pic: LEGO Coaxial Swerve Module
 

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I love it, espcially the turntable to turn the module! LEGO swerves are cool.
I recommend tetrix (?) chain. Using gears to do it would be awkward looking IMO.

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I have worked a lot with LEGO technic construction, even tried my hand at this a couple of times. 24t gears between turntables was promising. You will be putting way to much stress on chains. The key for all of this is to support the gears as best as possible. Your module is nice and compact. The only recommendation I would have is replace the 3-long axel on that 12t with something to run the full length between the two 3x5 liftarms. This will keep the 12t from skipping with the 20t, attached to the wheel, as well as prevent the driving gear from falling off its axel.

Re: pic: LEGO Coaxial Swerve Module
 

How much does it weigh?

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I think you got carried away with the pocketing.

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Ok, this is pretty cool. Thank you for posting it.

What supports the drive shaft? Is there something to limit upward travel of the drive gear? The rest of your design is easier to see in this render.

Re: pic: LEGO Coaxial Swerve Module
 

Thanks for all of your helpful replies!

I have a question of my own regarding the TETRIX chain as I have never worked with it. Is it compatible using the LEGO gears as sprockets? I have a good amount of LEGO chain, but it tends to fail quite easily.

If I can't use chain, I have a design that connects all of the modules together with 40 tooth gears. It seems to work well, but I haven't tested it with all four modules because I only have one module until my order of parts arrives.

In the image, some parts are a bit hard to see from this angle, so I can clarify them. The reason the 12 tooth gear is on a 3m axle is because if I extend it across between the liftarms, it rubs on the tire. The way it is now is the best solution I could come up with. And yes, the vertical drive shaft is supported by the black piece that you can barely see right below the turntable. The drive gear cannot move upward because of it.

As for weight, the module weighs about an eighth of a pound, probably one of the lightests swerve designs ever. ;)

I might be able to get a another render at a different angle so that the underside of the turntable can be seen better.

Re: pic: LEGO Coaxial Swerve Module
 

Asking the real questions here.

This is a really cool adaption to a complex concept, well done!

Re: pic: LEGO Coaxial Swerve Module
 

We're looking at working on some swerve this summer and we might have to build this to play around with control concepts. Awesome job.

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This is definitely cool, but I think in order to survive the obstacles from (e.g.) my childhood bedroom you'll probably want 3 pods rather than 4, and maybe some bigger wheels :D

LEGOs + one of those electric race car tracks (even the simple figure 8) FTW.

Re: pic: LEGO Coaxial Swerve Module
 

Did you try it physically? I didn't have issues with a long axel.

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Definitely want the axle for the idler gear to go across, otherwise it will shake loose / skip teeth / add friction. If you have clearance issues, a different wheel could be used. Lego parts 3482 (wheel) and 3483 (tire) clear the axle with that gear spacing.

More wheels: http://isodomos.com/Visual-Parts-Helper/Lego-Wheel.html

Here's a tiny LEGO swerve drive I made ages ago, using the differential gear piece as the swerve body and bearing. It drove around fine, but in the end they're still tiny plastic parts and can't handle a lot of load.

http://www.chiefdelphi.com/media/photos/28935
http://www.chiefdelphi.com/media/photos/28936

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I haven't tried one of these in years, perhaps it would be worth another go.

Perhaps try using the 4-knob gears? They keep a strong connection if you brace them well enough, though you won't get the same ratio, of course.

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The tires I am using must be a bit bigger than the the tires in the render because I had problems fitting an axle in. While I wish I had smaller tires, the ones I have will probably have to do. Thanks for your help anyway.

Here's a render of the bottom of the module for those who want to see it:

Re: pic: LEGO Coaxial Swerve Module
 

Chain is definitely not impossible. If you are going to go the chain route I would probably put a reduction in the modules themselves in order to take stress of the chain. Personally I would just go with gears, and I would certainly run the center axle through the whole module, as others have suggested. Particularly with the 1/2 stud offset, you are going to be slipping gears extremely easily.

To the OP: Search for "synchro drive" in the website I linked and you'll find tons of examples by people who have done very similar things for years now. :)

And because you are going crab, as an extra challenge, make it drive and steer with one motor total (doesn't have to be at the same time). Yes, it is possible.

Re: pic: LEGO Coaxial Swerve Module
 

This is cool and so elegantly compact. The one Steve made is cool too.

The 12-tooth gear may end up adequately constrained (for the forces involved) by the gear below it and the one above it, laying horizontally. Those 3x5 L-shaped liftarms are pretty stiff so the gears might not skip.

Did you want to use the chain or 40-tooth gears for turning the modules, for powering the drive wheels or for both? Have you considered using long axles and the knob-gears Calvin referred to? The axles aren't that great at resisting torque but then you get gear lash with a large number of gears.

For "Smart Move", one of the local whizz kids and his partner attempted to build a second robot with swerve/crab drive for the Championship in February, after the Qualfier in November. I think their school ran out of parts and they could not manage to get the software going (no mentors on his FLL team). They did end up winning Third Place in Robot Performance using a robot they started building less than 24 hours before the Championship.

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The ones in the render look like tire 89201 with (I am assuming) hub 55982. If you want to acquire some, you can find both easily on Bricklink for cheap. If you haven't used Bricklink before and have questions, feel free to ask.

I tested those parts with a one-stud gap between the wheel axle and the white axle in the image below. There's plenty of gap. Hope this helps.

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Would this work with having one module in the center of the robot and a caster on every corner? That way it takes a lot less gears to drive and only one gear to turn.

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How would you turn?

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Having at least two modules is necessary (3 or 4 is probably best) for two reasons:

1. with only one module, swerving it would move the robot as well since there is no other anchor point for the module to rotate.

2. having multiple modules allows the robot to do tricky maneuvers - one module would allow only omnidirectional movement, and sacrifice the helpful maneuvers.

Re: pic: LEGO Coaxial Swerve Module
 

I just made a swerve drive using this module and it worked great for me. The only modification I made was with the bottom axel because it kept coming lose from the L brackets. I used a gray piece that was just longer than the original light grey piece and has an end cap on it. Two modules was all I used and for motors I had three of the small motors that come with the EV3.

Thanks for sharing this!

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Thanks for all of the replies! Thanks Nato for telling me about similar designs. They will be helpful if I run into problems.

I am progressing with the design of the robot as I await pieces to arrive. I think I will be using a set of 40 tooth gears and an NXT motor for turning the modules. I probably will use chain and the medium EV3 motor for turning the wheels. I will still have two motors left for other actions because I will control it with an EV3. After completing it, I think I will try to do some FLL missions to evaluate its viability for FLL.

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Strange that theres no pictures of this outside of the render. I thought i would make it, and gear it for speed.

Heres the simplest one I could make with nxt 2.0 parts. surprisingly sturdy considering the drive motor is attached at literally at only one other point outside the drive shaft. Love the shaft catchy thingy.

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I think conservation of momentum would allow for conversion to angular momentum if going fast enough and have sudden enough changes of direction.

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Hate to resurrect a thread, but a friend and I decided to have some fun with our access to some NXT 2.0 kits and made a 2 wheel swerve using this design. The stacking he came up with is the most aesthetically pleasing thing I've seen all month. Didn't have time to program it, and I doubt we could have since I believe the nxt 2.00 motors use tachometers instead of encoders.

Still fun to drive though, with one phone controlling steering and the other controlling speed it vaguely resembles swerve movement.

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Pretty cool stacking design. I'm glad you could make use of my module design.

My parts finally arrived from LEGO today, so I worked on it some. Currently, I am using a EV3 with a four wheel crab setup. I am working on optimizing it, but I should get a video of it sometime when I'm done. This has been a fun project so far.

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I'm pretty sure it is actually an optical encoder regardless of how it is marketed. They are relatively good at position control, not sure about speed control. I think the only thing that would get in the way would be the unpredictability of the passive casters.

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The NXT (and EV3) motors all have optical encoders in them, not tachometers.

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Yup. Looked that up later. I have some pretty good pictures of it though, so not too hard to put back together when i get access to the kits again.