Winning Drive Train
 

so after a fun 2009 season, all the ideas about 4 wheel drive, 10 wheel drive, drive train with fans on it, and all that jazz.....what was the most effective drive train? what style had the most traction? Teams with the KOP 4 wheel drive train, what did you do to improve traction?

Re: Winning Drive Train
 

At one of the regionals i went to, the winners, used two fans on back corners of their robot, which seemed to be very effective. Our robot had 12 wheels, each side having 3 rows of 2. It is a matter of testing different wheel sets on the regolyth (or however you spell it), and seeing which wheel set was the most effective.

Re: Winning Drive Train
 

12! and how did you think you did as far as speed and traction?? lets say 4 wheel KOP? who won that shoving match?

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As far as I remember, we did pretty well with shoving and pinning. As far as speed and traction, both were average, but definitely could have been better.

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We had a 6-wheel 4WD system (the rear wheels were doubled up), and we had no trouble pushing anybody around. We also had great control.

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We did the swerve this year. It helped to prevent us from getting pinned. 2753 added the fan and it seemed to help them.

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Our team had 4 wheel drive for GSR and we added traction control for Atlanta. The traction control really helped. We had no problem pushing people around- http://www.thebluealliance.net/tbatv/match/2009cur_qm67

Re: Winning Drive Train
 

Anybody have anything quantitative to share? Anybody? Anybody? Bueller?

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We had the 6+1=3 drive. Normal mode was six driven wheels in tank mode. Switch to two front wheels and the third wheel mounted 90 degrees to the others, located just in front of the trailer hitch. The third wheel dropped down lifting the frame and the back four wheels up to put all the weight on the front two wheels. With the six wheels we could push most teams around. The three wheel drive allowed us to "twitch the hitch" and swing out of some pinning situations.

Re: Winning Drive Train
 

We used six wheel drive. Each side had two (doubled) back wheels and one front wheel. One CIM was driving each side through a SuperShifter (which, ironically, we never used).

We had a simple joystick ramp-up for a while, which worked okay. Towards the end of Atlanta, we developed an encoder-based traction control that worked great; its too bad it didn't see very many matches.

As a member of the programming team, it was difficult initially to convince the build team that more wheels would not actually improve traction. Then, they wanted to leave the front two wheels undriven (i.e. throwing away ~40% of our traction). Yay for physics!

Re: Winning Drive Train
 

This is not really quantitative, but....

The mentors on our team spent a lot of time watching the pushing matches trying to determine what drive train was the best.

Our final conclusion was reasonably simple: Whomever went into a pushing match with the most momentum initially won nearly all the time, regardless of their drive train.

We played with our gear ratios to improve our speed, and discussed changing our wheel distribution to change the weight on different wheels to improve turning, but in the end most teams proved that 4 wheels was just as good as any other option.

Some of the 'fastest' teams out there, like Hot, didn't even use traction control (at least they weren't using it in the Michigan regionals).

Re: Winning Drive Train
 

I just want an answer on why the mods let this thread happen for this game 2009 and traction shouldn't be in same conversation. Next 1251's robot was 4 WD with some traction control and a one speed custom gearbox about 7ish fps. Saying this we were just fine with traction for 2009 in fact it was one of our strong suits. We made the robot weight as close as possible to the limit 119.9 and had no problems basically moved every robot we needed too at the Fl regional except 233 who had an amazing traction control program. Saying all this we could still be pushed sideways if another team had momentum no matter what happened. The fans seemed to work well for some teams at gaining speed but not really for gaining a whole lot of traction. Other then that there was no real way to gain an advantage on traction this year.

Re: Winning Drive Train
 

Quick bit of Quantitative.

Wide stance 4 wheel steer crab. We initially geared for the same top speed as the "kit" and that was too slow (7fps I think). We got scored on a lot, and chased kit bots all over the field. (1st competition)

When we geared up to go faster (approximately 25% faster) (9-10 fps), we were able to score on "kit" chassis bots easier and able to run away and run down competitors better. This also reduced spin-out during launch, but a measured traction control was implemented shortly after that, so some bets are off. (additional competitions).

Observations. Wide stance bots were observably more manueverable (4x4 crab and fixed and 6x6 short stance) than long wheelbase 4x4, and even most long stance 6x6. Mathematically, wide stance, this gives better leverage at turning/swinging the trailer. It does however reduce straightline driving stability without Gyro-assistance.

Re: Winning Drive Train
 

Not sure where you got your information on the quote above, but I can assure you we had some version of traction control at all events we attended this season. I can only remember one occasion when we ran a match with it turned off, and that was b/c we attempted to try a new version that was alittle too slow on response.

With regards to drivetrain, we had a wide - 6 wheel drive system with the rear wheels raise about 1/16" to allow for some "rocking" between the front and rear wheels. Not sure what effect it had on the bot, I think it just made my counterpart feel better. There was no quantitative measurements taken to confirm or deny its effectiveness.

In terms of pushing power, once we finally worked out our traction control issues, we could wiggle our way out of most issues. But, we were not a pushing robot by any stretch of the imagination.

My thoughts were why push when you could be scoring??? I guess it worked out in the end :rolleyes:

Re: Winning Drive Train
 

We used the AM Toughbox kit transmissions on a wide 4-wheel drive, but changed out the stock gears. That changed the ratio on the trannys from about 12:1 to 5:1. Decreasing the torque made spinning out less likely, and made the robot quite a bit faster, although harder to control. It was good to be fast though:)

We weren't really too interested in pushing, our game was more scoring-oriented.

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We had a 9.8fps linkage drive where each wheel rotation point made 1 corner of a 18x18" square.

In hindsight, we should have made it wide-drive (rotation point rectangle of 29" x 18"). Not only would we still have had dynamic, on-demand centers of rotation for various wheel orientations, with a wider base we would have also had slightly more torque in turning the trailer at low speeds. It also would have simplified the frame design, heh.

Re: Winning Drive Train
 

One thing I noticed: 11/12 robot on Einstein were oriented with a 'wide' drivetrain. I don't know enough about all of these robots to tell how many had traction control, swerve, 4wd/6wd, fans, etc., but that would be a nice place to start if you want to determine the 'winning' drivetrain. If you're feeling ambitious, an analysis of the drivetrains on every robot in eliminations would be pretty cool, too.

I still think that good driving and strategy are way more important than drivetrain details, but that should be obvious.

Re: Winning Drive Train
 

Trust me, if i had the time i would. this game left me with my head spining.


well both 354 and 2681 had the KOP drive train thinking that over designing the drive train would kill us on time and weight. but if all that does not matter then, was having a traction control program the key to pushing people around and speed? or did teams see that having a wide base with 12+ wheels the way to go? i look at teams like 2753 and they fly with no problems. being the coach behind the glass, and involoved in first for 9 years, i just looked slow. im trying to see where i went wrong. both weighed 119.8 and weight was even through out the robot.

Re: Winning Drive Train
 

My apologies Adam. I had spoken with one of the volunteers from Lansing, and they told me that you weren't running traction control. Mea culpa.

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some of our mentors thought that having more contact points with the field (i.e. with the rover wheels) would provide less traction. so we went with a 4wd direct drive train holonomic drive train. we had an average speed and push power, and we had great manuverability. in our two regionals, we proved that our robot had power when we broke several strong supports with our drive train. in Atlant we changed our drive train to Direct Drive take steer with 1 joystick. the manuverability was decreased but the speed and power delivered was enhanced.

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I thought this was a good year to really nail that whole Ff=mu*Fn into people's head, but to get it past my kids we had to do some quicky tests to prove it. See attached data. :eek:

We took the kitbot stuff plus some junk around the shop and created a simple test bed to determine if more wheels would generate more force. We were less interested in pushing people around than we were in making the most of our acceleration (F=m*a). We used the kitbot frame and successively mounted wheels on one side, first 2, then 3, finally 4. We would have done more but that's all the wheels we had. We then placed this on a piece of the FRP that was spec'd and massed up the frame with stuff from around the shop. Each of these items was weighed individually (introduces error). We tried to keep the mass as close to the wheels as possible, but still needed to have a student support the outrigger side by a piece of rope with the goal being to keep the frame level (introduces more error). A fishing scale on the rope allowed us to back calculate out the load on the wheels by treating the assembly as a simply supported beam. (i.e. total mass - mass on rope = mass on wheels)

Once we know how much weight was on the wheels we moved the scale to the rear of the frame, in-line with the wheels. We applied power to the wheels and measured the force generated on the scale. Change # of wheels and repeat. Based upon the data gathered and the acknowledged crudeness of the testing we all quickly concluded that more wheels did not significantly add more force.

Based upon the test data we gathered I would say that anyway you could generate and additional lbf of thrust would be important. I was told that 45 & 469 could get 5lbf and ~4lbf respectively... That's 50-60% more thrust than me. :ahh:

"Foul, foul, I saw you use 6 wheels on your wide chassis at comps!" Read Chris Hibner's white paper, "Drive Train Basics (How to Be Sure Your Robot Will Turn)" It's not just about how much force, but where you put it sometimes that matters.

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Here is the data we took on our bot. We were using follower wheel traction control limiting the slip ratio to ~.2. The drawbar pull was measured using a fish scale (hand held) with both joysticks firewalled, while allowing the bot to slowly travel forward over the regolith. With just the wheels, we got around 18-20 lb.f on average. If we turned on the propeller propusion, we got 26-28 lb.f.

I won't say we got 8-10 lb. thrust from the props, I am guessing there were other factors involved. The voltage drop due to the propellers running may have made the traction control work better, or the airflow may have blown away the regolith dust as it was produced, increasing traction. I don't know. I am just reporting the raw numbers.

Re: Winning Drive Train
 

This year 816 used a Wide Based 6 Wheel Drive. We went with a wide base because it allowed us to have more of a "turret" effect with our robot while at rest and while moving. We found that a wide base was significantly more maneuverable at low speeds than a long base, and that the usual stability issues weren't a problem because of the trailer.

Our Drive train was geared for about 12fps which was more than fast enough for us throughout the season. It gave us enough speed to chase down almost any target and also helped us get out of quite a few jams. As far as pushing goes, we never had an issue pushing another robot when we really needed to. We didn't use traction control either to save valuable programming resources.

I don't have any test data on the drive, but if you're curious look at a video of us. Numerous people complemented us on our maneuverability throughout the season.

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We used fish scales to measure our pushing force. We had about 15 or so pounds with 6 wheel drop center tank drive. We added traction control that bumped us up to about 20 pounds and then we had 2 10" shrouded fans that each added another 4 pounds for a total of anywhere from 26-30 pounds of force at one time.

Re: Winning Drive Train
 

Did either 111 or 1717 have some sort of traction control?

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1717 did have traction control.

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In my opinion, the best drivetrain I saw this season was on team 743. I'm not sure on the specifics, but I know they had 14 wheels. Their defense knocked us out in semis at NY, and they made finals at both NY and CT. Watch their matches, they play great defense. Maybe someone from 743 could explain what set their drivetrain apart?

Re: Winning Drive Train
 

I am fairly certain that 111 had traction control. From what I saw, they have a sensor wheel for each of the swerve pods.

This year, I believe that our robot was one of the best pushing robots on the fields from what I saw of our matches. We didn't have traction control, and our robot is light. (115ish) I think that the reason we had more traction, was because this year we went with a normally extremely underpowered drive system. We did the calculations, and found that 1 CIM could provide more than enough power to the wheels to break into dynamic friction (without gear efficiency factored in). So we used 1 CIM, total, this lead us to have just enough power to accelerate at nearly the maximum rate, but also allowed us to never spin our wheels, meaning we had full traction, all the time.

Re: Winning Drive Train
 

Piper Robotics Team 1802, we had 16 wheels on a floating suspension and we could push 3 robots at a time into a corner and clear the field.

even though we didnt make it to the finals at our regional we had pretty solid pushing power

Re: Winning Drive Train
 

Any pics of the Drivetrain up close, this sounds very interesting. We could push 2 if we had momentum.

Re: Winning Drive Train
 

yeah its as my avatar but give me ur email and ill email u a few of those upclose pics

Re: Winning Drive Train
 

Here you go...

Re: Winning Drive Train
 

ok i sent the photos

Re: Winning Drive Train
 

What's traction control :rolleyes:

612 used a 4 wheel drive with front wheel steering. We don't have any quantitative analysis but on the field it was clear that our robot turned better than other robots who used skid steer (nothing wrong with skid steer, just saying on regolith with a trailer, front wheel drive turns better, on carpet different story).

Re: Winning Drive Train
 

2753, 25, 1902, 1251 all had what I considered the best drivetrains of the year. Solid pushing power with pretty decent speed on all bots. Personally, 25 used their drivetrain most effectively.

Re: Winning Drive Train
 

i think that the swerve drive on 111 was the best drive train for this years game because of how much easier it was for teams with swerve to avoid the defense. 111 won the championship and was able to shine every match because their effective swerve drive allowed them to never be shut down by defense like 67 was very often.

Re: Winning Drive Train
 

Our drivetrain this year worked surprisingly well.
At our best, we have pushed 3 robots at once.
It was just a modified, "wide ride", drop center, 6wd kitbot chassis with unmodified toughboxes and 1 CIM per side.
The only traction control we used, was a ramp up code, that increased the robots speed when moving from a stopped position.
But I think the reason it worked so well, was because of the weight distribution.
The weight on our robot was just slightly forward on the chassis, making us a front wheel drive which gave us greater maneuverability.
But if we got into a pushing match, the weight shifted to the back wheels.
Since our robot was able to rock back and forth, the force applied from our opponent pushing against us, actually lifted the front end of our chassis just a bit.
This in turn, applied downward force on our back wheels, helping us to "dig in" and gain more traction. Thus, we were able to use our opponents pushing for against them.
Now I will say, we did not in any way engineer our chassis to do this.
It was merely something we noticed happened while pushing another robot out of the way.
I don't have any math or statistics to back this up... but I will see if I can get some pictures of it up here soon.

Re: Winning Drive Train
 

Wow, all you guys were only able to push 3 robots sideways? We easily pushed 5, but never did so because we wanted to keep our alliance partners free....:rolleyes:

Actually, I'm on John with this one. Anecdotal evidence and stories don't mean anything; what I've learned from this thread so far is that, A) Every drive type so far is the best, or B) some people are exaggerating.

There is no need to toot your own horn, as most people just flat out won't believe you.

As for this game, i don't think a definitive answer to what drive test is best exists. 111 was an extremely good dumper with crab drive, but was it the crab that made them effective? I don't think so, I think 111 with a 6 would've been just as effective. Not to mention, even though 111 was extremely good, I think there are some other dumpers out there without crabs that are better in my opinion. 67 and 217 are tied in my head (along with a few others) for being the best robots this year, and both showed they were extremely manueverable with a wide 6 wheel. I imagine they drove that 6 wheel better than a lot of teams drove crabs.



In the end, people can throw all the stories at me they want, but I'm never going to let mere stories convince me physics is wrong.

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Wildstang is a great team with one of the most amazing drivetrains ever seen to first. Their drivetrain definitely helped them win, .(obviously being successful is a combination of doing many things well) but I'm going to argue that more important than that was their ability to hold almost 40 and dump them all out really fast. I think that was the biggest reason they won in Atlanta.

Re: Winning Drive Train
 

Yes, Wildstang had traction control. We used a manufactured wheel with foam as the tread to reduce forces to an absolute minimum. This wheel, on the same axle as the drive wheel, allowed us to compare the two to determine slipping of the drive wheel.
We prototyped several drives and settled on crab again this year. It proved in testing to be more effective in handling the trailer. We found, as many of you did, that the trailer shifted the center of rotation to somewhere outside of the robot. By using crab, we could then put that center where ever we needed it. Crab also allowed us to skid steer when going fast and control the robot when we needed to dump. It is important to note that the bumper rules also played into this. The six inch minimum segment length meant that we could not have a ball pickup that was the entire width of the robot. Since the pickup opening was limited to 26 inches, there was room for crab modules at each corner without sacrificing rapid pickup.
BTW, this is called crab drive because it mimics the way crabs move across the beach. The term has been in use on camera pedastels since the dawn of TV.

Steven,
We could only hold 25 or so, but thanks for the kinds words.

Re: Winning Drive Train
 

Well, I have some info/data about our drive train this year.

It was 4 wheel, linked left/right power and steering crab. Wide side "forward".

It seems that this year wide drive robots had a better time getting around, as well as an easier time not getting pinned.

The crab was really nice for pinning, as well as maneuvering out of tight situations.

We did some tests with a fish scale and determined that the drivetrain itself (120 lb + 15 bumper + 12 battery) can give ~9-10 kg of thrust.

We also had fans on our robot. Using a different setup, we tested each fan to give 2 kg of thrust, without a shroud. Two fans -> 4 kg. Each fan was powered by a CIM directly. In the end, after efficiency loss, the fans together probably output 3-3.5 kg, or an extra ~30-40% thrust. It was noticeable on the field, at least from a driver standpoint. First, it made acceleration much faster. Second it made it easier to stay in contact with a robot once contact is made. Third it makes it easier to hold robots once you get them to a wall.

That's all I have. I hope that's what you were looking for.

Re: Winning Drive Train
 

I agree with Adam. The other question (which hasn't been fully defined) is, Best at what? Offense, defense, pinning, avoiding pinning, etc. Sure, you can build a great offensive drivetrain, but somebody with a great defensive drivetrain may be able to beat you. There is a difference, I'd say.

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WOW! :yikes: thats for that was alot for me to read on my phone! i had to wait till i came home, but thanks!!!

are we talking about dead stop pushing or full speed ramming? because i can push robots around when at full speed 100% traction.

The problem: The Feild + KOP wheels... what was the best solution? it dosent matter about offensive or devensive. what matters is out of all the different combonations teams came up with, which concept was the most effective? the fan? the 100+ wheels? the programming? 4 wheel tank 1 CIM? 2 CIM? Wide base ?narrow base? etc...
i look at my team with 4 wheel tank 2 ONE CIM each side with KOP gear boxs at 119.8lbs and no traction programming i say this was an avg drive train. not a winning one.
you may be right when you look at playing on carpet, but 2009 was a little different.

Re: Winning Drive Train
 

Look at 330's drivetrain. Defense was their specialty, yet they didn't often pin and liked to score a lot. 6WD, very narrow, sort-of crab, traction controlled. Effective? Maybe. Most effective? Probably not, depending on your definition of most effective. Decent all-around, but not outstanding at any one thing.

And you STILL haven't defined "most effective". Most effective at what?

And with all those combinations you list, you may be right playing on carpet, but 2009 was a little different.

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This is the most underlooked post in the whole thread. I think it is clear that wide drivetrains were most effective, because they facilitated power dumper robots, which also proved to be among the most effective. Traction control, number of wheels, additional fans, swerve drive, etc. all played into helping teams win, but ultimately the combination of a wide robot with a fast unloading mechanism was deadly. As long as the drivetrain was controllable enough to pick up balls, and eventually pin, that was all that was needed to win. Optionally, playing 'run-away' defense, and combatting against that, was aided by additional features, but was an edge case because usually robots could and would get pinned.

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I love how a question asking what the most effective mechanisms were turns into "talk about what my team did" time.

Simple wins. Always. This is the year that convinced me of that (finally realized which parts of design are OK to think inside the proven box...). You probably won't see any more crabs out of me.

Looking at images of the total winning teams, I'm seeing a trend in simple drive train. This is the first year in a few that we've had a crab make it to the finals on Einstein, and come out on top. Two thirds of the winning alliance was 6 wheel drive.

Simple rules the day. Always.

Re: Winning Drive Train
 

OK.

We drove wide, skid steer with a purposely shortened (14" center to center) wheelbase so that we would have less scrubbing while turning. With our CG just forward of the rear set of wheels this gave us excellent turning and control without reducing the standard ~15 LBf thrust allowed by the rover wheel CoF. Interestingly enough, we're not tippy either ... although I wasn't to worried about tipping with the low CoF this year.

We used a single CIM on each side, directly (through a toughbox) driving the rear wheels and chained to the front wheels. This gave us a safety margin should we throw a chain (not expected ... but one of the highest DFMEA values)

Additionally we gave our driver the ability to control the power curve to the wheels and thrust limiting, this allowed him to control wheel slippage as needed.

Next we added two 16" triblade propellers which added ~4.5 LBf each. These were reversable (although less efficient in reverse) and assisted us in direct line (forward and reverse) as well as turning. With this extra thrust we would overcome the trailers friction, thus the tail (trailer) never wagged the dog (robot).

While thrust for both the propellers and drivetrain were driven off the same joystick, they had different power curves. This allowed us to tune each independently.

The above gave us what we were looking for, in our strategy, The ability to get off the line quickly and the ability to pin (in both autonomous and teleop).

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That's a neat feature of this year's game...with limited traction, we decided early on to not spend much time on the drivetrain, but put our effort into making the robot pick up balls quickly and unload them quickly.

Some qualitative data....we used the kit drivetrain, completely, one CIM per side, toughboxes, two wheels per side, kit sprockets, bearings, axles, spacers, and chain. But our driver noted after watching videos of our robot in action: "Wow, we're slow!" so we ordered some 20 tooth sprockets to replace the kit 15 tooth transmission sprockets, and made the robot faster in Atlanta.

Re: Winning Drive Train
 

In the course of testing, we found that the difference between the static and dynamic coefficients of friction between any given rover wheel and the regolith was about 20%. However, the difference between clean and dirty (covered with FRP dust) wheels was on the order of 40-50%. I believe that this accounts for some of the discrepancies between the published CoFs and values that multiple teams found empirically in the first week of build.

So while we had some sort of software traction control implemented at all three of our events this season, it was our "mechanical" traction control that helped us the most. Each of our four drive wheels had a paintbrush mounted against it at the top of its rotation. These brushes did a superb job of keeping our wheels clean during and in between matches, and spared us the chore of having to diligently clean our wheels by hand (though we did need to periodically clean out the brushes - you wouldn't believe how much dust they would accumulate). As a result, we were typically a very slippery target for opposing robots (look at our DPR stats this season, although in Philly a couple of problems made us a sitting duck once or twice). Multiple other teams commented on our ability to break out of pins, and it was only when it was 2-on-1 that we were really immobilized.

However, it is interesting to note that our choice of wheelbase meant that despite our tractive advantages, we weren't a very good pinning bot. We were a "skinny" bot because of dimensions of our scoring system, and we had a 4WD setup on a shortened wheelbase towards the rear of our machine.

Top view:
As a result, if we were pinning another bot, it was easy to turn us because of the distance between our robot front and our wheels (our chasis acted like a long lever). Thus our pins were usually not hard to get out of.

Lastly, we found that TOO much traction control was not always a good thing. Our initial software (used in San Diego and Philadelphia) fought to keep the bot on course and slip-free, making drifting and the effective use of the trailer's momentum to quickly turn more difficult. In Atlanta, we toned it back just to acceleration limiting, and our driver responded with our best robot performance (despite the outcome) of the year.

Re: Winning Drive Train
 

More wheel's didn't give move friction. You spread out the weight across the wheels. Traction control was a way to get the theoretical maximum acceleration. we did a crab/swerve drive.

Re: Winning Drive Train
 

I will counter this and say that this year, more wheels did actually return more traction. I know that physics says that Friction force = coefficent*normal force. However, this is for a perfectly ideal surface. This year, I witnessed teams with 8 wheels either in a dually 4wd configuration or in a standard 8wd configuration, have more traction than a similar 4wd or 6wd drivetrain. Our alliance partner at Peachtree utilized a dually 4wd layout with 8 total wheels, and they accelerated faster than us, with 6wd plus fans and follower wheel based traction control.

If I were to redesign a drivetrain for this year, I would do either a 4wd or 6wd layout but with dually wheels, and have dual ducted fans as well.

Re: Winning Drive Train
 

you witnessed it? or you measured the actual amount of force each drive was making, and compared them?

Re: Winning Drive Train
 

Although, I do not disagree with your general premise of simple wins, there has been a swerve in the finals of Einstein each of the past three years and two of them have been on the winning alliance. Having said that, that means that 3/36 teams on Einstein the past three years have had swerve drive and 2/9 of the Champs winners, simpler drive systems still far outnumber the more complex ones.

148 had a swerve last year although it wasn't the same as what teams typically think of as crab. 71 made it to the Einstein finals in 2007, although they did not win.

Re: Winning Drive Train
 

These are all cases where it's really hard to separate cause and effect.

In 07, assuming the rest of the robot was the same, 71 probably would've had equal odds of making einstein if they had gone with simpler drive.

In 08, even though the crab was much more a part of their strategy than in 71's case, 148 probably had similar chances of making Einstein with a small, fast 4/6wd with ackerman steering (or just straight tank).

Now, in terms of comparing acceleration, traction, etc... You CAN'T do it by watching video or matches. period. There are too many variables that you can't account for. Different drivers, different software, etc...

If you want to make any case for what driver pushed harder or steered better, you have to have some sort of data to back it up. The 4wd team XXX had pulled with 12 lbs of force and our 72 wheel drive pulled with 12.4 pounds. Our 4wd turned at 176 degrees/second with a trailer and their 72 wheel turned with 165 degrees/second.

Now, I'm pretty much 100% certain no one has done this across multiple teams, and we can't trust numbers from different teams to compare (differences in measuring equipment and floor would skew it too much), so we can't really go around making these claims can we.

Re: Winning Drive Train
 

I believe the teams won more due to the fact that their drivers and strategies used the crab/swerve to the best of their abilities. Rather than using crab to drive around and strafe like typical bots did, they found a way to use the uniqueness of their drive train to perform a unique task.

148 in 2008 played ridiculous defense and could get through tough spots that others couldn't. That was key in most of their games on Galileo and Einstein. 111 in 2009 immediately strafed to pin an opponent's bot AND position their own bot for top loading. Al mentioned the dynamic centers of rotation (in the crab/swerve thread) that all crab drive trains discovered this year, which was key to their success in this maneuver -- they wouldn't have been as effective in that autonomous strategy with skid steer.

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I disagree. The reason 111 was such a good dumper was because of swerve; it simply was not possible to lock them down 1 on 1. They were also able to slide sideways and keep the front of their robot oriented toward the trailer. If there was any one thing I could have changed about our robot this year, it would have been the addition of swerve drive (besides, we actually came at weight this year...)

If you watch 1717's videos, they had a trick where they could go face to face with another robot, then slide around to hit them on the side. This is especially useful because for robots like ours and 1717, if we get you on the side we will fill your trailer. Unless you have fans or swerve, it simply is not possible to break out of one of us pushing the side before we empty our screw into the trailer.

Re: Winning Drive Train
 

we just used 4wd tank steer.....

we seemed to be able to push people around with no problems....

though, I definately felt teams with other drivetrains(fans,swerve..etc..) had more of an advantage........

Re: Winning Drive Train
 

I've been following this thread and have notice that, as Adam and JVN pointed out, a lot of this is speculative and isn't being backed up by actual numbers. Allow me to break tradition and share some of our testing methods and summarized results...

When we first started brainstorming we we very focused around being as simple and easy to repair as possible. We wanted no headaches at competition. Therefore we couldn't find a good way of justifying investing the time in developing and producing a crab/swerve drive. INHO those kind of systems need to be developed over the off-season not in the time precious 6 week build season. So the first question was: 4 or 6 axle drive...

4 axle vs. 6 axle Testing
We took our 2008 robot, made rover wheel hubs to fit its 7/16" hex shafts. This became our test platform since we could test 6 axles or remove the center wheels and test 4 axles.

We set up a 8' x 24' FRP track. We did a few different tests:
A) Straight Tests
B) Turning Tests
C) Push/Pinning Testing

We ran the robot down the 24' end of the FRP 10 times, each time on a different area so the FRP wouldn't wear in and give us more traction. We timed each run at full speed so theoretically the wheel slip time would be the same. We found that the straight-away times between 4 and 6 wheels were pretty much the same.

For our turning tests we would go from a straight away, into a turn and time how long it took to make a 180 degree turn. Then we would time how long it took for the driver to regain control in a straight-away after making the turn. We found that the 6 axle version made the turns quicker, but took longer to regain control after making the turn. The 4 axle version made much wider turns, but took no time to regain control after making the turn.

For our Push/Pinning Test we moved the FRP over a large piece of carpet. We set up a wall made of tables. We put our 2008 robot (with rover wheels) in different configurations on the wall (front two wheels on carpet, one side of wheels on the carpet, etc). This wasn't so much of an objective test as much as it was a scenario test... We found that the rocking motion of the 6 axle robot hurt it in pinning situations, especially when the robot was pinned front or back against the wall. The rocking motion meant that there were times when you would potentially have no wheels on the carpet and therefore lose any chance you had at getting out of a pin.

This led us to go with a 4 axle robot. Then came the question of how many wheels to use....

Breaking Force Testing for Multi Wheel Axles
We actually did push/pull/breaking force tests for the rover wheels on FRP. We created a jig that allows us to test 1, 2, 3, 4, 5 and even 6 wheels. We locked the wheels in place so we could test the breaking force the jig. We weighed the jig down with ~40lbs (the amount of weight per axle on a 4WD machine). We dragged the fixture with a fish scale across a section of FRP. The weight measured at the point where the wheels started dragging would be the breaking force.

We found that each wheel added to the fixture greatly reduced our breaking force. 2 wheels cut our breaking force in about half. After seeing it continue to drop after testing 3 wheels and 4 wheels we decided to stop adding more wheels since it was obvious that more wheels per axle meant reducing our breaking force.

After further research on running multiple wheels per axle it turns out that Trucks use them to reduce the load per wheel, not for traction purposes. Think about it... Semi-trucks are the most common vehicle for running 'dualies'. This is because each wheel on the axle reduces the load on the wheel. And if you notice, they're typically only running dualies on the trailer end (where a vast majority of the weight it located) of the truck because they want the traction on the cab.

This is what led us to going with a 4 axle, 4 wheel robot.

Re: Winning Drive Train
 

Thanks!

We have a not very old tradition of sharing most of this type of data during build season....and we haven't found any down side to it yet.... :)

Re: Winning Drive Train
 

3who?

Re: Winning Drive Train
 

I didn't mean of us not sharing it period, but of breaking tradition in this thread in actually using test data instead of saying 'well I saw team XXXX push every robot collectively at the ABCDE Regional' or 'Team XXX was better than Team YYY because a friend of a friend's girlfriend's sister's brother's nephew said so...':rolleyes:

Not that I'm advocating that we had the best drivetrain, because I don't think we did... To be honest the best drivetrain was different from team to team because each team played this game their own way....

Re: Winning Drive Train
 

Adam, on Raptor's DT, did you have the two rear sets of wheels closer to each other than the front set? I saw this on a lot of the 6wd set ups and was wondering if you could evaluate and explain the advantage of the set up as a posed to a 6wd with equally spaced wheels.

O-O---O

Was this basically creating the effect of a 6wd with a drop center for turning purposes?

Re: Winning Drive Train
 

you know... those beach city robot kids... haha

Re: Winning Drive Train
 

4 rear wheels close to rear of robot, with weight over them most of the time, makes for very easy steering with the trailer.

Re: Winning Drive Train
 

squirrel nailed it.

We ended up with a wheelbase about 36" wide and 9" long. Mathematically this turned better, but we did no testing to confirm such results.

We did however try removing the center wheel, which the driver complained was too slow at turning.

Re: Winning Drive Train
 

We did no testing, no precision drilling, just 2 holes on the ends of 2 pieces of box tubing, stuck an axle through them, wide drive base, the widest footprint and longest footprint we could give ourselves.

And it worked awesome.

Lol.

Re: Winning Drive Train
 

I know its probably highly unlikely, but did anyone get to measure pushing/pulling forces on new FRP materials like on Einstein and compare the numbers to heavily worn FRP? It would be interesting to see how much the results differed from FRP dust and lots of other factors. Significant addition in traction? No effect at all?

Re: Winning Drive Train
 

You will note that on page 2 of this 5 page thread, at least one team did exactly that, post actual test methodology, along with resulting data.:rolleyes:

Re: Winning Drive Train
 

Did anyone run these tests on FRP on top of carpet like the real field is (at full robot weight)?

Re: Winning Drive Train
 

Our tests were run with the complete robot on frp over carpet so they were identical conditions to the field.

Re: Winning Drive Train
 

to me it seemed like without traction control then nobody had much advantage with drivetrains, except the swerve drive's were pretty slick.

i also saw some of the most creative and out there ones seemed to be less effective, vs regular tank drive.

Re: Winning Drive Train
 

For all it's simplicity, regular tank drive is efficient and effective.

Re: Winning Drive Train
 

Well I could go on for a few pages on this one...but I will spare you all.

It seems to me in the few years I have been doing this that what works for each team is different. In general, if you do the simplest thing you feel you can get away with you can spend your time working on the details that make it work really well rather than just making it work at all.

For some teams this means building different things. To us, it meant using kitbot and kit transmissions and then spending our effort on follower wheels and traction control.

To an amazing team like 111, their incredible swerve drive is a given, and they still can spend their effort on just making it work well.

My hat is off to the teams that figured out the drive challenge this year. There were many paths to success, and you can find inspiration in looking at how some of the incredible teams in first got there.

Just remember that you can get just as much inspiration from making a simple system's details work really well as you can from just making a complex system work...

Re: Winning Drive Train
 

I talked to people on 1218 and their driver commented that the unworn Regolith behaved completely differently than on the Archimedes field.

Re: Winning Drive Train
 

Akash,
After several months of practice and several events, I have come to the conclusion that the point of contact with the floor of any wheel is so small that other factors seem to have little effect. I have seen small spots on the floor worn through the surface or have the high spots removed by repeated slipping in one spot. However, the chance of that small spot and your wheel meeting for increased friction is very small and only lasts a fraction of a second. In practice (at our shop) our wheels were picking up all kinds of debris from the floor including what appeared to be wax, to the point they were completely coated. At events, the field people were cleaning the floor at regular intervals to keep the grit to a minimum and clear the floor of the normal hardware, wire ties and insulation from wire. I examined several of these pads after a cleaning and found that same waxy type of coating and extreme amounts of dirt and dust. Anyone who was near the field knows that they were breathing this fine dust and it covered my laptop at the regionals where I inspected everyday. The good news is that every robot that practiced or played one match came off the field with significantly cleaner wheels than when they started. As inspectors we feared we would be making teams sand or clean wheels on a regular basis. That fear was unfounded during the first week regionals. I have a bag of sand paper and sanding blocks at home that went unused.
When we tested pulling force on our field there was no perceptible change from the first day to ship. And the same was true at several places on the floor. I would suspected that humidity might have made a difference but it turns out that the surface is sealed with an overcoat of resin.

Re: Winning Drive Train
 

StealthGuardian,

Very interested to have our student learn you floating wheel design. Can you post a few picture of wheel design on web?

Dean