20-12-2011 13:33

Jared Russell

Re: pic: I was bored... so I designed this.

Any particular reason you are cantilevering the wheels on the swerve modules? Any time a bevel gear is involved, you generally want to be as structurally rigid as possible.

Other than that, looks like a great design and a fantastic render.

20-12-2011 14:58

MichaelBick

Re: pic: I was bored... so I designed this.

Amazing design and nice render. Also, the cantilevered wheel is so that the drivetrain can perform like wcd and swerve.

20-12-2011 15:06

JesseK

Re: pic: I was bored... so I designed this.

Careful ... WCD takes advantage of cantilevered design by pushing the wheels out as wide as possible; it's so far that it's not possible to put pieces of the frame outside of the wheel base unless the frame is above the top of the wheels. Doing so greatly aids in stability and turning. By design, setting the wheel base width as wide as the frame is not possible with coaxial swerve. Thus, the only benefit of this design is easy swap of the wheels (and potentially reduced manufacturing time) -- which, IMO, doesn't outweigh the benefits of a boxed swerve module.

Very sweet render nonetheless.

20-12-2011 15:18

thefro526

Re: pic: I was bored... so I designed this.

This point would only hold true if the wheel was further out in the chassis. As it sits right now, the wheel appears to be centered with the axis of rotation of the module. Odds are, the wheel was either cantilevered for weight or aesthetic purposes.

20-12-2011 15:44

Chris is me

Re: pic: I was bored... so I designed this.

I don't want to "slam" anyone who works this hard, so please don't take this the wrong way, but I think this system has a few problems.

First, your modules. Yes, cantilevered wheels offer easier access, but they are not the end-all be-all most important drivetrain feature in FRC. The reason my team cantilevers wheels is mainly for simplicity and weight. Cantilevering wheels in a swerve drive saves negligible weight (maybe a half pound?) and makes the whole wheel and module significantly worse supported.

In 2008, team 148 built modules much like yours, but with a fully supported wheel. Even then, the modules wore through bevel gears, I'm assuming due to the modules twisting causing excessive tip loading. You'll notice teams like 1625 and 1640, two popular coaxial swerve teams, go to great lengths to make their bevel gear setup rigid. 1625 used a "puzzle piece" method of connecting 1/4" plates while 1640 uses gussets to connect a piece of U-shaped extrusion together.

It also looks like your module support is a bit lacking. It looks like you have a single thrust bearing mounted to a piece of 1/8" metal plate supporting all of the forces on the module. That's a pretty extreme cantilever. A lot of teams use a lower support for at least extreme loading, or they support their modules in multiple places / over a wide area. Think carefully how you want to do this.

Swerve drives are tricky - that's why even well funded teams with many engineers don't get them right.

20-12-2011 16:57

Garret

Re: pic: I was bored... so I designed this.

Thanks for all the complements about the render and design.

I cantilevered the module just for fun and aesthetics of the module.

I have attached a section view of the module (not mounted to frame and without bolts). There may be support issues still but I did try to take into account as many of the load issues as possible.


(the image is a little squashed so it looks a little off)
About the module itself:
The main body of the module is machined out of a 3" long piece 5"x3"x1/2" Aluminum Angle. The top of the main body of the module is adapted from my teams current swerve drive module design. Also I did not want to cantilever the bevel gear so I went ahead and supported the bevel gear shaft on both ends. (This module was designed just for fun really so there may be issues I am unaware of). I welcome any advice and comments about the design.

20-12-2011 19:29

craigboez

Re: pic: I was bored... so I designed this.

Just out of curiosity, what are the benefits of 6 wheel swerve over 4 wheel swerve?

20-12-2011 19:35

O'Sancheski

Re: pic: I was bored... so I designed this.

The benefit of a six wheel swerve over a 4 wheel swerve is that the six wheel can act like a standard 6WD.

20-12-2011 19:45

Aren_Hill

Re: pic: I was bored... so I designed this.

that's only really an advantage compared to swerves that can't independently steer each wheel

20-12-2011 19:59

O'Sancheski

Re: pic: I was bored... so I designed this.

Was 1625s 6 wheel swerve coaxle?

20-12-2011 20:01

craigboez

Re: pic: I was bored... so I designed this.

I don't understand. Why would you go to the trouble of building an extremely complicated drive so it can approximate the functionality of a very simple drive?

20-12-2011 20:01

Aren_Hill

Re: pic: I was bored... so I designed this.

I'll let the search function handle that question

20-12-2011 20:07

O'Sancheski

Re: pic: I was bored... so I designed this.

Found it.

20-12-2011 22:32

Nuttyman54

Re: pic: I was bored... so I designed this.

Because it gives you swerve capabilities, but without the downsides of a 4wd. One of the significant downsides to a typical coaxial 4wd swerve is that it cannot turn on it's center very well (skid steer), for the same reasons that a 4wd has a harder time turning around it's center than a 6wd (if this concept is unfamiliar to you, there are many threads on CD that discuss the physics behind this, go look them up).

There are two main solutions to this: 1) do a module style (non-coaxial) swerve or an independently driven (ala Emperor Swerve by 973) which allows the wheels to always turn such that they are not skidding when making a center turn or 2) make your code so that you don't make turns like that most of the time (as 40 used to do, with quadra-steer).

If you add the extra set of dropped center wheels, you get all the benefits of a swerve drive, but you still have the non-swerve driving characteristics of a 6wd.

21-12-2011 09:40

thefro526

Re: pic: I was bored... so I designed this.

Just to add a quick point onto Evan's post: A 6WD swerve, in theory should also handle climbing objects a little better, depending on the object and the implementation of the swerve. A 4WD swerve would require quite a bit of ground clearance at the center, which may or may not be advantageous. A 6WD swerve would need ground clearance similar to a conventional 6WD. (For more clarification, look at some of the 4WD robots from 2010 vs the 6WD robots and you'll see what I mean.)

21-12-2011 13:43

MichaelBick

Re: pic: I was bored... so I designed this.

Also, the other solution is to drive each side independently, and then turn corners together.

21-12-2011 15:22

Foster

Re: pic: I was bored... so I designed this.

The title of this thread is "I was bored... so I designed this."

How much time did you spend on the design? I see a number of these every year and figure that there are hours and hours spent.

Thanks!

24-12-2011 17:29

Garret

Re: pic: I was bored... so I designed this.

Sorry for the late response I have been busy the past few days. I spent about 4 nights working on this design. I designed this in 4 stages, I started with the module design, then I designed the mounting set-up, then the frame, and then finishing the assembly. Each stage was about a day of design.

27-12-2011 04:57

Cory

Re: pic: I was bored... so I designed this.

removed reported spam image

27-12-2011 09:06

Isaac501

Re: pic: I was bored... so I designed this.

That design will eat bevels for breakfast. Nom Nom Nom teeth.

Since it's non-coaxial, when the module turns the drive will turn against it.

That said, VERY nice work, and just a gorgeous design.

The cantilever is not so much of a design problem - you're not going to be facing massive forces on the bushings. I don't see the bushings taking that much of a beating. You may want to consider beefing up the module itself though. It looks thin.

27-12-2011 10:01

Big Ideas

Re: pic: I was bored... so I designed this.

It's good to see some exploration of bearing options but the application of the thrust/needle rollers on the wheel drive shaft is problematic.

1) The keyway would not be compatible with the needle bearings.
2) The counter thrust for the thrust bearing at the wheel would be by the needle bearing housing or the frame member, which is not good. A preloaded pair of angular contact bearings would be better. There is no particular side thrust to keep the thrust bearing loaded.
3) The gear separating force from the tooth meshing + the torque from the robot weight will be bending the vertical plate. It may be better to continue the removable vertical plate down the the lower shaft, so that the wheel shaft is not cantilevered.
4) Why is the wheel contact patch offset from the pivot axis? My understanding is that you want to avoid the turning force from a wheel drag moment seen at the pivot. This moment could cause twisting, scuffing, excessive drive resistance and problems with rigging to drive straight.
5) Note that I am not itemizing the many things I like about the module design.

27-12-2011 16:20

Garret

Re: pic: I was bored... so I designed this.

I did not realize that, but now that I think about that it makes sense. I will change that, I was working on a version that used an angular contact bearing. I have not worked with them before so I wasn't sure how to approach them.

I had a version of this that has that plate extended down to the wheel shaft. On the newest version I have completely removed the cantilever (replaced the modules with our current modules)

That is a problem I have fixed that in the newest version.

Thanks for the comments, they have been very helpful.

Here is the newest version so far.