Ommni Wheels...

Especially in the past two years, there has been a noticeable increase in upper tier teams using an all ommni drivetrain, or “slide” drive. With prominent Texas teams 3310 and 2848 running slide in 2017 and 3847 and 3310 again in 2018, what advantages does running all ommnis have over more traditional tank or WCD drivetrains? Why do teams run slide over mecanum- both are easliy pushed and can take turns well, but mecanum has the added bonus of controlled lateral movement?

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Autonomous maybe? Other than that I don’t quite understand why you’d use a full omni drivetrain in this years game…

I suppose it’s not AS vulnerable as mechanum so maybe that’s another reason.

We (and a lot of other teams) used omnis on the corners and high grips in the middle. It works out pretty well for maneuvers, but doesn’t leave us vulnerable.

If you dig through some other threads that I’m too lazy to search right now, Paul Copioli (3310, formerly of 217) spells out some of their logic for using Omni wheels on their skid steered robots. The gist of it is that 217 lost on Einstein in 2011 because their robot with all traction wheels got “T-Boned” by 973. With all Omni wheels on both robots, 973 was able to very effectively control and slow 217’s movements, as 217 couldn’t break away effectively from 973 hitting them from their side. In an effort to prevent this from happening again, Paul opted to use lower traction wheels (Omni wheels) on his drivetrains in the future, enabling his teams to spin more freely out of those situations. He goes into greater details about the changing strategies of FRC scoring in that post (having the traction to hold your position while scoring is less important in games that have protected zones or defacto protected zones while scoring).

One other advantage to Omni wheels include reduced friction while turning, which in turn means needing less torque from your drive motors in order to turn. Needing less torque from your drive motors options up the option to run more aggressive gear ratios in your drive, if it suits your strategy and practice resources. It also can simply mean placing less load on your motors at whatever drive ratio you choose, meaning your motors will draw less current and stay cooler during operation.

I’ve also noticed the way these teams drive their bots is seemingly more natural than their counterparts. For example, 694 this season changed their drive wheels to omnis and after doing so, danced on the field so to speak. It looked so effortless. It’s unclear to me if that comes down to driver practice (all the teams mentioned thus far have identical practice bots) or the drive system.

For sure something my team will be playing around with in the offseason.

The inherent problem with mecanum is reason they allow you to move sideways. To get your mecanum drive to move sideways you drive your wheels towards or away from each other. When the wheel “fight” each other you get lateral movement. This makes them unpredictable if your being pushed or trying to get out of a pin. Instead of your drivetrain power being applied to go forward like an omni wheel you end up wasting power by pushing yourself not only forward but also in an unintended direction.

Its not directly related to the omni wheel question, but strategically I think a recent revelation that I’ve had is somewhat linked to the explanation above.

I was discussing “defense” with 7190 earlier this year. The students were wanting to add more mass to the robot so they could play better defense and win more pushing battles. I started out playing the “devils advocate” for the reverse position, and convinced not only them, but myself, that lighter robots are likely to be better defenders.

In short, if you’re playing defense and you’re in a pushing battle… you’re winning. It doesn’t matter whether you win the pushing battle, or lose the pushing battle… the simple fact that your opponent is in contact with you and not scoring while they push you around the floor means that you are fulfilling the defensive role. Have you ever tried running with a three year old child clasped to your shin? You are only ever so slightly more mobile with a three year old taking you down than you would be with a 250 pound linebacker lying on top of your shattered pile of bones. When intimidation and injury is outlawed, then you only need to be annoying to be effective.

The trick is to be able to get into your opponent’s path… or, in the case of offense… avoid it. That requires quickness and in general the lighter robot is the quicker robot.

It’s actually taken me 15 years of FRC to clue into this, but 7190 is in Houston right now. We can’t have been THAT wrong. :smiley:

I think I could be convinced to try an all omni drive system in the future… it might get pushed around easily, but if you’re an offensive robot in a pushing battle, then you’re losing, and if you’re a defensive robot in a pushing battle then you’re winning. The “winner” of the pushing battle itself is largely irrelevant.

Anyway, I’ve been a little slow to clue in, but I’m definitely in the light, quick, maneuverable camp now!

Jason

Are team (team 107) used a full ommni wheel drive base in 2017. It made us very fast a agile on the field with putting gears up but when it came to pushing matches we did not do well and the robot was a handful to drive.

We’ve chosen full omni drive because of mobility and wouldn’t go back plus we pull of some really nice drifts. We are prototyping with full omni wcd using vex polycarb 2x1 we love having light quick agile bots and omnis help us out a lot

We did this in 2016 with REALLY great results. We weighed in at 70lbs, and played some really great shut down defense.

Omni wheels are really great. Especially when it comes to turning. Again like what everyone else is saying here, when pushed from the side, you have just became the most GP drive train; you let other people tell you where to go:p

When having an all omni drive though, it is really important to have gear ratios that can get a team out of a “T-Bone” situation when you are flying down the field attached to another team’s bumper. We had a slow H-drive last year and we were pushed several times into the penalty zone. It could have been easily avoided if we could have just spun out from in front of them or just avoided them in the first place.

From what I have seen, most teams who are running all omnis are definitely taking a more offensive and speedy stance rather than a defensive one.

One of the biggest advantages of 2848’s drivetrain in 2017, aside from the greater mobility, was the ability to switch to traction wheels when trying to put gears up on the peg. If we were on omnis, then defense could shove us away a lot easier.

This is most likely because minor mistakes in the driving/stutters are usually diminished due to the sliding of the robot. If you watch 254 drive, they look pretty smooth, but then again I’m sure they have loads of driver practice.

We take a different route: if you have loads of grip AND loads of torque, you can power out of any situation, as well as move other robots out of the way at will.

74 used omnis quite a bit when I was on the team, although we never had a full omni drive train. We used omnis either in the front and back or just the front to allow greater maneuverability while maintaining pushing power when needed due to the traction wheels we put on the rest of our drive train. Worked great in 2014 and 2015.

I think one of the main reasons why 7179 is so good at the regional level is because of their omni-wheel drive train. Their driver is so good at whipping that little robot around the field. The drifts are so clean, and the movement around the field is so effortless.

Their driver just really knows how to get that robot from point a to point b, in such a stylish way. Love it

Omni wheels will allow easier turning. Remember that unless you understand the controls challenges - all omni wheels will make turning TOO easy. You’ll find it hard to drive straight, and even harder to control the ‘whiplash’ as you go around turns.

Don’t go all omniwheels without understanding the challenges. Like 775 drivetrains - it sounds great until you run into all the real problems.

Omm…

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This year we originally had 8 wheel 6 inch pneumatic tires. After we bagged the bot we started talking through all of the issues that the robot had. Three of the big issues were brownouts, weight, and bounciness (which made cube pickup tough). Inspired by 3310 from last year we said that going all omni wheels solves all 3. We really fell in love with the drivebase and we actually found that it was way harder to defend us with this drivebase.
I think in the last 2 years an all omni drive is a good choice, but in a game like 2014 where the ability to play defense is important an all omni drive may not be ideal.
I think that without 3310 showing the world what you could do with all omnis, we wouldn’t have been brave enough to try it and stick with it. In the back of our minds we would have always feared the omnis and people being able to push us sideways. Thing is I prefer getting shoved sideways to getting stuck when a team tbones you.

I’ve nudged my old team towards the 4omni path and I don’t think they’ve had any regrets. With some practice it’s the easiest to manuever in, and in my experience/perspective, getting from point A to point B is what allows you to play defense and avoid it, not pushing power.

Omnis let you lay down the power in all circumstances but a head-on pushing match. If they’re sliding to the side, they maintain static friction- so in a T-bone situation you still have all grip available to you. In a turn you have all grip available to you (and no power losses). You can drift without losing static traction or having kinetic friction (so you can go that much faster around a corner).

Basically, most of the perks of a swerve with all the perks of a tank (and more since 4omni is super easy to package)

Something that I think teams that run 4omnis should do more is learn from FLL and make funnel-like ‘jigs’ that allow you to line up to field elements by just ramming into them.

Of course if games become more like 2002 then this is all invalid, or if you come up with a specific strategy that requires shoving other robots. But I think FIRST is making a push towards games with defense less like that.

Also because KANSEI DORIFTU https://www.youtube.com/watch?v=7z3EurqbXt8