New Track Idea

[Joshua Updyke]

Hello all,

My name is Josh and I am a robotics engineer. I do a lot of medical robotics during the day and mess around with RC stuff for fun. I was thinking about building a RC lawn mower because I figured it would be more fun to build the robot then mow my lawn. Plus sitting in the shade with a beer while I drive a RC lawn mower around the yard sounds great. Anyway, stumbled onto this group when looking at the track options. This page was really helpful http://www.rctankcombat.com/articles/track-systems/ and I got an idea that I wanted to see what people thought of it.

I really liked the chain and bolt track idea. Using standard roller chain has a lot of advantages. Lots of sizes, strong, standard drive parts. But I did not like how all the load was on the chain and not the middle tread. Seems like you might not get much grip in some situations. So I started toying around with the idea of a custom tread, that you mounted to the roller chain. You could have various sizes, for different chain. Maybe even have different tread profiles to pick from. I 3d printed some parts to make prototypes and I ordered the materials to cast about 50-100 parts. I figured I would see what you guys thought. Maybe pick your brains. The final part would probably be injection molded. I do this kind of stuff at work so I have some contacts.

Any comments welcome. The red ones match #35 chain and are 3" wide, the black match #40 chain and are 4" wide, and the white match #50 chain and are 5" wide. Maybe I am just missing something obvious since I have never build a tracked vehicle.

[Jean-Maxime Cyr St-Pierre]

Probably some experienced guys would say that too much grip mean difficulties to turn neutral on grass and drawn to much amp. to your motors.

In second I would say that some guides thooths would probably work better even if it's seemmed to work. Your super traction will probably trow off your track at the first turn...

I'm not experienced a lot but i got a 80% tank hull that will maybe running this weeckend, but a lot of guys reduce their grip with flat tracks even let some screws heads out to run better on all

conditions..

Out of that good work and make lots of testing cause tracks are cool but hard to master!!!


Jean-Maxime Cyr St-Pierre

---

Date: Fri, 6 Feb 2015 12:00:56 -0800
From: jup...@gmail.com
To: rctank...@googlegroups.com
Subject: [TANKS] New Track Idea

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[Derek Engelhaupt]

It is true that too much grip is a bad thing.  There is a balance in the middle somewhere.  Since the tracks you are making are based off of the idea I actually built and used on one of my tanks I can lend some insight into them.  The pics in the article are of my Sturmtiger.  My original thoughts for the tracks were very similar to yours (ie: using blocks like that between the chains).  I didn't do it for simplicity sake and cost.  I was trying to make my tracks on the cheap.  I have since changed to stiffer steel 60 pitch tabletop chain tracks (Rexnord 1864K4.5 http://www.rexnord.com/rexnord_web_media_prod/pdfs/1864%20Series%20TableTop%20Chain%20Product%20Portfolio.pdf ). I did this to minimize the side to side flexing of my original design you have modified.  The design you are using may work for your application, but there are some things to take into consideration.  The problems I had with the tracks was keeping them on the sprockets.  I was using a free wheeling set of toothed sprocket on the front and a set of toothed drive sprockets on the rear.  With enough tension, the tracks will stay on the sprockets well enough.  My issue was that tension.  The more tension I put on them, the more drive line losses I got (ie: the motors had to work too hard).  I also had a full suspension on my tank.  As the tension increases it would compress my suspension and therefore cause it not to work as intended.  With a fixed suspension, that issue would go away.  I'm assuming since it's a mower that it won't have a suspension on it.  You will at a bare minimum want to add guide teeth to your tracks to keep the tracks running straight through your road wheels and make sure the tracks stay under the wheels.  Without guide teeth, your tracks could run out from under the road wheels doing neutral turns.  You could also add outer guides to the drive and idler sprockets at the front and rear of the mower to aid in keeping the tracks on the sprockets.  If I were doing what you are doing, that's what I would do so I could keep the track tension on the looser side to accommodate sucking up rocks or twigs into the tracks.

I haven't abandoned my track idea, but the prefab Rexnord tracks were about $100 when I found them on Ebay.  Kinda got lucky I think with those.  That $100 was well spent saving me time and frustration of building my own.  I may revisit my idea and fix the issues with it one day, but I haven't really had much time to devote to tanks in the last year or so.

Derek

T065

SV016

[Joshua Updyke]

Thanks for the comments. I am by no means an expert in track design. But I did a little homework. I know there are lots of styles of track out there and I am trying to learn as much as I can about them.

The grouser style is the most common and simple. It has a lot of grip and great for muddy surfaces. But it tears up the ground and has a hard time turning.

Then you have skid pads. They are better with turning and can work on hard and soft surfaces. Notice the taper on the sides of he tread profile. This helps with the turning. I made sure the tread design I was looking at had a decent taper to help with turning. 

Then you got V track like this one. From what I understand these are good in mud and snow. They push the wet material through the track and to the sides. So it get is out from under the tracks. A nice feature, but I wanted a more generic track system. So I avoided this style.

So that is some of the design considerations I looked at when picking a tread profile. I really would like to learn more about tread profile design and selection. I also would like to learn more about track systems in general. 

Here is a really cool video that shows the difference between having a good suspension and not. 

https://www.youtube.com/watch?v=wUsyMDvPW6U

 

[Derek Engelhaupt]

Suspension does complicate the track making process.  If you could design a variable tension device for you tracks, that might help things too or it could just make things worse... lol

Derek

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[Joshua Updyke]

One of the aspects about using roller chain allows all the stock roller chain parts to be used. Roller chain is quite common and parts are pretty cheap and easily available. I was thinking of using several chain tensioners like this one.

[Doug Conn]

I’ve been working on something very similar, but I went the attachment chain route. It can still be driven with standard sprockets, but it’s more expensive and harder to get than roller chain. To attach your grousers to the roller chain, do you need to disassemble the chain ?

 

I’ve been working in two different sizes. There’s a rubber strip that covers the bottom. Here are the prototypes:

 

    

 

I resin cast a full set of the larger tracks and put them on my tank, Bad Kitty. It’s been through a few battles with them now, and they’ve performed great. I can go over terrain where other tanks simply cannot and I believe it’s due to the tracks in large part. I need to keep the tension a little higher than I’d planned, but there are no track-throwing problems.

 

   

 

Steven Morgret, an R/C Warship aficionado and entrepreneur known to a lot the R/C tank group, injection molded me a set of the smaller tracks. A photo is below. He just mailed them yesterday and I can’t wait to see them in person. It looks like he did a really outstanding job !

 

 

Here’s the new tank I’ll test them on. The hull is mechanically finished. I just need to wire it, add tracks, and try everything out.

 

  

   

 

-          Doug

[Joshua Updyke]

Doug,

That is just fantastic. I thought about the attachment chain route and decided if I could make it work with standard roller chain it would be the better way to go. I also thought about a two part tread. The base and insert. That would allow me to make different inserts and people could use them in different ways. I have been working with several injection molding companies. The one I am planning on working with is willing to overmold my tread around some threaded studs. The studs would add rigidity when the rest of the part is rubber. I also talked with them about creating the mold in such a way that only the top part of the mold would need to change to make a different tread profile. 

My design does require you to disassemble the roller chain which is a huge pain in the butt. lol. However, that is not my plan past the prototype stage. I have talked to a few roller chain companies about selling me assembled chain without the pins. Then you just assemble the parts as a kit. They seem willing provided I need more then a handful of parts. Worst case, I have a plan for a machine that would feed roller chain in and it would push out the pin with a pneumatic cylinder. I could automate the process. But I really think getting the chain parts will not be a problem.

What size chain is that? I am curious what widths people are using. I tried to keep my design modular and scalable. I did all the 3d modeling with parameters. So you can pick the size chain and the width you want. I have prototypes for #35, #40, and #50 chain. The widths are currently 3", 4" and 5" respectively. 

Josh

[TyngTech]

Doug,

The new tank looks impressive.  Can't wait to see it on the battle field.

ST

[TyngTech]

Josh,

Impressive work so far.  It looks like your modeling your tracks after construction equipment.  This is fine for low speeds, flat surfaces and no suspension.  I think you will find these tracks will throw quite often in our typical battling environments and speeds.  If your after a performance track, you WILL need to incorporate guide horns IMO, especially if your thinking suspension.  Also, other traits that make for a good performance track IMO are stiffness along it's length, light weight, and ability to shed debris.  It doesn't take much to distort a track to the point where it will disengage from the drive sprocket.  The finer the sprocket mechanism the more so in my observations.

Steve Tyng

[srwh...@gmail.com]

Doug looks awesome. The tacks look great.
Once i get my suspenion together (finally figured out) i will seriously start racking my brain for track. The goal tank is a AMX13 .

Stewart

[Frank Pittelli]

Looks like a sweet ride Doug.

There's one important aspect about your track design that you failed to
mention: the rigidity of the 90 degree angle between the chain and the
tread. If that angle is not held rigid over the life of the track, the
probability of throwing a track goes up. Attachment links significantly
increase the rigidity and therefore the reliability of the track.
Personally, I think that your attachment chain design is as good as a
chain-based design can get. End of evolution.

The performance of the TTS design is legendary and well-proven on the
battlefield (which makes all other R/C tests look like kindergarten
projects). Will's and Doug's attachment chain designs are also
seasoned. Not as good as TTS, but definitely battlefield approved.
Basically, the last category in track designs that hasn't been fully
explored is self-linked treads.

If you're going with 3D printing for prototypes and injection molding
for production, you might as well design an interlocking tread that can
be pinned together just like the real thing. When used with a properly
designed drive cog and guide tooth, you would never throw a track.
Moreover, a cleverly designed set of parts could be used to make a wide
array of different tracks. Single-tooth, double-tooth, offset tooth,
narrow, medium and wide tracks could all be built using the same
elemental parts. If you combine the pioneering work done by Garnet for
T011 with 3D printing and modern injection molding, I think the result
could be successfully battle-tested and used on a wide-variety of vehicles.

Loic and FoA have pushed that frontier further along with their scale
metal track links, but I don't think the evolution is done and a
semi-scale version in plastic would be greatly appreciated in many
different R/C worlds.

[Joshua Updyke]

Steve,

Thanks for the input. My goal is to create a generic track system that can be used on tracked robotic projects, tanks, and other RC vehicles. What I liked about using the roller chain was I could have various sizes that all functioned the same way. You mentioned guide horns. Can you post some picture of what you are talking about. I did a few designs that had a feature on the bottom to guide some sort of boggie wheel. But I was not sure what would make a good boggie wheel. One aspect of this project is that I like the availability of roller chain sprockets and and parts. If I was going to design a guide horn for a boggie wheel into the treads I would like them to match another widely available part. 

Another thought I had was that my current design the tread covers the roller chain to prevent things from getting into the chain. That might not be the best method because it does not allow things to get pushed out either. I also thought about only putting half the chain on and leaving the one side open. But I didn't know how that would work out.

Josh

[Joshua Updyke]

Frank,

Thank you for your comments. You really have a lot of good ideas. You mention the TTS design. I am not familiar with that and I was wondering if you could point me in the direction of some reading on that. I also liked your suggestion of just making a well designed interlocking tread from the beginning. The reason I liked using the roller chain is it added strength to the track and allowed me to use very common drive sprockets. One idea I toyed around with was removing the chain and building a pinned tread that still meshed with roller chain sprockets. Do you think this is practical? You mentioned a 'properly designed drive cog' in your post. I realize that a roller chain sprocket is not designed for driving track, but what differences are there between a roller chain sprocket and a drive cog. 

Thanks for the input from everyone.

josh

[srwh...@gmail.com]

Joshua, go to the groups home page and there is a section of "How To articles". You will find a section on tracks. You will find TTS there. The guide horns are teeth on a tank track system the fit eather between or inside the road wheels. The keep the tank from turn itself off the track (throwing a track) google pics of
tank treads.

Stewart

[srwh...@gmail.com]

Great example of guide teeth here

http://m.123rf.com/photo-21860408_photograph-of-decommissioned-wwii-us-army-tank-stuart-m3a1-caterpillar-drive-mechanism--detail.html

[Jean-Maxime Cyr St-Pierre]

You can go look at the tank part of the web site( http://www.rctankcombat.com/order-of-battle/tanks/  ) and see on how to built the diferent systemes and some update that are not on the how to articles page! Like the TTS with drive cog like the T040 , T077/79 and T081 that are totally diferent but not standardised.

Jean-Maxime Cyr St-Pierre

> Date: Sun, 8 Feb 2015 06:52:46 -0800
> From: srwh...@gmail.com
> To: rctank...@googlegroups.com
> Subject: Re: [TANKS] New Track Idea

>
> Joshua, go to the groups home page and there is a section of "How To articles". You will find a section on tracks. You will find TTS there. The guide horns are teeth on a tank track system the fit eather between or inside the road wheels. The keep the tank from turn itself off the track (throwing a track) google pics of
> tank treads.
>
> Stewart
>

[TyngTech]

Josh,

A TTS track (short for Tyng Track System) uses a continuous loop of treadmill or conveyor  belting as the main tension member.  The "tracks" are mating pads adhered to the inner and outer faces of the belt.  Guide horns are incorporated on the inner pads.  Guide horns engage the roads wheels to limit  side to side play.

First TTS being fabricated for T005 (friction drive): http://www.rctankcombat.com/order-of-battle/tanks/T005/Page4.html

First sprocket driven TTS on T028 (converted from friction to sprocket): http://www.rctankcombat.com/order-of-battle/tanks/T028/

First production TTS T040: http://www.rctankcombat.com/order-of-battle/tanks/T040/Page3.html

Current polymer TTS from TriPact:  http://www.rctankcombat.com/order-of-battle/tanks/T100/Page2.html

There are other TTS implementations, just look through the build threads.

Steve Tyng

[Joshua Updyke]

First off I want to thank everyone for the help in the design so far. The feedback has been great and being able to get answers to some questions has really pushed my design forward. I have done some redesign and was curious about peoples thoughts. I looked through the various links and that gave me some inspiration. So this new design is still similar and still uses standard roller chain. There is a tread that is molded over two pins. These pins replace the pins that are pressed into roller chain. I have talked with a roller chain manufacturer and they said they would be willing to sell me assembled chain parts if I got them in large enough quantities. 

I also designed a replacement roller chain plate that has the horn feature built into it. What I really like about this is it becomes an option. If you want horns you put the horned plate on, if you dont you use a standard roller chain plate. That also lets me make changes to the horned plate without scrapping the whole design. I had a few questions about the horns. These links are 3" wide, about how tall should the horn protrude? What width between the horns would be best? and what angle should the horn have to push the boogie back in place. Anyone have thoughts on those questions.

I was also planning on using a threaded rod and nylock nuts to hold the chain on. This would work okay, but finding a standard bolt that matches the roller chain is tough. For #35 a 6-32 fits really well. But other sizes don't fit as well. So I got the idea from FOA to use a headless pin and snap rings. But when you start looking at snap rings the common sizes dont match up very well. I have a few quotes out to snap ring manufactures to see if they have an of the shelf size that matches better then what I can find quickly. But then it hit me. Master Links for chain have this snap ring already and it is designed to hold chain together. So I am gonna call my roller chain person tomorrow and talk with him about being able to buy only the snap ring part of the master links. If they will sell me the chain unassembled, I don't see why they would not sell me the snap ring too. 

I am going to 3d print some of the horned link plates tomorrow at work and put them on my models just for testing. I will post photos then. Attached are some pictures from the CAD package, a few quick renderings and a short video of the assembly process.

[Joshua Updyke]

Well it seems I cant upload a video here. Or at least I don't know how. So here is a link to the youtube version. It didn't load correctly for me the first time I watched it, but if I hit replay it worked fine. It is only 7 seconds long, so watching it twice is not a big deal. :)

https://www.youtube.com/watch?v=avdna7Y5KMU

[srwh...@gmail.com]

Just want to mention some tracks have the horn (teeth) in pairs or a single horn in the centre. The dual horns have the tank road wheel roll between them. The single centred one go through the centre of a double road wheel (think oreo cookie on its side). Many modern armour vehicles use this type.

Stewart

[Joshua Updyke]

Stewart,

Do you know one method is preferred over another? Or if one has advantages or disadvantages? 

I saw that some were on the outside and some are inside. With my design it is not too difficult to put it on the outside. I was trying to think of a way to put it on the inside as well. I was laying in bed thinking about ways to make the track modular and let the end user decide. For example if the track had a split in the middle and could be assembled in different ways. No horns, middle horn, side horns, or even both middle and side if you wanted. Not sure if you would ever want that.

Josh

[Frank Pittelli]

Why do you include roller links in the design? Or, in other words, what
problems do they solve?

Wouldn't it be cheaper and easier to have two pins embedded in each
tread as you show in your design and then mold a link that connects two
treads together. The link could then be shaped to fit into a molded
drive sprocket. You could incorporate as many links as you need along
the length of each tread to ensure reliability. Furthermore, one or
more of the links could be shaped as guide horns to suit whatever guide
horn arrangement is needed for the vehicle (2 horns/1 wheel vs. 1
wheel/2 horns, etc)

[Joshua Updyke]

Frank,

Well the reason I am looking into using roller chain is to allow it to match up with all the standard roller chain sprockets. I would be able to get any standard roller chain sprocket, tensioner or other product designed for roller chain cheaply and easily. You could use the roller chain calculators to determine correct sprocket spacing. Another key reason is that roller chain is mass produced which means that those parts are widely available and cheap. Up to this design the only custom part was the tread. So rather then getting several parts custom made I would only need to get one custom made. 

The new horn plate is now a new custom part. But the geometry is fairly simple. I would only be a single part mold. If I can use two of those parts back to back to create a center horn, then I could use the same mold. 

I am looking at being able to make these in small batches myself, but mostly at trying to make them in bulk and sell to hobbyists. I know that you guys are focused on tank replicas and I would like the track to match those goals. But I am hoping that robotic hobbyists could also benefit from this design. So building tanks, tracked robots, RC lawn mowers, bomb disposal robots, and hopefully more.

That is a little bit about my thought process that got me to this point. 

[Frank Pittelli]

All the more reason to make everything from molded plastic as much as
possible and, more importantly, to use a design where a small number of
parts (say 4) can be used to build a variety of different track widths
and configurations. With a slight modification of Garnet's T011 design,
such a goal is achievable. If you develop the following parts:

- 1 inch long pad
- 1.5 inch long pad
- simple link
- horned link

they can be combined to build virtually any tank track configuration
used during the last 100 years and could also be used to develop tracks
for a wide array of robots. Design a plastic sprocket to mate up with
the links and it's a complete system. Best of all, assembly and repair
would only require inserting and removing straight pins that either
press it into the links or that have slip rings on the ends. In either
case, such pins are stock items.

And, from a business standpoint, you maximize revenue by producing all
the parts yourself. Modular, all-in-one solutions are the goal of all
product companies because that's what the market always wants.

[dwco...@comcast.net]

One thing I learned about injection molding is that you can't mold a part with a long hole through it. Even a 1" long hole would need a substantial cone shape to it to provide enough draft to release the part form the mold. It makes sense when you think about how the mold works and the parts are produced. You can use a 'sliding shutoff' technique, but that would produce a part with a lot less strength right where a track link needs it - along the joining pin.

 

  - Doug

---

From: dwco...@comcast.net
To: "rctankcombat" <rctank...@googlegroups.com>
Sent: Tuesday, February 10, 2015 3:34:15 PM

Subject: Re: [TANKS] New Track Idea

One thing I learned about injection molding is that you can't mold a part with a long hole through it. Even a 1" long hole would need a substantial cone shape to it to provide enough draft to release the part form the mold. It makes sense when you think about how the mold works and the parts are produced. You can use a 'sliding shutoff' technique, but that would produce a part with a lot less strength right where a track link needs it - along the joining pin.

 

  - Doug

---

From: "Frank Pittelli" <frank.p...@gmail.com>
To: "rctankcombat" <rctank...@googlegroups.com>
Sent: Tuesday, February 10, 2015 1:59:41 PM

Subject: Re: [TANKS] New Track Idea

[Joshua Updyke]

Doug,

Thanks for the advise about the injection molding. I agree that a long through hole is a pain but possible if you design around it. That is one of the reasons I liked the overmolding design. You do not have to worry that problem. It also makes a much cheaper mold. I am hoping to use of the shelf pins with grooves for snap rings. But one that fits is a little tricky. That is one of the draw backs of using the roller chain is I need pins that match the rollers. If I designed my own connecting link it would open up the ability to design around a pin. But that would mean custom links, and custom sprockets to drive it. I would prefer to avoid that. If the trade off is designing and fabricating the pins, or the link / sprocket I would pick the pin. They are very simple parts. Also, the quanties that I am thinking about are around 15,000 treads. So that would be 30,000 pins. In that quantities I can't imagine not being able to get the pins as cheap as any of the shelf product I could find.

I know that this sounds quite high quantities. I could do less, but the price per part goes up then. 15,000 treads is only 625 feet of track. Or about 300 kits of 2 foot tracks. 

Anyway, hopefully my works 3d printer is not busy the next few days. I want to print some test parts and do a pilot run of molded parts in rubber. Plastic tracks just don't feel quite right.

Josh

[Frank Pittelli]

"2 foot tracks" ... any vehicle with only a 1 foot wheelbase is not
worthy of a track :=)

Real tanks and robots have 2-3 foot wheelbases or roughly 6 foot tracks.

[Joshua Updyke]

Frank,

I agree. I was just thinking 50 links kits. If you want two or three kits to make your robot then that works as well. If I can pull this thing off I will pre-sell kits such that I break even with the mold cost. I don't make any money on those kits, but now I own the injection mold. After that I can sell the links online and just let people pick how many they want. Or maybe offer them in increments of 10 links or something. I am hoping to make a product that will let me build tracked vehicles for fun, and help other people do the same. If it funds my other hobbies that would be great too.

Josh

[srwh...@gmail.com]

Joshua,
Modern MBT seem to have a sigle horn with split road wheels for better weight coverage over the tracks compared to older tanks. My current plan is a light tank which uses track with two horns. Also small lighter tracked vehicles seem to still use a single road wheel and double horn type track. You would need a notch in the centre to take a horn and i guess a hole ffrom side to side for a pin to hold it.

Stewart

[Odyssey...@aol.com]

sorry i didn't comment sooner, as i'm now limited with my on-line time until i get a new tower built (mine finally toasted a few weeks ago).

 

what are you planing to use as guides on your tracks? why not do something similar i did with mine? i have my guides being used in place of nuts. the bolts pass through from the bottom of the link, through the attachment tab and screw into the guide. you could to the opposite, you could have the bolts pass down through the guide, through the tab and thread into the link itself.

 

as for Josh, maybe you could do something similar and screw your guides to the tracks going through the bottom of the link. this way if a guide ever where to break, just bold on a new one 

 

chris

 

how do the rubber pads hold up so far? i take it they are held in place with contact cement?

 

i take it

 

In a message dated 2/6/2015 11:14:29 P.M. Eastern Standard Time, dwco...@comcast.net writes:

I’ve been working on something very similar, but I went the attachment chain route. It can still be driven with standard sprockets, but it’s more expensive and harder to get than roller chain. To attach your grousers to the roller chain, do you need to disassemble the chain ?

 

I’ve been working in two different sizes. There’s a rubber strip that covers the bottom. Here are the prototypes:

 

    

 

I resin cast a full set of the larger tracks and put them on my tank, Bad Kitty. It’s been through a few battles with them now, and they’ve performed great. I can go over terrain where other tanks simply cannot and I believe it’s due to the tracks in large part. I need to keep the tension a little higher than I’d planned, but there are no track-throwing problems.

 

   

 

Steven Morgret, an R/C Warship aficionado and entrepreneur known to a lot the R/C tank group, injection molded me a set of the smaller tracks. A photo is below. He just mailed them yesterday and I can’t wait to see them in person. It looks like he did a really outstanding job !

 

 

Here’s the new tank I’ll test them on. The hull is mechanically finished. I just need to wire it, add tracks, and try everything out.

-          Doug

[Joshua Updyke]

Okay guys here are some pictures of Revision 4 of my design. I 3d printed some horns to add to my previous revision 3. The pictures show both inside and outside horns. This is to show both ideas. But I don't imagine anyone would want both horns at the same time. I am pretty happy with the outside horn design. This would be another custom part, but the design is really simple and a one part mold. So I could cast these at home in a silicon mold pretty easily. The inner horn option still needs some work. Right now it is glued on and my original idea was for it to attach with a screw through the middle of the tread. But After testing that out it will not be as easy as I thought. I think I need to add some interlocking geometry in the center of the tread to help with this. Also I think the center horns are way too wide. But I am curious about your thoughts.

My questions are these:

Can anyone provide details about the horn geometry? Both in real tanks and in the 1/6 scale versions. The angle along the length of the track is related to the tightest bend of the track. But I am unsure of the other angle along the width of the track. This would be the angle that the bogie wheel would try to climb when turning. 

How strong do the horns need to be? If they were made from a hard plastic like ABS would that work? Legos are ABS if you need a good idea of the strength of ABS.

[neroc1]

 This is just my personal opinion but Id choose a much steeper side angle than what you have printed. I dont think there will be an advantage having any more that 5 degree off the horizontal . Why do you want to use 3 guide teeth ? 

[Joshua Updyke]

Thanks for your comment about the 5° angle. The ones I have now are 22.5°, but those were just me picking a starting point. If you read my previous post I mention that I am not planning on using 3 guide teeth / horns. I am just showing both center horns and side horns at the same time. You would pick one or the other when assembling the track. I am planning on getting the tracks injection molded, so I want the design to be modular. It is easier to change the design now before the mold is machined.

Josh

[Frank Pittelli]

You can't go wrong with either of the horn designs shown in the attached
photo. Both have been used on battle-tested tracks for a number of years.

The simple clipped pyramid design of the horns in the background have
the following dimensions:

Base Width = 1/2"
Top Width = 1/4"
Height = 3/8"

The more complex clipped pyramid design of the horn in the foreground
has the following dimensions:

Base Width = 1/2"
Mid Width = 7/16"
Mid Height = 3/8"
Top Width = 1/4"
Top Height = 1/2"

The almost vertical angle on the bottom of the horn keeps the road
wheels from riding up the horn. (NOTE: It can't be exactly vertical,
because that would make it harder to extract from the mold.) The steeper
angle at the top of the horn helps with alignment as the horn meets up
with a road wheel or drive sprocket.

Because of their dimensions, these horns are very strong, regardless of
the material used, with plenty of surface area at the base for attaching
to the treads. In the treads shown, the horns are molded as part of the
treads, without any reinforcement.

With regards to materials, I personally wouldn't use ABS because it
tends to be a little brittle, especially in colder conditions. A more
durable plastic, like polyurethane or polyethylene, would be best.
Durability, not strength, is the key mechanical property to be considered.

[SAGE WISDOM ON]

Your latest design revision is still more expensive and requires no less
assembly than a molded set of interlocking parts that are pinned
together. So, I'll repeat the prime design question: What problems are
being solved by the use of the roller chain and are those results worth
the added cost and design/performance constraints imposed by the roller
chain?

You can't ignore the fact that the potential track buying market will
want a wide variety of different track configurations, with the two most
important variables being track width and horn placement. The best
design, therefore, would use the fewest number of interchangeable parts
to yield the largest number of different track configurations. Your
current design yields at best four different track configurations (no
horns, middle horn, one side horn, two side horns), all of which are the
same width.

The whole purpose of CAD-based, 3D prototyping is to explore a vast
array of options before committing major resources to a product. Have
you explored all approaches?

[SAGE WISDOM OFF]

On 2/15/2015 8:48 PM, Joshua Updyke wrote:
> Can anyone provide details about the horn geometry?

[Joshua Updyke]

Frank,

Thank you for the details about the horn design. That is exactly what I was looking for. I really do appreciate your help despite it seeming like it is falling on deaf ears I truly am taking your wisdom into account. Also, thank you for the suggestion about the plastic to use. Now that I think what you said it makes sense. I finally got some new resin and parts for my Form1 3d printer. All the parts I have show were printed on my Makerbot which is cheaper and faster to use, but less accurate. I currently have some parts printing on the Form1 which I will use as the master for the silicone mold. Then I can test out the over-molding process, and get parts that are in the correct durometer rubber.  I also plan on using the Form1 to make masters for the horns and cast them out of polyurethane. These should be single part molds and easy to make. Fingers crossed.

• This brings up another question I had; I am going to mold them in a Shore A 70 rubber, which is basically the same as car tires. That was my best guess at what would be a good material for things.
  

Why Roller Chain?

I will again restate the reasons for my design decisions. The idea of using roller chain as the foundation of my design gives me a few key aspects which I am fond of. It is a standard design with many off the shelf parts working with it. Most notably the sprockets. Using standard roller chain means that I do not have to make custom sprockets. This might seem like a small thing if you only planned on using one sprocket size. But I really like the idea of using any size sprocket. These sprockets are also already design with many different methods of attaching to shafts. McMaster has about 100 sprockets for #40 roller chains. Diameters range from 1.67" all the way to 15.57". Idlers with built in bearings, machinable bores, finished bore with keyway, nylon, metal, bushing, taper lock and more. In addition to the sprockets, you have tensions, idlers, and the design tools that help you select the perfect spacing of multiple sprockets in a chain system. I am still thinking robotics an not just tanks. 

If I were to design a system that has a molded connecting link this would be an additional part to design and I would have to make custom sprockets too. Like I said before I could design one sprocket, or maybe 10. But then I have the cost of making them, storing all the sizes, tooling costs, and I am never going to have 100 types for each size chain. 

In addition to the sprocket and accessory aspect, roller chain is very durable and has known tensile ratings. This is similar to the metal bands that are placed in the solid rubber tracks found on construction vehicles. The rubber tracks I am getting injection molded are not taking the loads. The chain will take it. I like that aspect as well.  

One final thought about the roller chain links is the cost. Roller chain is $13.92 for 10 foot of #40 chain. #40 chain has a pitch of 0.5", so that means 240 links. That is 5.8 cents per link. I don't think I could get links made that cheap even in quantities of 60,000. Maybe I am wrong. Or maybe I am missing something obvious to you guys that know more about this. But those are the design aspects which made me like this idea of using roller chain. 

You mention the width of the track not being flexible in this design. I agree with that. I have not found a good way of doing that. It is much cheaper to injection mold over a dowel pin then to make a hole. Talking with the injection molding companies I work with, having a hole will make the mold tooling and per part cost go up substantially. I even asked about molding over a metal tube. But that is problematic as well. I think for now I will have to settle for picking a single width for each size chain I want to work with. For now that is #35 chain being 3" width, and #40 chain being 4" width. 

• Do you think you could use an idler sprocket that meshed with the drive chain as bogie wheels? You might not need horns with that design. I have never seen that on tanks. maybe I am missing something obvious?

As always thanks for the comments guys. I have got a lot of great suggestions, information and mostly just some place to talk about tank track. My couple friends are not really very interested in talking about bogie wheels, tread design. They just nod and say yeah that sounds cool.