Mecanum on the bridge?!

[Duke461]

Not to rain on people's parades here, but.....
***Before I go on, I feel I need to point out that I do have experience with Mecanums. 2 years. 1.5 years driving***

• In that first video, some on the other side is holding the ramp up (or down, however you look at it). Now, I can't prove it, but I'm pretty darn sure that that helps the robot get up.
• It took a long time to get up that ramp. Too long.
• 1 out of 5 times that drivetrain will probably fall off, unless you go super slow, which in that case see Bullet point #2
• What happens if for some reason you can't go over the bridge that round? Mecanum's will have an extremely hard time maneuvering the ridge.
• The material on that bridge was different than that of in the real game
• In the second video, the Mecanum's were having a very hard time getting up the bridge (not too sure how it helped Mecanum's case). If anything, it shows that carefully done programming will be required just for your drivetrain.
• The more top heavy these robots become, the harder it will get.
• A preponderance of team's this year will have a strong hard pushing robot. Good luck scoring on one. It's not fun.

Please take my criticism in a constructive manner, as I will do the same.
-Duke

[Djur]

Originally Posted by Duke461

Not to rain on people's parades here, but.....
***Before I go on, I feel I need to point out that I do have experience with Mecanums. 2 years. 1.5 years driving***

• In that first video, some on the other side is holding the ramp up (or down, however you look at it). Now, I can't prove it, but I'm pretty darn sure that that helps the robot get up.
• It took a long time to get up that ramp. Too long.
• 1 out of 5 times that drivetrain will probably fall off, unless you go super slow, which in that case see Bullet point #2
• What happens if for some reason you can't go over the bridge that round? Mecanum's will have an extremely hard time maneuvering the ridge.
• The material on that bridge was different than that of in the real game
• In the second video, the Mecanum's were having a very hard time getting up the bridge (not too sure how it helped Mecanum's case). If anything, it shows that carefully done programming will be required just for your drivetrain.
• The more top heavy these robots become, the harder it will get.
• A preponderance of team's this year will have a strong hard pushing robot. Good luck scoring on one. It's not fun.

Please take my criticism in a constructive manner, as I will do the same.
-Duke

• I was holding the opposite end of the bridge up to allow the robot on because it doesn't have a lowering mechanism (last year's bot). The robot moved under its own power the entire time.
• There's uneven friction on the mecanums and the fiberboard is ~3x more slippery than the actual Lexan surface, so it takes longer to drive up.
• The drivetrain will not fall off the robot (if that's what you meant), nor will the robot drive off the edge if there's a careful driver.
• Not really. Mecanums still have good grip on the surface of the bridge.
• Not my robot, so I don't know what's up in that video.
• That applies for every robot, too.
• I can't see how that's applicable specifically to mecanums.

Hope this helps.

[ThirteenOfTwo]

Originally Posted by Duke461

[*]It took a long time to get up that ramp. Too long.

Slippery surface, high CoG robot, early test. Our tests show it doesn't take nearly that long.

Originally Posted by Duke461

[*]1 out of 5 times that drivetrain will probably fall off, unless you go super slow, which in that case see Bullet point #2

The bridge has more than enough maneuvering room; if you fall off it's because you drove really badly.

Originally Posted by Duke461

[*]What happens if for some reason you can't go over the bridge that round?

Find me an opposing robot blocking your bridge and I will find you a nine-point technical foul. Besides, bridge traffic is likely negligible.

Originally Posted by Duke461

Mecanums will have an extremely hard time maneuvering the ridge.

Mecanums can have wheel guards and wedges built in, same as any drive.

Originally Posted by Duke461

[*]The material on that bridge was different than that of in the real game

But it had less friction.

Originally Posted by Duke461

[*]A preponderance of team's this year will have a strong hard pushing robot. Good luck scoring on one. It's not fun.

Score from the key.

[rocknthehawk]

Mecanum wheels have real world applications. Airtrax has video of their forklifts climbing stairs and bumps with them. With the appropriate size wheels and design, i'm not sure why there is a debate.

[Duke461]

Hopefully im not making this too much of a back and forth argument.....

Originally Posted by Djur

• I was holding the opposite end of the bridge up to allow the robot on because it doesn't have a lowering mechanism (last year's bot). The robot moved under its own power the entire time.
• There's uneven friction on the mecanums and the fiberboard is ~3x more slippery than the actual Lexan surface, so it takes longer to drive up.
• The drivetrain will not fall off the robot (if that's what you meant), nor will the robot drive off the edge if there's a careful driver.
• Not really. Mecanums still have good grip on the surface of the bridge.
• Not my robot, so I don't know what's up in that video.
• That applies for every robot, too.
• I can't see how that's applicable specifically to mecanums.

Hope this helps.

• I know, but i think the fact that the bridge isn't going to move no matter what helps the robot. Not too sure, so let's drop that one.
• Again, not an expert on this aspect, but I think Mecanum's act differently in that they need less friction ( or more friction) than most wheels to work properly. I'll conced this since i can't really support that.
• I meant the entire robot, sorry for the confusion. And notice you said IF the driver drives carefully. Please note again my original second point on how long it will take, and how driving carefully lengthens the time. In addition to this, other factors besides careful driving can affect this. And no, it does not have to be done in the means of a technical foul.
• Again, I can't mathematically support my claim, so i will concede this.
• Not everyone has your robot either. I made this point as a generalization for Mecanum', not necessarily yours in particular.
• Correct, but wheels that have higher friction (e.g., pneumatics) will mitigate the CoG issues.
• I don't know if you've ever played offense in a real match with mecanums with a decent defender. But I have. And for a good defender to push you around is as easy as beating a 2nd grader in basketball.

Round two.

Originally Posted by ThirteenOfTwo

• Slippery surface, high CoG robot, early test. Our tests show it doesn't take nearly that long.
• The bridge has more than enough maneuvering room; if you fall off it's because you drove really badly.
• Find me an opposing robot blocking your bridge and I will find you a nine-point technical foul. Besides, bridge traffic is likely negligible.
• Mecanums can have wheel guards and wedges built in, same as any drive.
• But it had less friction.
• Score from the key.

• I disagree. Too long. (stalemate here)
• Not true at all. Many factors determine driving--jjust one of them is the driver's skill. There's no reason to rely on the driver's skill when designing a robot.
• Find me a Regional with every robot code working properly and I will find you the 2013 FRC Water Game Designs. You not making it onto the bridge is not exlusive to technical fouls.
• Why overdesign when you can use other wheels that don't need these ridges? Have you proven yet that these wedges will be effective enough? (In no way am I saying it can't be done.)
• See my earlier point higher in this post. I will concede this.
• Why are assuming you will always be on the key? If I were a defensive driver, there would be plenty of way i could keep you off the key, directly and/or indirectly.

-Duke

[ThirteenOfTwo]

Originally Posted by Duke461

• I disagree. Too long. (stalemate here)

No point in continuing to argue this one, we just disagree. We'll see once I've got [S]better[/S] prototypes on my end.

Originally Posted by Duke461

• Not true at all. Many factors determine driving--jjust one of them is the driver's skill. There's no reason to rely on the driver's skill when designing a robot.

Maximum width of robot including bumpers is 36 inches. Maximum wheel-to-wheel distance is more like 26. You have more than a foot of room to misaim... if you fall of the bridge in the process of crossing it, your driver did something horribly wrong, no matter how good your software is.

Originally Posted by Duke461

• Find me a Regional with every robot code working properly and I will find you the 2013 FRC Water Game Designs. You not making it onto the bridge is not exlusive to technical fouls.

So, uh, you're saying that we could be blocked from crossing the bridge if two robots independently break down in front of two separate bridges and are too heavy to be pushed out of the way? The odds of that are so negligible that it's hardly worth discussing.

Originally Posted by Duke461

• Why overdesign when you can use other wheels that don't need these ridges? Have you proven yet that these wedges will be effective enough? (In no way am I saying it can't be done.)

Or you could just not design for the ridges. It's not like they're necessary to cross for most robots. (If all three robots on an alliance are regularly crossing midfield, think of the time wasted!) I haven't tried the wedges, but I'm 99% sure they'll work. Remember, any drive built to cross the ridge needs an elevated chassis to avoid high-centering anyways, so all you're adding is extra metal plates.

Originally Posted by Duke461

• Why are assuming you will always be on the key? If I were a defensive driver, there would be plenty of way i could keep you off the key, directly and/or indirectly.

I'm not assuming you'll be there, I'm saying you can get there. Maybe there have never been good tank drive defense robots at my regional, but I kind of doubt that. Pushing mecanum drives is indeed fairly easy, but it's not pushing them around that's the hard part of defense, it's maintaining the push.

[Duke461]

I'm too lazy to continue this argument, and frankly, it's stupid to continue it. You'll find out once you play with Mecanum's this year.
Can't say i didn't try.
-Duke

[dtengineering]

Originally Posted by Duke461

Not to rain on people's parades here, but.....[*]In the second video, the Mecanum's were having a very hard time getting up the bridge (not too sure how it helped Mecanum's case). If anything, it shows that carefully done programming will be required just for your drivetrain.[/list]Please take my criticism in a constructive manner, as I will do the same.
-Duke

I don't think you're raining on anyone's parade by providing practical advice based on your experience, however the intent of the video I posted was not to show that "it is easy to do", but rather that "it can be done", and (as you have correctly emphasized) to point out that software can make a huge difference in how mecanums behave.

In the bigger context, though, your experience with mecanum drives clearly shows. Every benefit provided by mecanums comes at a cost. Even the added mobility, which many see as a pure benefit, comes at the cost of additional driver training and practice driving time to fully utlize it.

The year we built mecanum the added complexities of our drive (and other mechanisms) meant that we did not have the final, working robot ready until about 2 hours before the FedEx truck arrived. It wasn't until the end of our second regional before our driver was truly able to intuitively take advantage of our increased mobility to deke out other robots. It was AWESOME when it worked... just beautiful, really... but until then we wasted a lot of time in pushing battles where our mecanum really didn't help.(Although it didn't hurt nearly as much as we had expected... we could hold ground with many robots and actually push some with 2 motor drives or poor gear choices.)

In our final year of competition we built a torquey 8 wd machine that could accelerate, stop, turn 90 degrees and accelerate in about the same amount of time that the mecanum could drive forward, then strafe sideways. It was an easy build/program (not that mecanums are particularly hard to program with the cRio), a top pushing machine that could "get air" off the bumps and, in the end... very close to as maneuverable as the mecanum.

But it wasn't as cool.

Duke has it right... there are lots of good reasons why mecanums aren't the best choice for this year's game... or for any year's game. But they do work, they CAN climb, and they are very, very cool.

Our mecanum robots competition life was over in a few months, but five years later I still have people asking me "what's with those wheels?"

If you haven't built/driven a mecanum, you owe it to yourself to try it at some point. Maybe this year...?

Jason