Quote:
Originally Posted by Ginger Power
What are the pros and cons for each drivetrain? What types of game fields are conducive for each?
For Swerve: what are the advantages to 4 wheel swerve vs. 3 wheel swerve?
For Butterfly: Also consider nonadrives and decadrives (a butterfly drivetrain with a strafe wheel or 2).
I'm trying to figure out what I should spend my time working on as I'm procrastinating on my schoolwork. I just keep going back and forth on which drivetrain offers the most benefit. For this comparison, ignore ease of design, and cost. Assume that the team looking to manufacture either of these drivetrains has access to a simple mill and lathe (no CNC).
In my mind, a decadrive and a swerve are comparable in weight, maneuverability, and cost. How about other factors like manufacturability, driver learning curve, and durability?
I'd also be interested to hear about what drivetrain would perform better in a game like Aerial Assist where there is a wide open field, assuming equal driver ability.
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I can answer your questions above about swerve, but I don't have enough experience with octocanum/any mecanum drive to talk about that drive system.
We have run swerve since 2010 (with the exception of 2016 - FIRST Stronghold - where we ran treaded tank drive), and we actually did some testing with a three-wheeled swerve. Check out
our website for our findings, as well as
this whitepaper from our head mentor (CD Username: Clem1640).
Swerve tends to perform better when the field is flat (2011, 2012 (mostly), 2013, 2014), consistently covered(2010), or a combination of the two (2015). The reason is that, to benefit from all of the drive motors with swerve, all wheels must contact the ground. If one picks up, your 4WD system becomes 3WD. We learned this the hard way with our
2013 robot, which relied on the drive motors to hook on to the side of the pyramid.
Without extensive modifications, it may struggle with fields that don't meet these criteria (2016). See
FRC 16 and
FRC 4143 for examples of some modifications that can be made to overcome field obstacles.
If you only have access to a mill and a lathe (no CNC), swerve may prove to be very challenging (more so than it normally is), but it isn't impossible.
FRC 2471 showed an example of a manually-milled swerve design of theirs a few years ago. More complex/adaptable swerves will require more complex manufacturing resources.
Swerve's learning curve is significantly higher than wheeled tank drive (in both field-centric and robot-centric driving modes). We have our drive teams practice extensively until it becomes second nature for them. We also have our controls set up similarly to Call of Duty and other games to help it feel more familiar for the drivers (I'm pretty sure the correct name for this setup is Halo drive).
Since swerve drives are so complex, they have multiple points-of-failure depending on the design. However, if your chassis is rigid enough and your swerves can't collide with field elements (we killed a lot of steering motors against the bridges in 2012), then they will be about as reliable as a standard or WCD tank drive. If you design it to be easily replaceable, then maintenance becomes exponentially easier.
For more information about swerve and how we use it, check out our
Swerve Central page. And check out
Ether's Whitepaper and
our 2015 code for help with programming a swerve drive. (The code linked is in Java. We switched from LabView to Java in the 2015 off-season. LabView code can also be found on our Github)
Hopefully this helps answer your questions about swerve drive, and hopefully someone with octocanum/similar drive experience can answer questions about that drive system.