Does this chassis look as if it would work?
 

A few other posts within this forum go into how Mecanum wheels would not be a good drive system type for this year's game. While we are considering pneumatic tires which are very likely to work, we are reluctant to lose the ability to strafe and quickly navigate the field. This is our current plan for our chassis which utilizes Mecanum wheels, and can be switched with the pneumatic tires at any time. This allows us to go to the competition with both sets of wheels and interchange them. The chassis has 6 inches of ground clearance. What is your opinion on the effectiveness of this chassis and drive system?


http://i.imgur.com/pJ9hPDj.png?1

Re: Does this chassis look as if it would work?
 

I just want to bring attention to this portion right here. How much time do you think you would be saving by strafing through the field rather than turning and driving straight? I'm pretty sure that I've seen calculations that show that turning and driving straight is actually more efficient in terms of time.

Re: Does this chassis look as if it would work?
 

I think it also depends on what type of game your playing. I find the mech wheels are good for helping to line up a shot. If your shooting it may help but otherwise I'm not so sure.

Re: Does this chassis look as if it would work?
 

I'm amazed to find the number of teams currently posting that are seriously considering mecanum wheels for this year's game. As a potential competitor against your teams, I am delighted to know this. But as a teacher and coach, whose goal it is to inspire as many students as possible to succeed and enjoy competitions like FRC, I strongly advise you all to simply eliminate mecanum from your list of options, NOW. Please.

Re: Does this chassis look as if it would work?
 

We were looking to shoot from the corner of the opposing teams courtyard, that way you don't line up a shot every time. Just go to the corner, slide in sideways, put the shooter at a prefigured angle, fire, and get out. With normal wheels you'd have to back into the corner while turning. Even then you can't guarantee a snug fit every time.

Re: Does this chassis look as if it would work?
 

Its always good to explain why, just so people dont have to ask "why would you say that?" and it takes more time to clarify.

Re: Does this chassis look as if it would work?
 

Sigh. Okay. Because mecanum precludes you from crossing terrain, especially of the types which our robots must cross for this game. A mecanum drivebase will get stuck on the first obstacle.

Re: Does this chassis look as if it would work?
 

This in theory is a good idea. But how are you planning on getting across the defenses to get to this spot with mecanum wheels. Also you need to be able to cross defenses reliably multiple time. I think this will cause more problems then its worth

Re: Does this chassis look as if it would work?
 

You are shooting a 10 inch diameter projectile toward a 16 inch opening that is at a 30 degree angle making the effective width of that opening about 13.5 inches from about 10 feet away.

I'm sure it can be done, but that looks to be about a 2 degree arc you need to be in and having been involved in building about 20 fields I can tell you that you cannot depend on that corner to be exactly square.

Re: Does this chassis look as if it would work?
 

Our robot design can go underneath the low bar, open the vertical gate, and can right the Cheval de Frise for crossing. Traction-wise and terrain-wise we we're skeptical about the Mecanum wheels due to reasons similar to those explained in this thread. We have both sets of wheels, so we'll just experiment with both and we can always go with the pneumatic tires.

Re: Does this chassis look as if it would work?
 

The field wouldn't ever be non-square by more than 2 degrees though would it? Given the size of the field wouldn't that be noticeable?

Re: Does this chassis look as if it would work?
 

There is a non-trivial value in having a spybot (re: [G7-E-ii]) which never crosses a defense barrier. If high goal accuracy of such a bot were high, I'd pick it as a first pick. But only if accuracy was high (and intake was 'touch it/own it' philosophy). I'd even go lower the drawbridge or open the door for such a bot if that was the predetermined match flow.

Mecanum - the biggest issue will be making sure the tabs don't get bent while crossing any of the platforms. It may be a good year to spend some weight on the Mecanum HD's from AM if you find the aluminum tabs bend or fatigue.

Re: Does this chassis look as if it would work?
 

It seems to me like you're accepting defeat too early there. Why cant you change the orientation of your shooter so it fires off the side. Or drive along one wall until you meet the corner?

Mechanum wheels are bad for pushing, add weight for your climb, and are simply inappropriate for many of the obstacles. Worse yet they aren't even necessary for the action you illustrated.

Re: Does this chassis look as if it would work?
 

I'm picturing a lot of bent screws on mecanum rollers.

I wish anyone who will be using mecanum wheels luck. I don't think the added benefit of strafing is worth the disadvantages, but I'm willing to be proven wrong.

Re: Does this chassis look as if it would work?
 

Could you explain what you mean by firing off the side? Do you mean against the castle walls or the guardrails? I feel like the majority of teams are going to insure their robot can adequately cross many, if not all of the obstacles. If we can be quick in shooting the ball and running back under the low bar to grab another one, and if we shoot extremely accurately. I see a very effective alliance and team strategy that could be put in place. As they damage defenses they feed balls into the courtyard, we can have them picked up and fired within 5-8 seconds.

Re: Does this chassis look as if it would work?
 

Pneumatic wheels have so much grip that you'd probably couldn't turn with this base. But, with mecanums, you have no viable way of easily getting over the defenses without a separate mecanism. If you want to be able to use pneumatic wheels as a backup, you'll probably need a 6-wheel center drop.

Re: Does this chassis look as if it would work?
 

I took it as meaning have your shooter face the left or right side of your drive train. That way there's no reason to need to strafe into the corner, just drive straight in up against the side of the field until you hit the wall the driver stations are on. That gets you into the corner with no fancy drive train, and a pretty simple manuver for your drivers.

Re: Does this chassis look as if it would work?
 

Maybe use a turret?

Re: Does this chassis look as if it would work?
 

Here is our chassis crossing the 4" bump in 2012 with AndyMark 6" mecanum HD wheels. Worked fine on the real thing with a fully loaded robot.

https://youtu.be/jl8pHpCjQtY

There were deflector plates at 45 degrees on both sides of the wheels that extended to about 2.5" above the ground. Our wheel modules were clam shells that surrounded the wheel, included the bearings, and mounted our toughbox nano gearboxes.

Re: Does this chassis look as if it would work?
 

This is not true, it makes it challenging but doesn't preclude you. There were plenty of robots who crossed the barrier in 2012 with mecanums, and that barrier was 4 inches tall by 6 inches wide.

Here are 4 videos of proof

Some use other mechanisms to help but they are still mecanum drive trains, and if they can cross the 2012 barrier, they can clear the Rockwall, and Moat easily. and honestly the Drawbridge, Portcullis, Sally Port, Ramparts, Chevalle de Frise, and Low Bar, have more to do with other parts of the robot then the mecanums themselves. So of the 9 obstacles mecanums can handle 8 of them with proper engineering, that isn't to bad.

Now I don't think mecanums are a good idea for different reasons but crossing the defenses isn't one of them.

Re: Does this chassis look as if it would work?
 

I'm no expert at modular systems but yeah that looks like it will work. Just keep in mind extrusions shouldn't go down on that design they should be up to keep the clearance. I'm interested in knowing why you would want the interchangeability.
I'm personally hoping the reason why you want the interchangeability is some dope strategy...

Re: Does this chassis look as if it would work?
 

We used big mecanum wheels during Breakaway...they did surprisingly well on those ramps. I think bigger ones could probably *manage* to get over most of the defenses.

However, we found out that even the impact of coming down off the Breakaway ramps eventually started bending the heck out of the roller support tabs, eventually jamming them. Later in the competition season a major pit task was fixing all the bent tabs....and at like 400 bucks for a set, we weren't in the position to have spares.

I think mecanums would eventually get wrecked in this game.

Re: Does this chassis look as if it would work?
 

We used mecanums in 2010 as well. Only year we've ever done it. I wasn't on the team at the time, but we still have the chassis from our 2010 bot with wheels still attached, and they seem fine. This could have just been constant fixing, or we just got lucky. Either way, mecs offer little that another drivetrain can't offer you in this game, at the expense of being more likely to struggle with the defenses. A decent driver should be able to maneuver this field easily on a tank drive.

Re: Does this chassis look as if it would work?
 

With the "rough terrain" and all the ramps, you are likely to bend the roller support tabs as Aur0r4 found. The team we were with in 2012 used the AM 8" Mecanums. If our robot ever touched the edge of one of the bridges when it was not straight on, even at low speed, it would bend some of those tabs. A jammed roller would cause the robot to drive erratically (normal and strafe). We got used to jacking the robot up between each and every match and having a crew of 4 people, each checking one wheel to make sure none of the rollers was jammed. If one was jammed, the bolt holding it on would have to be removed so that the tab could be twisted back "just right" using a pair of channel-lock pliers. This was not fun at all for the pit crew nor was it fun for the driver.

Re: Does this chassis look as if it would work?
 

It's no use being able to save time with mecanums if you get over the defenses into the opponents courtyard because you're using macanums