Effective Drive Base

[teampronto]

Originally Posted by =Martin=Taylor=

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 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...

*or a tracked drive

False. There is indeed a 6 wheeled robot.

[Kevin Sevcik]

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.

[hyperdude]

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.

[DanDon]

Originally Posted by hyperdude

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.

I've had no problem with tank-drive steering in regards to vision tracking in 2006 or 2007.

[Nathan2974]

Originally Posted by Kevin Sevcik

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.

I just wanted to point out that the actual grade of the bump is approximately 38.7 degrees (or something to that effect) using simple trigonometry based on the height and width provided by FIRST.

[hipsterjr]

We designed these articulating drive pods back in 2005 and have been waiting for a game like this to use them.

[dustinjeremy2k]

In response to several comments and questions regarding my reasoning for my dislike for 6WD and tread designs as a climber... Understand I'm not suggesting that they cannot climb. Of coarse they both can be extremely effective on inclines. But their MAIN advantages are massive weight distribution on unstable surfaces (tanks with treads in sand) and maintaining contact with extremely unpredictable terrain (rovers) when used with a suspension system.

So, my original post was under the heading "Basics"... and I was not considering anything with a suspension a basic design. In a basic (kit-bot) configuration the 6WD and tread option give you the same see-saw effect as you crest the peak of this games "bump". Not exactly the picture of stability. Toss in a reasonably high CG (needed for clearance in a static system) and the likelihood that your weight distribution will be biased in one direction to some extent, and well, I'm not interested. Two points in contact are by definition more stable…

We tested this out this evening as well (on a kitbot rolling chassis) and that's all I needed to see! Throw it together and see for yourself. Good luck.

[Seat Ninja]

Originally Posted by hipsterjr

We designed these articulating drive pods back in 2005 and have been waiting for a game like this to use them.

(stares with amazement)
...I...WANT...THOSE

[DiehardCybercard]

I'd like to thank everyone for all of their input!

I was hoping this thread would generate a good place for a few people to reference and learn. I've learned a lot from everyone's posts. Thanks all =]

[dustinjeremy2k]

Originally Posted by =Martin=Taylor=

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 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...

*or a tracked drive

Nicely put... I guess I was not as clear. And with all due respect to those that posted earlier, I've been doing this a while too, and played the games you referenced... and climbed with ease each time without a tread and less than 5 wheels! Very stable! Just trying to simplify a problem that’s easy to make unnecessarily complex.

[yoshibrock]

Currently, as a team, we're trying to decide between using mechs or a swerve system. I happen to be privy towards a swerve system, but it would be our first year using it, so a lot of people are nervous. I think that swerve would give better traction than mechs as well as the ability to have a multi-direction robot, but there are arguments against swerve as well (mainly how complicated it is). I guess I'm just a teensy bit biased

[roboticWanderor]

Originally Posted by Kevin Sevcik

Accelerating off the backside of the bump will probably spare you the faceplant at the price of an even rougher landing.

i think some fast robots are going to be surprised to see how much air they can get flying over that bump, such instances will make for some cool pictures for sure, structural integrity of the chassis not withstanding.

[DiehardCybercard]

that is a concern my team will have when we have the drive base argument. we built our first mechanum base this year in off season. so we are fairly new to exotic drive systems.

a big factor with a swerve drive though is that is a lot of weight added to your robot. the more weight you have on the robot the riskier it will be to drive over the bumps.

im really interested to see how teams approach this challenge.

[Madison]

For the sake of discussion, I'm attaching a picture that shows an 8WD system going over the bump.

[Akash Rastogi]

Originally Posted by Madison

For the sake of discussion, I'm attaching a picture that shows an 8WD system going over the bump.

Thanks.

We're debating between a 6wd with 8" wheels or an 8wd with 6" wheels. I'm personally leaning towards the 8wd.

Originally Posted by DiehardCybercard

that is a concern my team will have when we have the drive base argument. we built our first mechanum base this year in off season. so we are fairly new to exotic drive systems.

a big factor with a swerve drive though is that is a lot of weight added to your robot. the more weight you have on the robot the riskier it will be to drive over the bumps.

im really interested to see how teams approach this challenge.

False.

This weight is at the bottom of your robot, low to the floor. This amounts to a low center of gravity as long as your arm or hanger is also lowered while driving over a bump. Low CG= easier movement over the bump.