Grippy Mecanums

[Kevin Ray]

Originally Posted by EricH

No, it wouldn't. You're confusing mecanum and omni.

Mecanums do not roll sideways easily. They go front and back. They'll go at a 45 degree angle if you only have one. But sideways, especially if you've got all four on the robot, not so much.

You are right. They are not Omni's. We've used both. Though they don't roll easily, they do roll. Try pushing a macanum bot sideways when it is not powered. What I was trying to explain to SuperNerd256 is that a macanum bot in most orientations would roll off the tilted bridge with no power applied to prevent it. And, while we are at it, given identical gearboxes and friction coefficients of wheels, macanums would lose in a head to head with conventional wheels. This is possibly what SuperNerd256 was referencing.

[EricH]

It's a lot easier to push a mecanum, unpowered, forwards and backwards than sideways. There are four aligned axes of rotation instead of 4 axes at 90 degrees to each other.

As for the rest, read the thread and hope Ether doesn't come in and apply physics to show you exactly how wrong you are.

[MichaelBick]

Originally Posted by Kevin Ray

You are right. They are not Omni's. We've used both. Though they don't roll easily, they do roll. Try pushing a macanum bot sideways when it is not powered. What I was trying to explain to SuperNerd256 is that a macanum bot in most orientations would roll off the tilted bridge with no power applied to prevent it. And, while we are at it, given identical gearboxes and friction coefficients of wheels, macanums would lose in a head to head with conventional wheels. This is possibly what SuperNerd256 was referencing.

You could implement some type of brake, electronic or physical. Either way, traction is only half the problem most teams have with mechanums. When strafing, you have less than 100% power and speed off a traction drive(I believe close to 60%). Therefor, in many situations a traction drive can get to the same place as a mechanum in equal or less time, even if there is a turn involved.

Originally Posted by Kevin Ray

You are right. They are not Omni's. We've used both. Though they don't roll easily, they do roll. Try pushing a macanum bot sideways when it is not powered. What I was trying to explain to SuperNerd256 is that a macanum bot in most orientations would roll off the tilted bridge with no power applied to prevent it. And, while we are at it, given identical gearboxes and friction coefficients of wheels, macanums would lose in a head to head with conventional wheels. This is possibly what SuperNerd256 was referencing.

Kevin's right; That's what I'm referring to.

[Andrew Schreiber]

Originally Posted by SuperNerd256

Kevin's right; That's what I'm referring to.

Except Kevin is wrong. I've tried pushing unpowered mecanums sideways (software testing for 2337 in 2010). I was physically unable to push the robot sideways. Along the diagonals was a different story though. Still not easy but most definitely easier. None of this involved any sort of fancy software which would enable the wheels to hold position.

As for grippy mecanums, if you ever get a chance talk to 357 about their process. Their wheels have quite a bit of grip and they are one of the few teams I've seen use mecanums well.

However, I am a firm believer in the theory that if you are pushing with a mecanum wheeled robot you are doing it wrong.

Originally Posted by Andrew Schreiber

Except Kevin is wrong. I've tried pushing unpowered mecanums sideways (software testing for 2337 in 2010). I was physically unable to push the robot sideways. Along the diagonals was a different story though. Still not easy but most definitely easier. None of this involved any sort of fancy software which would enable the wheels to hold position.

As for grippy mecanums, if you ever get a chance talk to 357 about their process. Their wheels have quite a bit of grip and they are one of the few teams I've seen use mecanums well.

However, I am a firm believer in the theory that if you are pushing with a mecanum wheeled robot you are doing it wrong.

I know Kevin posted twice, so maybe we're reading separate posts. I'm agreeing to http://www.chiefdelphi.com/forums/sh...1&postcount=14

Mainly the part about the mecanums rolling off a tilted bridge if the power was disabled, and how they aren't as good in pushing matches.

And I agree 100% on your last statement.

[EricH]

Originally Posted by SuperNerd256

I know Kevin posted twice, so maybe we're reading separate posts. I'm agreeing to http://www.chiefdelphi.com/forums/sh...1&postcount=14

Mainly the part about the mecanums rolling off a tilted bridge if the power was disabled, and how they aren't as good in pushing matches.

Sideways, I'm not entirely surprised. However, mecanums have a lot of sideways motion resistance. Maybe they shouldn't in theory, but they do. So if they go off a bridge, sideways, it may be because they've got another robot driving them downwards, and there isn't a lot of friction. But, under normal circumstances, a mecanum won't go sideways without a lot of power applied, either by a pushing force or by the motors. Or sliding on low friction, which is a common problem with just about every type of drive known to roboteers.

Mecanums aren't as good in pushing matches because they aren't designed to go into them. They're designed to avoid the pushing match if possible.

[Hawiian Cadder]

Originally Posted by Andrew Schreiber

Except Kevin is wrong. I've tried pushing unpowered mecanums sideways (software testing for 2337 in 2010). I was physically unable to push the robot sideways. Along the diagonals was a different story though. Still not easy but most definitely easier. None of this involved any sort of fancy software which would enable the wheels to hold position.

As for grippy mecanums, if you ever get a chance talk to 357 about their process. Their wheels have quite a bit of grip and they are one of the few teams I've seen use mecanums well.

However, I am a firm believer in the theory that if you are pushing with a mecanum wheeled robot you are doing it wrong.

If the mechanum robot in question was running direct drive off bane bots P-80's then it is more than likely caused by binding in the gearboxes due to side loading. We had this problem in 2010, P-80's don't appreciate side loads at all, and without proper collars or flanges on the axle to load the frame instead of the gearbox this can cause inefficiencies for mechanums going sideways. I still wouldn't consider anything short of rough-top/wedgtop or pneumatic wheels to be really "high grip" in FRC.

[Andrew Schreiber]

Originally Posted by Hawiian Cadder

If the mechanum robot in question was running direct drive off bane bots P-80's then it is more than likely caused by binding in the gearboxes due to side loading. We had this problem in 2010, P-80's don't appreciate side loads at all, and without proper collars or flanges on the axle to load the frame instead of the gearbox this can cause inefficiencies for mechanums going sideways. I still wouldn't consider anything short of rough-top/wedgtop or pneumatic wheels to be really "high grip" in FRC.

They were toughbox innards (lightened) in a custom case.