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Unread 20-12-2011, 15:44
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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.
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Unread 20-12-2011, 16:57
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Re: pic: I was bored... so I designed this.

Thanks for all the complements about the render and design.

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

Quote:
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.
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.
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Last edited by Garret : 20-12-2011 at 17:03.
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Unread 20-12-2011, 19:29
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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?
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Unread 20-12-2011, 19:35
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Re: pic: I was bored... so I designed this.

Quote:
Originally Posted by craigboez View Post
Just out of curiosity, what are the benefits of 6 wheel swerve over 4 wheel swerve?
The benefit of a six wheel swerve over a 4 wheel swerve is that the six wheel can act like a standard 6WD.
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Unread 20-12-2011, 19:45
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Re: pic: I was bored... so I designed this.

Quote:
Originally Posted by O'Sancheski View Post
The benefit of a six wheel swerve over a 4 wheel swerve is that the six wheel can act like a standard 6WD.
that's only really an advantage compared to swerves that can't independently steer each wheel
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Unread 20-12-2011, 19:59
O'Sancheski O'Sancheski is offline
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Re: pic: I was bored... so I designed this.

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Originally Posted by Aren_Hill View Post
that's only really an advantage compared to swerves that can't independently steer each wheel
Was 1625s 6 wheel swerve coaxle?
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Unread 20-12-2011, 20:01
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Re: pic: I was bored... so I designed this.

Quote:
Originally Posted by O'Sancheski View Post
Was 1625s 6 wheel swerve coaxle?
I'll let the search function handle that question
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Unread 20-12-2011, 20:07
O'Sancheski O'Sancheski is offline
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Re: pic: I was bored... so I designed this.

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Originally Posted by Aren_Hill View Post
I'll let the search function handle that question
Found it.
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Unread 20-12-2011, 20:01
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Re: pic: I was bored... so I designed this.

Quote:
Originally Posted by O'Sancheski View Post
The benefit of a six wheel swerve over a 4 wheel swerve is that the six wheel can act like a standard 6WD.
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?
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Unread 20-12-2011, 22:32
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Re: pic: I was bored... so I designed this.

Quote:
Originally Posted by craigboez View Post
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?
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.
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Unread 21-12-2011, 09:40
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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.)
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Unread 21-12-2011, 13:43
MichaelBick MichaelBick is offline
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Re: pic: I was bored... so I designed this.

Also, the other solution is to drive each side independently, and then turn corners together.
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Unread 21-12-2011, 15:22
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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!
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Unread 24-12-2011, 17:29
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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.
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