Swerve with terrain

Going into the 2023 season with the 2022 and 2020 season having mostly flat terrain with the exception of the cable protectors I wanted to ask how much terrain can swerve handle? I watched 254B in madtown of 2019 and they seemed to handle the bumps of the field just fine and where even able to drop from a level 2 with swerve. So would the terrain of games such as 2019 and 2018 work for swerve?

Related recent topic: Off-road swerve expectations if rough terrain field? - Technical / Technical Discussion - Chief Delphi

I think stock COTS swerve can definitely handle some bumps (e.g. 2020). I suspect the bigger the bumps are, the larger the wheels and greater the clearance may need to be, and there is some limit beyond which custom designs or at least modifications to COTS will be required.

Wheels are generally able to climb over bumps that are less than half the wheel diameter, especially when aided by other wheels in contact with the floor. So, if you have 4” diameter wheels, you will be able to drive over 1” - 1.5” bumps without much issue. 2” bumps are also possible, but you are going to have to drive over them relatively deliberately (i.e. approach them from a relatively perpendicular direction and probably use a particular speed or technique).

Anything greater than 1/2 the wheel diameter and you will need to design the robot with the terrain in mind. Several teams were able to drive with swerve over the 2016 terrain, but needed various special drivebase modifications to do so.

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Is there a measure for a sloped edge? In 2019 and 2018 for example the slope was much less steep then 2016 which had a slope and bar at the end. Although the end height may be high if the slope is more gradual it should fare just fine, right?

The general method is to put a protective “cone” or “ramp” around the module, attached to the frame. The idea is for the inverted cone to make contact with the obstacle first, causing the robot to ramp up onto the obstacle. When the wheel does come into contact with the obstacle the forces side-loading the wheel are significantly reduced as contact is made close to tangentially.

You do need to still be worried about high centering on the obstacle.

See team 16 in 2016, 1717 also managed in 2012. 2767 and 2337 (and probably others) also used this in 2020 to deal with the steel 2x1 tubes on the field.

Yes, keep this in mind. while 1/2 diameter is possible it is not practical in a time-based FRC game.

Personally I wouldn’t go over an obstacle more than more than 1/3 the wheel diameter with no protection, and even then that’s a stretch. The side loading forces are just too high with any speed, COTS modules are simply not designed for this application.

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In probably the most terrain based game we have had in the last 20 years 16 in 2016 handled everything pretty well with a relatively standard swerve drive.

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This was our implementation of this ramp in 2022.

The two important angles with regards to ramps/terrain are approach angle, and breakover angle.

Approach angle is usually the issue with swerve, as the relatively higher frame height with swerve solves much of the breakover problem for free.

There’s a third angle to worry about when the ramps have exterior corners called the ‘straddle angle’. Swerve usually gets this one solved for free as well with the typically square drivebases.

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One more small tidbit to add on here: with swerve you can drive “at 45 degrees” to decrease some of the clearance issues on most obstacles we see in FRC. I would still design around the worst case scenario, but in match play there may be better mobility performance to approaching an obstacle with a corner rather than a side.

FWIW leading with a corner can also transfer more energy to a small area when hitting something once the noodle in the bumper bottoms out and that damper is no longer available. So be careful around some parts of the field, or use this knowledge in “unique defensive ways”. Just be aware the loading will be higher on your bot too, in a corner with a drive module…

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Are these slide decks publicly available?

The slide decks were recently published here: WildStang Robotics Program: Team 111 and 112 Build Blog - 2023

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Full decks linked above (not fully polished).

Drivetrain specific presentation here: WS Drivetrain Presentation

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Another thing to consider with any significant terrain is tip over. Obstacles that act like curbs (the kind seen on the edge of some roads) can trip a robot, and robots with a high center of gravity are at increased risk of tipping over, as the robot both tilts and goes through rapid deceleration. Robots managed to trip over even the cable protectors. Add in powerful motors and swerve, and this can become a significant problem.

Driver training helps, but it’s usually worth trying to keep a low center of gravity. Don’t hit anything curb-like with the wheels sideways, as they can get caught up more easily than one might expect when facing this way.

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