pic: Omnitrack Summer Project?

[Bill_Hancoc]

I had an idea smiler to this a few weeks ago for a crab drive tank system. It involved 4 little individual triangular tread drives that could pivot on a dolly type system and then would be able to turn parallel to each other. The individual tread drives would be about 6-7 in long on the bottom and be based off a slightly modified 30-60-90 triangle. I wanted it to be fast along with really powerfull via a shifting gearbox but after calculating the speeds needed for a 1.5 in tread pully it would have been very hard to go fast since it would have reuired a really high rpm higher than the small CIM is i remember.

[RogerR]

Originally Posted by Bill_Hancoc

I had an idea smiler to this a few weeks ago for a crab drive tank system. It involved 4 little individual triangular tread drives that could pivot on a dolly type system and then would be able to turn parallel to each other. The individual tread drives would be about 6-7 in long on the bottom and be based off a slightly modified 30-60-90 triangle. I wanted it to be fast along with really powerfull via a shifting gearbox but after calculating the speeds needed for a 1.5 in tread pully it would have been very hard to go fast since it would have reuired a really high rpm higher than the small CIM is i remember.

in 2001 used belts instead of wheels to help them climb the midfield barrier. after a bit of searching, i found a pic here (thanks 229).

based on my calculations, to travel at 15 ft/s with a 1.5" driving pulley, you'd need almost a 2.5:1 gear reduction, which could be done in a single stage.

i think the biggest problem to overcome with your design would be turning the modules themselves; 6-7 in of high friction material would create a pretty good resistive moment.

this design is obviously do-able, there's just a few problems to solve; but then, how much fun would all this be without any problems?

[Simon Strauss]

I'm thinking that this would work better if the 4 treads were positioned like traditional wheels would be and the rollers at either 30deg or 45deg so that it would function just as mecanum wheels but with the advantages of treads.

[Greg Perkins]

Originally Posted by nycpunk

I'm thinking that this would work better if the 4 treads were positioned like traditional wheels would be and the rollers at either 30deg or 45deg so that it would function just as mecanum wheels but with the advantages of treads.

I assume you mean Omni wheels. And no, this won't behave like tank treads, it's a whole different animal. You've got to take into account being pushed, your coefficient of friction, and the need of the design. Is it doable, yes...is it practical, don't know. Do some research, and let us all know please!

[Simon Strauss]

Originally Posted by Greg Perkins

I assume you mean Omni wheels. And no, this won't behave like tank treads, it's a whole different animal. You've got to take into account being pushed, your coefficient of friction, and the need of the design. Is it doable, yes...is it practical, don't know. Do some research, and let us all know please!

No, i think i know what I'm saying as confusing as it may be, let me explain then feel free to correct away(i might want to pursue this idea of mine). It has already been established that this system is going to be implemented in four different treads each at a corner of the robot, my idea is to instead of having the rollers 90deg from the direction of the tread moving as shown in the picture, have them set at either a 45deg or 30deg and leave the treads parallel to the other side. My reasoning for believing that this may work is that if you imagine traditional tank treads as just an elongated and spoke-less wheel that travels in an ellipse to move its load instead of a circle, setting the rollers this way will function as nothing more than this perception applied toThese Mechanum wheels on the first page, with all the drive and other characteristics of the wheels applying to them. If this however is too confusing because my mind works in strange ways the treads will be positioned like
l l
l l
and the rollers positioned like
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just an idea and ill try to make a more detailed drawing to clarify what i mean when i get time
-Simon

[s_forbes]

I thought of omnidirectional treads too when trying to think of an interesting drive system and it's nice to see that someone else is persuing the idea.

One problem I thought of though is this:

If you have 1 tread on each side of the robot, then each tread will only receive about 25% of the total weight of the robot. When you try to push someone forward, you will only be using two of the treads. Since only 50% of your robot weight is on those treads, then you have a significantly reduced pushing power (less traction than a typical 4 wheel robot), even though you are using treads.

Then I remembered "Oh wait, omni treads would be sweet!" and it cancelled out the previous thought.

[Gabe]

Originally Posted by s_forbes

If you have 1 tread on each side of the robot, then each tread will only receive about 25% of the total weight of the robot. When you try to push someone forward, you will only be using two of the treads. Since only 50% of your robot weight is on those treads, then you have a significantly reduced pushing power (less traction than a typical 4 wheel robot), even though you are using treads.

True enough, and I have given much thought to different drive configurations.................................... ......................................... My favorite (4 treads):....Another idea (3 treads):...........Killough (3 treads):

== == ==.||....................||.............||........ ......................== == ==
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||...........||....................||............| |................................\\.......//
||== == ==................................................ .........................\\..//

Realistically, these will take time and money to make, so I am thinking about this for a test platform (2 treads, 2 omniwheels working in tandem):

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||< >||
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To have the best performance on the field, you would have each tread independently controlled. Just to throw another idea onto the field, what if you used four DeWalt 3-speed shifters with FP motors, and had a 3-speed omnitrack robot? That would be incredible.

Why consider omnitreads at all? Two words: Freaky Mobility.

I am having problems attaching images. Periods represent blank spaces. Sorry.

[Tatsu]

With all honesty, this is cool, but it makes no sense to me.

You should put the wheels in a diamond pattern, so when you're pushing forward, you're at around 75 not 50% efficiency.

But what makes no sense, is why you want treads.
For non-deforming surfaces, frictional force is independent of area. IIRC, Tank treads make sense in that they can "dig in" and create normal force (instead of frictional force) but these AM rollers dont deform, dont dig in, dont really do anything but add weight. since there's only two points where the weight is supported (the aluminum sprockets) this is functionally equivalent to having two omnis on each side of the square.

Also, why are you filing? you have access to a SWEET cnc mill, it'd only require a fraction of the machining you did for your wheels

Tatsu out.

[Dillon Compton]

Uhm...If the rollers are at 45 degree angles to the tread, then the tread should be mounted parallel to the frame at the four corners; the nature of mecanum systems is such that you receive standard weight distro, speed, and forward traction, while gaining the manuverability of omniwheel systems.

Good luck.

[Tatsu]

I dont the the OP is talking about 45 deg rollers, and if OP did do that, he'd need the treads set up like traditional mecanum wheels (ie two treads / side) rather than the square shape he has now.

[Chuck Glick]

im just wondering how the work on this idea has been going along, because a couple of members on 1712 along with myself are working on a omni tread design as well. just wondering how far its gotten. and i think i figured a way to keep the treads in a straight line and have a good sprocket for them to move on.

[Gabe]

Originally Posted by SirCharles982

im just wondering how the work on this idea has been going along, because a couple of members on 1712 along with myself are working on a omni tread design as well. just wondering how far its gotten. and i think i figured a way to keep the treads in a straight line and have a good sprocket for them to move on.

Not so well, because I realized that the tracks would weigh a lot if they were made of aluminum and if each had a 3/16" steel link pin. Also (heh) I noticed that with my design it is physically impossible to install the last link, and therefore it is impossible to complete one entire track. To put the 1/8" steel pin in, it would mean that it would have to go through the 3/16" pin.
If I were to change my design, I would make the links out of plastic, and have cylindrical rollers instead of barrel shaped rollers.

This will give you an idea of what I mean. Sorry about the image, but without AutoCAD, Inventor, or Solidworks, I have to work with what I have: Microsoft Word. This shows the top view of my idea, and you can see the cylindrical rollers with a pin going through (maybe 1/8"). The tread links are joined at the top and bottom by another pin ( maybe 1/8").

[Gabe]

You all have gone through my same thought process. I will address every point, since you all understand what the idea is:

The links are made from 2 different C-channels and each riveted with two 1/8" aluminum pop rivets. The problem is that this is very weak and time-consuming. I have not considered screws, and I will try it. What size: 4-40 or 6-32? Nylon insert locknuts, or tapped holes?

To drive the tracks I am hand filing 2 drive sprockets out of 1/8" aluminum sheet, distanced apart using standoffs. This sprocket engages the ends of the 3/16" steel pins.

I was thinking about the standard attachment chain, but its would be much heavier if I used 2 chains. However, I might scrounge around and find some other material that would work for small rollers traction rollers to be used on just one chain.

Many people have suggested using waterjets or CNC mills. Why does a waterjet or CNC mill seem right for this project? Do you fabricate a bar with the correct profile, or do you cut individual links?

I do have a mill: my 14" Nicholson mill file. Ha, ha! Yes, do file my own #25 and #35 sprockets out of aluminum, and yes, i Am CrAzY. No need to buy those IFI sprockets!

Sorry about that. Just a random fit of insanity.

[Cody Carey]

Why not CNC punch them out? I am fairly certain that you can
punch 1/4 aluminum, and it would be alot more consistant/pretty.

Also... Why omnitracks? Won't a 4-6 wheel omnidrive perform just as well as a two track two wheel design?

[Tristan Lall]

Extrusion requires a difficult setup and expensive tooling; it's only cheap in huge volumes. But what about graphite permanent mould casting? If you can get a local casting shop to sponsor you, it wouldn't take much to make a few hundred links.

Basically, you'd need to mill out the mould into two graphite halves with sprues, vents and risers as necessary (usually CNC—a casting shop will be able to do this easily), and it's just a matter of mounting it to a standard fixture (which opens and closes the halves) before you're ready to pour metal (e.g. 390 aluminum).