Grippy Mecanums

[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.

[DELurker]

Originally Posted by Grim Tuesday

Get in contact with team 357, Royal Assault. They debuted Mecanums for FIRST usage, and if there will be a Mecanum robot on Einstein, it will be them.

Actually watched 357 shed half of a mecanum this season at Philly. As another team that uses mecanums, 1370 had tremendous success as a defensive bot, pushing other bots around the field. While mecanums do have their limitations, they are nowhere as bad as their reputation will lead you to believe.

[rocknthehawk]

Originally Posted by jblay

Make a swerve drive setup.

In all seriousness though the real issues with the mecanum wheels in terms of pushing are this:
-They aren't 100% effective at transferring power, a lot of it is lost. This forces you to have to gear higher to be able to go at a reasonable speed which makes you less capable of pushing. It is difficult to do a shifting gearbox with mecanum wheels because each wheel has it's own gearbox and shifting gearboxes are quite heavy.

Hope this helps. As a team that used mecanum wheels last year I would advise against them because when the eliminations roll around and you are facing defense, being able to be pushed sideways easily really hurts your chances and it makes winning very difficult.

Just a few points, as this debate is never-ending every year.

We geared our mecanums 17.5:1 (CIM shaft to wheel), and found this to be perfect. at 12:1 we were TOO fast. The same speed on last year's bot with kit wheels gave us a perfectly capable and quick base.

The weight of shifting 4 gearboxes isn't extreme. We use dewalt gearboxes, with a cim and mount it's under 5lbs each. For comparison, the AM super shifter is 4lbs without CIM's. The problem becomes shifting all 4 at the same moment.

This year is unique, where you've got a large protected area. An efficient mecanum can out maneuver a defensive robot, as we've done many times this year.

[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.

[kinganu123]

I just wanted to throw in that the rollers make a HUGE difference to the traction. The new AndyMark mecanum rollers don't have nearly as much traction on our 2011 not as our 2010 robot had (no idea where this were bought from, but it wasn't andymark)

[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.