Postby EricPeterson » Thu Jan 25, 2018 4:52 pm

OK, the 20 tooth drive cog link gets you both right and left versions now. Again, the only difference is which side has the build platform added, so that you get a nice surface finish on the side with the grooves you need for the track on that side of the vehicle.
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