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View Full Version : Pros & Cons of Carb/Swerve Drive Train.

team2061
08-01-2008, 21:48
Our team would like to go with this design but were not sure how to achieve this.Does anyone else have any other design and what are the pros and cons of a crab/ swerve drive train?


http://i67.photobucket.com/albums/h309/betox702xsincity/steeringidea.jpg
rachal
08-01-2008, 22:08
Woah, why do you need 6 wheels?

The big pro is the maneuverability. Cons: heavy, complex, drivetrain uses up lots of motors (well not too many with coaxial swerve), and it's unwise to try one for the first time under the time constraints of build.
EricH
08-01-2008, 22:14
Woah, why do you need 6 wheels?You only need four, or even three (team 16 in 2006). The two in the middle are extra weight.
team2061
08-01-2008, 22:16
Woah, why do you need 6 wheels?

The big pro is the maneuverability. Cons: heavy, complex, drivetrain uses up lots of motors (well not too many with coaxial swerve), and it's unwise to try one for the first time under the time constraints of build.

Our mentor thinks that 6 wheels is better but i personally think that the whole idea of a crab design is to complex.
EricH
08-01-2008, 22:18
Our mentor thinks that 6 wheels is better but i personally think that the whole idea of a crab design is to complex.In this case, you are probably right. 6 wheels is better than four wheels for skid steering, not crab drive. At this point, you should probably not try a crab.

Oh, and the biggest problem with your posted design is that those center wheels had better be omnis, otherwise you won't be able to go sideways (which is the main point of having a crab drive).
T3_1565
08-01-2008, 22:20
and it's unwise to try one for the first time under the time constraints of build.

I would agree, if you havent thought of how to build one before the build season, chances are slim that you will be able to finish it properly.

and I am also curious as to why you want to have 6 wheels. why not just the 4 steering wheels???
rachal
08-01-2008, 22:23
Our mentor thinks that 6 wheels is better but i personally think that the whole idea of a crab design is to complex.

I mean, why do you have a diagram of a 6-wheeled-swerve? Swerve only needs 4.

So your mentor wants to do a normal 6 wheel, and your team wants a swerve/crab? I'm confused :P
team2061
08-01-2008, 22:30
I mean, why do you have a diagram of a 6-wheeled-swerve? Swerve only needs 4.

So your mentor wants to do a normal 6 wheel, and your team wants a swerve/crab? I'm confused :P

the other way around, our team would like to go with a standard 6 wheel drive train with middle wheel lowered, but our mentor wants to go with a 6 wheeled swerve train for some reason,like the picture above
team2061
08-01-2008, 22:32
In this case, you are probably right. 6 wheels is better than four wheels for skid steering, not crab drive. At this point, you should probably not try a crab.

Oh, and the biggest problem with your posted design is that those center wheels had better be omnis, otherwise you won't be able to go sideways (which is the main point of having a crab drive).

Good point.
The middle wheels are not omni wheels but andymark wheels. Our mentor says that the middle wheels are for traction.
EricH
08-01-2008, 22:35
the other way around, our team would like to go with a standard 6 wheel drive train with middle wheel lowered, but our mentor wants to go with a 6 wheeled swerve train for some reason,like the picture above
There is no good reason to have a fifth and sixth wheel in a swerve. Unless, of course, he wants a Chariot (http://www.chiefdelphi.com/media/photos/29187) style of drivetrain... (The robot on top has a crab drive with four wheels.)

6-wheel dropped center is pretty standard; it's hard to get in trouble with that.
Raul
08-01-2008, 22:36
the other way around, our team would like to go with a standard 6 wheel drive train with middle wheel lowered, but our mentor wants to go with a 6 wheeled swerve train for some reason,like the picture above
Take it from me 6-wheel crab is overkill and overly complex. I cannot think of any advantage of adding the 2 extra wheels.
Did your mentor really mean that they want 6 wheels with monster-truck steering? Even in that case, 4 wheels would work best.
team2061
08-01-2008, 22:41
Take it from me 6-wheel crab is overkill and overly complex. I cannot think of any advantage of adding the 2 extra wheels.
Did your mentor really mean that they want 6 wheels with monster-truck steering? Even in that case, 4 wheels would work best.

I dont know what he's thinking, but I'll talk to him and my team about it.
Our mentor is an autotech teacher
Neil B
08-01-2008, 22:52
Yeah, as almost everyone else said, 4 wheels is probably best. Crab drive is heavy as it is; no need for extra wheels and weight.

What I've heard is a major problem with crab drive isn't so much the construction (although that's a task in itself) but the programming. You have to have sensors to make sure that all the wheels are pointed in the correct direction at the same time. Then you have to have a program to make sense of the data those sensors are sending to RC. All in all it's a tough job that probably should be started before the build season.