Quote:
Originally Posted by Andrew Lawrence
I wouldn't run a new drivetrain in season I haven't designed, iterated, built, tested, iterated more, and practiced with a ton in the offseason. It's too risky, and the drivetrain is never something you want to make too complex. 99.99999999999% of FRC games give no advantage to omnidirectional movement over a simple and reliable tank drive.
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I'd modify the above statement to something more like "I wouldn't try a new/unusual drivetrain type (octanum, mecanums, swerve, WCD) unless you'd iterated it before the build season." The drivetrain is very important to have high reliability - and quite honestly - omni-directional ability is more often wasted or used less efficiently than it is used excellently. So, unless you're making the drivetrain 70% of your focus and will have a first iteration done Week 3 so you can test it and re-iterate it during the build season, don't use this octanum for next year's game. (and, as a side-note, I can almost guarantee now that the game won't be one for which the drivetrain should consume 70% of your effort... I don't think there ever has been such a game).
Regardless, I want to make some comments directly on your design...
I've never built an octanum, but I have to say they are one of the coolest drivetrains out there. They're heavy, but they're a very cool drive style that really brings the best of omnis and traction wheels together. I would think that they have an advantage of having less devestating failure modes than a swerve... basically, they would be more likely to only limit your capability in a match rather than leave you dead-in-the-water.
Your module is very slick-looking, but I am concerned about it's ability to parallelogram/rack... (i.e. the plates remain parallel to each other, but translate with respect to each other). Adding some standoffs that hold it together is the easiest way to help this.
I'm not familiar with mecanum gear ratios, but designing for a free surface speed of 15fps is probably good... I know mecanums have a surface speed loss due to the competing velocity vectors that are derived from their geometry. Your effective speed would probably be around 10-11fps after efficiency losses and "mecanum losses," which I'm guessing is a good speed for mecanums, but others should chime in on that...
I'd recommend using less of a reduction from your mecanum to your traction wheel... I'd probably gear for 6-7 fps on your traction wheel so you have a bit more speed but should still be traction-limited. If you want to know more about gearing drivetrains to be traction-limited, optimize distances traveled, etc. there are many great threads already around...
I don't know how your piston will mount to actuate, but if you're putting it somewhere in the middle (which seems likely to help minimize bending forces) it looks like it'd be interfering with the mecanum.
Looks good, but I would strongly recommend using something simpler this next year! It's always hard to not go with the flashier system, but in both short- and long-term sticking to a more reliable drivetrain next season that gives you 80-95% of the performance is the right choice*.
I would actually say that unless you have a very highly practiced drive team with your omni-directional system, the tank drive will give you better on-field performance.