# Scientific Traction Testing at Nationals

For everyone who is tired of hearing unquantifyable or unrealistic boasts of robot pulling power, Team 180 is bringing a traction tester to EPCOT. It is basically a 4ft x 5ft wood floor with carpet glued down and a bracket holding a spring scale and pulley. You can bring your robot by, set it down, we’ll have some spectra so you can figure out where you want to tie your robot to the pulley, tether up and away you go. We should be able to measure pulling force from 0 - 400lbs. We will even have prizes for best pulling robot. You’re welcome to use the table if you want to tweak your traction. Any suggestions on prizes that would entice people to come by and try it out?

Will you have goals available for the teams that lift the goals to gain extra traction?

We had not planned on it because of the size of platform that will require. From the simple test you should be able to know what sort of coefficent of friction you have. You should be able to multiply that by your robot weight + the goal weight you think you are carrying to get your true thrust with goals (at least you’ll be in the ballpark).

Get some paper, make a little seal, and copy it about 100 times or so on a copier.

Bring it down to the competition with your platform, and award each team with a “Team 180 Traction Inspected” seal. Fill it out with the traction rating and the team number.

Great idea! In order to get the downward goal force right, you could have a couple of hefty springs that can be attached to the robot, and vary the tension in them depending on how much down force a team expects. Although the math route that you described would do the trick more safely.

Another idea that just popped into my head - our team has a partial goal that we brought to LSR, made to the right specs, but with only two bars. Something like that could be easily loaded down with weight to give a rough estimate of goal-added traction.

Also, be careful about your carpet. If I were you, I’d bring at least one extra slab of carpet - it was being ripped and burned by many teams at many regionals.

Fantastic idea! I can’t wait to see it work!

to bad you guys couldn’t bring that to the KSC. We won’t be at the nationals but would of love to have a pull off.

Like the battle we did in one of the matches at KSC

Good luck team 180 my money is on you guys. just get the gear to work good.

Wow…no one told me about this big plan…oh well…great idea, Mr. Jones! I really like the whole sticker approval deal. You can buy the sticker sheets anywhere. ~Angela

maybe we can put little slips of paper that say “Inspected by 180” in the pockets of all the robots =-]

George
SPAM
Team 180

This is a great idea!

If someone has a spare set of free weights to add to your experimental set up, you could use those to simulate the added weight of goals for the robots that lift goals for added traction. That might be easier to use (and calibrate) than a set of springs. Just find out how much weight of the goal is lifted by the robot (for example, we know we transfer about 90 pounds of the weight of the goal to our robot when we pick it up, the rest of the weight stays on the “outboard” goal wheels), and stack that weight on the robot before the traction test.

-dave

I know not with what weapons World War III will be fought, but World War IV will be fought with sticks and stones.
– Albert Einstein

Ok, We’ll try to bring some weights so we can simulate lifting goals. I think I am going to have to order a stronger scale. We will also make the platform so if the carpet on one end gets torn up we can turn it around and use fresh carpet on the other end. We will also print up some official “TEAM 180 Certified Thrust” certificates which tell exactly how much a team can pull. That way when your strategy guys are talking to other teams and they say they can pull Sooooooo much, don’t bank on it unless they have one of our certificates. We will also have some prizes for best pulling robot and maybe even best “wolf in sheep’s clothing 'bot” if your traction surprises us.

Sorry to hear Team 61 won’t be at Nat’s. You were the only guys we deliberately conceded a goal to at KSC. That grabber on a cable was brutal and you guys had excellent traction. I still can’t figure out how you kept those belts on though.

And BTW, the gearboxes will be rebuilt and beefed up for Nat’s.

James
Engineer/Coach
Team 180 SPAM

I’ve always encouraged teams to do carpet testing on their robot. Not only would they learn more about traction and weight distribution, they will also get to see if their wheels/treads are going to damage the carpets at the actual competition.

So, I am wondering if you guys can show teams how to build such a traction tester, so each team can build one easily at home.

It will be really cool if every teams have one of these traction tester at home, so they can try out different wheels material, different weight distribution, and different shape of robot .

I suppose it’s really easy for teams to just come up with one themselves, but why not help them out by drawing a plan for them?

And, eventually, we can come up with a bunch of numbers from each team for the coefficient of friction of the material they are using on the wheels/treads. With enough testing, we can even figure out the best material for robots using 4 wheels, 6 wheels, treads, etc, without damaging the carpet.

This is great stuff for teaching teams about drive system!

Thanks a million!

Actually Ken, I had planned to put out a white paper in the off season that would list various drive systems (wheelchair wheels, timing belt etc) and their coefficient of friction based on data collected at Nationals. Most teams really have no idea what sort of drivetain loads to expect and I think this will help. Did I mention that the only condition for using the table was that we get to see how much you pull? Obviously if someone has some supersecret traction surface that they think out pulls everyone else (we’ll let you know if it does) I’ll agree not to publish that data.

As far as a standard test set up, the most basic is just some rope to tie to the robot and a spring scale plus a cross bar for students to hold on to. Our setup is not going to be very elaborate. I can post some pics when it’s done.

James
Engineer/Coach
Team 180 SPAM

This idea just popped into my mind… Not sure how well this will work, but…

How about we convince FIRST to use this at each competition, during inspections, where teams have to put their robot on, run it on a traction tester, and see if it rip off the carpet.

There were quite some confusion on the yahoo board regarding damaging the playing field by damaging carpets… So, why not convince FIRST to adapt your idea, and put a tester at each regional, where teams can only pass inspection if they put the robot on the tester, run it against the wall, and see if it rip apart the carpet.

Not only would this convince teams to test their drive train before competition, it would also motivate teams to use a systematic way to test and improve their drive train. I wonder how well this will work out? Will FIRST have enough resourcse to make it happen at each competition?

How would we suggest this sort of thing to FIRST?

If FIRST had established a “standard carpet damage test” at the beginning of the season (which I wish they had) I would support it. Halfway through the season I’m not in favor of adding new test/requirements. Quite frankly I think FIRST should have either come up with a standard test or made the field carpet much easier to replace. The fact is the carpet often gets damaged from parts of the robot nobody ever intended to touch the carpet. Repairing the carpet during the day and replacing it every night would make everbody alot less sensitive to the damage issue.

I agree in the future first needs to define standard tests to establish objective ways to evaluate their subjective rules (carpet damage, entanglement etc.) I hope in the future they don’t repeat the nebulous requirements put on this year’s bots. It really gives teams that are willing to push the rules an advantage since I don’t see many teams being asked to redesign things. But this is another thread I guess.

James
Engineer/Coach
Team 180 SPAM

FIRST like to make rules then change them at the end. The tether rule hurt alot of teams. becuase the way they told us what would work and what won’t work. an at the competition they threw it out the door.

same way about the rug. It was clear that Heat wave machine would rip the rug the way they planted themself to the rug but they got away with it even after they rip the rug.

*Originally posted by JamesJones *
**If FIRST had established a “standard carpet damage test” at the beginning of the season (which I wish they had) I would support it. Halfway through the season I’m not in favor of adding new test/requirements. Quite frankly I think FIRST should have either come up with a standard test or made the field carpet much easier to replace. The fact is the carpet often gets damaged from parts of the robot nobody ever intended to touch the carpet. Repairing the carpet during the day and replacing it every night would make everbody alot less sensitive to the damage issue.

James
Engineer/Coach
Team 180 SPAM **

Yup! I totally didn’t meant to convice FIRST to use this test this year. I really think that if we can help FIRST establish different grounds of different rulings, such as entanglement and damaging the carpet, FIRST will have a much easier time in the future when dealing with clarification of rules.

If we put enough thoughts in this, and get this traction tester working really well (which I think team 180 already did that), then there should be a good chance for FIRST to do this in future competition. Should be easy to implement and useful for inspections. It’s pretty much a sure way to tell if robots are going to damage the carpet. Any other damages that’s going to occur during matches, I am pretty sure they are not likely to happen.

And, I don’t think FIRST “like” to change rules to mess up teams… There must be some sort of reason why they HAVE to change it… Even though I don’t agree with some of the changes in ruling, I don’t think we should be too harsh and keep telling FIRST what they are doing is wrong…

Save these up, talk to other teams to establish some general issues we want to talk to FIRST about, and if we get enough people to agree with us, FIRST will do the changes. This is what’s great about FIRST. Over the years FIRST have improved so much because how much they listen to teams about these sort of things.

I guess I’m the one who will end up manning the traction test in the pit since James will be on stage most of the time. A couple things for teams to remember:

(1) Traction and Pulling/Pushing power are not the same. If you have plenty of traction but aren’t geared right or don’t have enough motor power behind you, your treads won’t slip but your motors will stall and backdrive in a pushing contest, causing them to burn up or fuses and breakers to blow and lots of other unpleasent problems.

(2) Traction without power can be a good thing - if you can apply a brake and cause the other guy’s motors to stall and burn up.

Sounds like we have plenty of interest - We’ll try to put together a test set-up that is as quantifiable as possible for both traction and pulling/pushing power.

BTW - I ran some quick calcs relative to breaking a 1000# rated cable (see another thread) - you could certainly generate more than enough impact load - it’s a function of stiffness and velocity, not power or traction so that’s not really a good metric.

hey i think that the traction test would be a great idea. I dont think our team really knows really how much traction we have. Also if you did the test on the practice day then if some teams wanted to try to improve their own traction they would have a little time. if you need any help making stickers or whatever just let me know. im on team 234.

jessi amt

Count team 45 in for a traction test… we might do pretty well.

We would especially be interested in a loaded test, since we transfer the weight of a goal to our robot.

Andy B.