I agree. Crab (swerve) drives will most definitely be effective this year.
Mecanum drives will also be effective, because they are both able to get up the bumps and move with extreme maneuverability and moderate speed. The one downfall is that they have to be dead perpendicular to the ramp, or they will just drive sideways along it.
I tried this year to think about not using my favourite drivetrain (our linkage). But the more and more I thought about it, the more and more I think that our system would work out well. Basically a swerve system with a little less mobilty and less complexity should be well and capable of climbing bumps in at least one or both set ups.
I’d like to encourage teams to draw lots of diagrams, mock up rolling chassis, and think about the assumptions you are making before designing a “drive base”.
4WD skid - simple, effective, stable climber. If it’s designed to stand a chance in a pushing contest, it won’t be very maneuverable.
6WD skid / tank tread - a bit heavier, more moving parts, NOT a very stable climber, much more maneuverable, still good at pushing (Usually the best “compromise” chassis, but not this year).
Omni / Holonomic - very versatile, simple, maneuverable, but you’re on roller skates, and can’t climb well (or at all).
Crab / Swerve - similar to above but with superior traction, superior handling, more complex, many moving parts, not likely to be a good climber. Does not (usually) rotate the chassis efficiently which could lead to more complex (multi-sided) game mechanisms.
I think the best drive systems will be some sort of hybrid between two of the basics. I would NOT use a tread or a crab to climb… good luck to those who try it! (And do you really need to climb anyway?) If you do, you might want to bring a big tool box to the competitions!
Why would a tank tread design do poorly while climbing those bumps? I’ve heard the exact opposite: that tanks are great at it, and that they almost never break. I’m on an iPhone, so I can’t link to YouTube, but search up the Ripsaw MS1 made by Howe and Howe Tech (yeah, the ones from discovery channel).
The advice about checking assumptions and making design drawings and models is excellent, and there is a good list of drive concepts to consider here, as well.
However I would strongly encourage teams to check the assumptions made in the “basics” section of this post for themselves by looking at successful ramp climbers from the Aim High game, and step climbers from the First Frenzy game. Some of what is listed there, although no doubt well-intentioned, doesn’t reflect my personal observations of drive train abilities over the past six years.
Your reasoning behind many of these suggestions is very flawed. Your references to 6wd robots that fail to climb the ramp are inaccurate generalizations. I have yet to see a ramp that a well designed and well thought out 6wd with very good CG cannot overcome.
Also, this may be the year we see a 6 wheel swerve system. Although I would never doubt someone like WildStang designing a 4 wheel system that can overcome the bump this year.
When I first started analyzing the game I figured that a basic 6 WD robot with 8" wheels could easily climb the bumps. In this configuration there is no bottoming out issues, and the CG can be kept quite low.
However, we discovered a critical flaw when we tested this.
When a 6 WD robot climbs a ramp*, the center wheel acts as a pivot as the robot climbs over the crest. This results in half the robot being lifted into the air :eek: Highly unstable!
Take a look at the demo bots in the game vid (The non-animated ones of course!). They all have FOUR wheels. This is a much more stable configuration b/c all four wheels remain in contact as the robot climbs. There are no sudden rocking movements forwards or back.
Of course, as Dean himself pointed out, 4 WD robots don’t turn very well…
Checking your assumptions at the door is definitely important. For instance, the Aim High ramp was only 30 degrees to a nice flat with a wall behind it. The Bump (caps make it scarier) is 45 degrees up, to a flat with a 45 degree faceplant just waiting for the unwary or timid driver.
Before picking a drivetrain, you should consider how it’s going to rest on the slope, what that implies for your CoM, and what a sudden stop will do to you on the down slope. Or a sudden start on the upslope. You may want to mock up a bump and throw a drivetrain at it to see the effects momentum can have on your robot. I can tell you that a robot with more than 3 contact points per side should worry about having a CoM higher than 12". The case for a 6 wheeler is going to depend on the wheel sizes and separations, though it should be somewhat better.
EDIT: As Martin Taylor pointed out, numerous contact points on a side means you significantly raise your CoM before your robot tips onto the flat of the bump. Which would be survivable if the flat was, say, 24" long. But a 12" flat isn’t a large landing pad. If you have a CoM over 12" in the center of your bot, then once you tip over to the flat of the bump, your CoM is already past the far side of the flat. Which means you just keep tipping forwards. Which means you’re going to faceplant on the far side of the bump. Moving your CoM rearward helps, but not as much as you’d think. Accelerating off the backside of the bump will probably spare you the faceplant at the price of an even rougher landing.
Something I don’t think has been mentioned yet, but is important:
At the kickoff, after the Game Animation, Dean and Woodie demonstrated the difference between using the “slick” wheels and “stick” wheels when it came to the vision tracking.
If we use the “slick” wheels, the robot will have an easy time sliding around lining up with the vision target. However, it pretty much can’t make it over the bump (gets stuck at the top)
If we use “stick” wheels, we can make it right over the bump, but it can’t move sideways to line up with the target.
So if we go with treads, what kind of sideways motion is there to be expected? Sure, treads can go right up and over the bump, but you’d have to resort to tank-drive driving to line up with anything. Not exactly an effective solution, at least in my mind.