Breakaway question: getting on platform with meccanum?

[RoboMaster]

Were there any teams who got on the platform from Breakaway using meccanum? Let me explain: driving on the bump and balancing in the middle, then driving the meccanum wheels sideways, i.e. strafing, along the bump and on to the platform. If not, did any of your teams think of it during the design process?

I'm just curious to know because I thought of it a second ago. It would solve the problem of trying to turn sideways on the bump to be able to drive forward on to the platform. But would meccanum wheels even work here? Is the platform too high up? If you had really thick meccanum wheels I think they would make the jump, just like those infamous meccanum fork lifts that can go up stairs (though the manufacturer doesn't recommend it )

[Joe G.]

If I recall, the platform was a good 6 inches from the top of the platform. Mecanum wheels are poor climbers in the sideways direction to begin with, a lip almost their diameter would be impossible.

I believe some teams with swerve drive had success in this endeavor, however.

[Chris is me]

You'd be effectively trying to climb a 6+ inch platform with two tiny crooked 1 inch "wheels". It's definitely far from doable.

[EricH]

To get onto the platform from the bump, assuming standard-sized mecanum wheels, you'd need to turn on top of the bump--there just isn't enough vertical clearance while going sideways to clear that lip. You could do it, but you'd need rather large mecanums.

For a wheeled vehicle, the approximate maximum size of vertical step it can go up is governed by the axle height. If you try to go up anything higher than the axle, you'll need either a really good coefficient of friction or an intermediate step of some form--an angle on your vehicle works as well. But a mecanum has at least 2 axle heights. One applies going forwards and backwards, one applies when going parallel to a roller--and then there's the one that comes into play when the end of a roller hits a wall. This one is the lowest one, and on your typical FRC mecanum isn't more than about half an inch off the floor. That's the maximum sideways vertical height it can climb without a ramp. Front-back, it's more like 3-4 inches, barely within range to get a robot onto the platform from the bump.

So, you couldn't strafe onto the platform; you'd have to go up like a 4WD--go up, spin, climb on. Now, with a bigger mecanum wheel, you might be able to do it.

[RoboMaster]

Hmm, yes 6 inches is a bit high.

Are there any Meccanum wheels available to FRC teams that would be big enough to possibly make this work? I think the biggest AM sells is 8 inch right? But of course you'd need something like 12 inch wheels...

[EricH]

Originally Posted by RoboMaster

Hmm, yes 6 inches is a bit high.

Are there any Meccanum wheels available to FRC teams that would be big enough to possibly make this work? I think the biggest AM sells is 8 inch right?

I think it's BYOMW (Build Your Own Mecanum Wheels) for that challenge. 2826 might be able to do it--they built an offseason robot last year with massive ones. Even that one would have trouble strafing onto the platform, though--for a (best-guess) 14-inch diameter wheel, the roller tips still look to be about 1/2 inch off the ground.

[RoboMaster]

Originally Posted by EricH

Even that one would have trouble strafing onto the platform, though--for a (best-guess) 14-inch diameter wheel, the roller tips still look to be about 1/2 inch off the ground.

I think you're looking at differently than me. I mean that not only do the maccanum wheels allow you to strafe on the bump, but the rollers would stick out enough that they would catch on the lip of the platform, pull the robot up as they turn, and continue to strafe on the platform. The rollers that are about at the level of the axle would grip on the platform.

Now that I think about it, that might not really work. The catching rollers would have to stick out farther than the others to be the only ones that catch on the lip of the platform. However, it still might work since all the rollers are angled.

[EricH]

Originally Posted by RoboMaster

Now that I think about it, that might not really work. The catching rollers would have to stick out farther than the others to be the only ones that catch on the lip of the platform. However, it still might work since all the rollers are angled.

Which is exactly why it probably wouldn't work. If you were at an angle (and mecanums can move at 45* if they're programmed right), you might be able to get up if the rollers could lock relative to the wheel.

Angle of the rollers won't help if you're going straight sideways. Let's say that they did catch, though, just for the sake of argument. If the platform had a lip (it doesn't), up-going rollers could catch as well as down-going rollers. Bam, you're going nowhere at best, and going onto your top at worst (one wheel locks up solidly). Same argument applies for a flat surface that gets hit broadside by a mecanum--down+up=nothing doing.

The fact that they're rollers doesn't help you much, either; they roll. CG is off the platform, so they'll want to roll off of said platform unless they're locked--at which point you get into either lousy strafing ability or lots of mechanical complexity to lock when you want to climb.

[Chris is me]

Another thing to consider is that the torque of lifting most of the robot's weight off of the tip of the wheels is pretty large - your drivetrain might not be geared to provide that much torque.

[RoboMaster]

Yeah, I see now how it really wouldn't work. Hmmm, well it was an interesting thought.

What I meant by the lip was just the edge/top/corner. Because it's a right angle, as apposed to, say, a vertical plane, it's something that a hook or catch can sort of grab on to. Think of a foot or large omni wheels grabbing onto the edge of the platform by their rollers.

[joek]

you could put a secondary drivetrain that is perpendicular to, and slightly above the mechanums, powered by FP motors, using traction wheels for this sole purpose