Mecanum Einstein this year

[Henzado]

Originally Posted by Nemo

It does get to be a problem when you have 2 or 3 mecanum robots and you lack a good 6WD to play defense or play some other strategy that requires pushing around.

Although mecanum cannot push around as other drives, I would argue that mecanum wheels can play good defense. Take for example Curie qualification match 110, where we helped save the match against arguably the fastest minibot on the field. We were on the red alliance, the robot with the folding mast who dropped their uber tube. http://www.youtube.com/watch?v=aEnahGGj9dY

I would argue,(as well as our driver) that if it wasn't for our mecannum wheels, we wouldn't have been able to slow down the team from scoring, block their way to the tower and swerve away at the last moment, ultimately making the minibot come in last. If that minibot would have gotten first, the results would have had a different out come.

[AdamHeard]

Originally Posted by Nemo

I'll get one of my students to upload our videos, including the ones against 973. What you will see is a mixture of two things: 1) 973 wasting a good chunk of our time playing good defense, and 2) us getting around them some of the time. This is to be expected. 973 played what I thought was the best defense of any team I watched this year - they were able to stifle not just mecanum opponents but others as well. Yes, it is true that they were not only defending our robot, but that is also to be expected.

I wouldn't put too much weight on any videos of us from the quarters and semis. We were trying to play zone defense, and just were not very good at it (as we never had practice). We were quick to let teams go. In the division finals and on we tried man to man, which really worked out infinitely better for us.

[sgreco]

Originally Posted by Tom Ore

Only 12 teams out of over 2,000 made it to Einstein this year. Lots of quality teams with 6WD and 8WD didn't make it either. A well done drivetrain of any type is just one part of a total robot / program that is required.

I agree and disagree. The 12 teams out of 2000 are not a simple random sample. The best teams make Einstein, and the best teams never have mechanum drives. The fact that the there is a consistent trend of simple 6WD's making Einstein and winning competitions speaks for itself. I don't think it's a coincidence by majority in numbers; it looks like a correlation to me.

(If someone has the number of mechanum teams in St. Louis, we could analyze whether the reality that they didn't make Einstein is statistically significant).

[JVN]

Originally Posted by sgreco

I agree and disagree. The 12 teams out of 2000 are not a simple random sample. The best teams make Einstein, and the best teams never have mechanum drives. The fact that the there is a consistent trend of simple 6WD's making Einstein and winning competitions speaks for itself.

Has anyone gone down the top 25 list and filled in the drivetrains? I'll start, but I don't know all of them:

254 - Skid Steer
111 - Skid Steer
1114 - Skid Steer
2016 - Skid Steer
217 - Skid Steer
987 - Skid Steer
148 - Skid Steer
1503 - Skid Steer
2056 - Skid Steer
233 - Skid Steer
67 - Skid Steer
33 - Skid Steer
1717 - Swerve
469 - Skid Steer
177 - Skid Steer
71 - Swerve
40 - Swerve
2054 - ???
118 - Skid Steer
330 - Skid Steer
16 - Swerve
51 - Slide Drive
27 - Skid Steer
2826 - ???
1538 - Skid Steer

Did I get all those right (off the top of my head)?

[safetycap'n111]

2826 had mechanum and drop down plaction wheels.

http://www.chiefdelphi.com/media/photos/36224

[Jared Russell]

2054 was skid steer.

2826 had an "octacanum" drive.

The rest look right.

[BrendanB]

Originally Posted by Ether

What do you think they did to make it so it couldn't be pushed easily?

They were able to lock their rollers with some special mods and with special programming they can realign/push back against defenders while retaining their position. I remember our driver bumping into them during a match with 6 plaction wheels and they didn't move.

Unfortunately for them they had mechanical/programming issues throughout the season but knowing this team they will be back and even tougher next year.

[JesseK]

I think the next trick to figuring out how complex drive trains should be is clarifying which of the D/T's on Einstein (or Top25) were:

• KOP (with perhaps sprocket gearing changes or different wheels, but all else the same)
• 1 or 2-speed
• Full-traction versus omni's on the corners
• Direct-Driven
• 4/6 motor
• etc

Speeds in high gear may be interesting to see, but really those are more about what a team's strategy is rather than 'best drive train'. I suspect we'd see a wide variety of skid steer designs in the top ranks.

[Mike Soukup]

Originally Posted by Chris is me

Do keep in mind though, the semifinals came entirely down to the minibot coin flip in match 1, and the finals were 2v3. While 254 / 111 / 973 was undoubtedly the better alliance, it was certainly not predetermined.

I know that Karthik's term "minibot coin flip" has become a popular way to describe the end game this year. I'm not a big fan of Logomotion's end game, and I think the description is true, to a point. But, eventually people have to recognize and appreciate greatness. 973 had the fastest minibot on Galileo and potentially the fastest minibot at Championship. 254 chose them to guarantee 1st place in the minibot race every match.

From now on, if you use the term "minibot coin flip" to describe our matches, know that our alliance was using a coin with two heads, we called heads every match, and won every toss.

[Chris is me]

Originally Posted by Mike Soukup

I know that Karthik's term "minibot coin flip" has become a popular way to describe the end game this year. I'm not a big fan of Logomotion's end game, and I think the description is true, to a point. But, eventually people have to recognize and appreciate greatness. 973 had the fastest minibot on Galileo and potentially the fastest minibot at Championship. 254 chose them to guarantee 1st place in the minibot race every match.

From now on, if you use the term "minibot coin flip" to describe our matches, know that our alliance was using a coin with two heads, we called heads every match, and won every toss.

I agree despite my post before - I meant that from a spectator point of view it didn't look obvious who the winner was. The average FIRSTer didn't know 973 had the world's fastest minibot, and that was what locked up the championship with a very strong alliance. A lot of people thought it was over when 254 picked 111 - but 973 was what firmly locked it up.

[JesseK]

It may have been a coin-flip-minibot championship competition ... but 973's deployment was nothing short of lengendary in swinging the probability their way. That thing was ramp-style with 2 naturally-articulating degrees of freedom and 1 driven degree of freedom. It wasn't going to miss the pole by even half a degree, most of the time. I talked to them in the inspection line on Wednesday, and you could tell they put a very large amount of time into that thing before Champs.

It also didn't hurt that they had fastest drive train on the field this year (from what I saw), which gave them the advantage in getting around defense to the towers. The 254/973/1868 drive train in and of itself is an engineering marvel. The fine details of it would be appreciated by most. It's designed up against the edge of constraints in many cases and isn't replicable by most teams (since it probably couldn't be done on a non-CNC mill).

[Peter Matteson]

Originally Posted by JesseK

I think the next trick to figuring out how complex drive trains should be is clarifying which of the D/T's on Einstein (or Top25) were:

• KOP (with perhaps sprocket gearing changes or different wheels, but all else the same)
• 1 or 2-speed
• Full-traction versus omni's on the corners
• Direct-Driven
• 4/6 motor
• etc

Speeds in high gear may be interesting to see, but really those are more about what a team's strategy is rather than 'best drive train'. I suspect we'd see a wide variety of skid steer designs in the top ranks.

177 used the latest revision on our 6wd that has gone through a lot of optimization over the last 6 years.

The stats:
4 CIMs
6x 4" AM performance wheels with roughtop tread.
AM shifter "guts" repackaged/repurposed and final ratios modified.
2 wheels are direct drive
~14 fps high gear
~5 fps low gear
Everything is packaged into a 2.5"x2.5" extrusion.

This year we used low gear so rarely that that our driver ocasionally forgot to shift when he got in a pushing match.

[Ether]

Originally Posted by Peter Matteson

6x 4" ... wheels

What was your rationale for the small wheels?

I'm thinking 1) less gear reduction necessary and 2) lower center of gravity

are there other reasons?

[apalrd]

Originally Posted by JesseK

...he 254/973/1868 drive train in and of itself is an engineering marvel. The fine details of it would be appreciated by most. It's designed up against the edge of constraints in many cases and isn't replicable by most teams (since it probably couldn't be done on a non-CNC mill).

We (33) built a live-axle drive inspired by team 254. We made bearing blocks and cam tensioners out of 1/4" plate and cut them on a waterjet, but the bearing blocks were seriously just three holes in a line and not hard to make by hand. The shafts were lathed by hand (we used keyed shafts since they were easier to machine), and the wheels, hubs, and transmission components all came from Andymark. If you simplify the design, it isn't hard to make.

The Cheesy Poofs transmission, on the other hand, is quite difficult to replicate as basically all of the gears are custom-made by them.

33 robot stats (We were on the top 25, so that qualifies us?)
-8 wheel (6" wheels) live-axle DualDrive combining Plaction, KOP, and Lunacy wheels. Two wheels are actuated by pneumatic pistons, automatically.
-2-speed, 4-CIM transmission (5.5 and 12 ft/sec)

[AdamHeard]

Originally Posted by Ether

What was your rationale for the small wheels?

I'm thinking 1) less gear reduction necessary and 2) lower center of gravity

are there other reasons?

The question I always ask the people at competitions who question are small wheels is, "Well, why do you use big wheels?".

Usually the answer is either they don't know, or they always have.

We use small wheels for a lot of reasons, but they mostly stem from two of ours teams primary design goals; less weight, and less friction.

Small wheels are physically smaller, which is less weight.
Small wheels require less torque to turn to achieve the same force on the ground, less force in the shafts/sprockets means smaller and lighter parts.
Small wheels need less reduction, which is both a direct decrease in weight, but also a decrease in friction losses as we can run less stages of gear reduction total.
Small wheels let you have a slightly longer wheelbase for all other factors the same.
Small wheels are cheaper for us to make, as it's a smaller diameter stock, and has much less wasted material.

Also, experimental data has shown that for rough top tread, smaller diameter wheels have more traction.

To summarize, teams with small wheels usually have done actual engineering and reasoning behind their wheel size choice. Many teams with larger wheels do not (although some do, and decide to use KOP or other COTS wheels of a larger size for some logical reasons (like 111)).