Because of the extremely low friction (mu=.06), the max acceleration a robot can experience is well below what the two motors can provide, so the max acceleration of a two/four motor drive are the same. HOWEVER, i think the 4 motor drive could have a much higher high speed. However, i don’t think you could readily attain it on the field because the field is actually pretty short.
Nor do I think you want to. Remember everyone that you’ll need to stop too, and that also requires traction :eek:
that is a very good point… while refs will be less ready to issue ramming penalties, deliberately ramming into the end wall at high speed is probably still discouraged.
My team considered using raisable and lowerable wheels as brakes, angled perpendicular to the direction of motion.
Not alloew according to <R06>
ROBOTs must use ROVER WHEELS (as supplied in the 2009 Kit Of Parts and/or their equivalent as provided by the supplying vendor) to provide traction between the ROBOT and the ARENA. Any number of ROVER WHEELS may be used. **The ROVER WHEELS must be used in a “normal” orientation (i.e. with the tread of the wheel in contact with the ground, with the axis of rotation parallel to the ground and penetrating the wheel hub). **No other forms of traction devices (wheels, tracks, legs, or other devices intended to provide traction) are permitted. The surface tread of the ROVER WHEELS may not be modified except through normal wear-and-tear. Specifically, the addition of cleats, studs, carved treads, alterations to the wheel profile, high-traction surface treatments, adhesive coatings, abrasive materials, and/or other attachments are prohibited. The intent of this rule is that the ROVER WHEELS be used in as close to their “out of the box” condition as possible, to provide the intended low-friction dynamic performance during the game
that… is a good point. i imagine our rules guru would have caught that, but thank you.
A wheel perpendicular to the direction of travel can meet all of the criteria of this rule. The tread of the wheel is contacting the ground and the wheel’s axis of rotation is parallel to the ground.
If having wheels skid sideways violated this rule, wouldn’t all teams violate it at some point during a match as they’re pushed around by their opponents?
This may be something that will get updated in future rule sets. I agree that as stated, it doesn’t forbid it, but i would be careful about designing a robot that way.
In his application, the wheels are purposely not in their “normal” orientation.
“normal” as specified only refers to vertical orientation, not which way it’s facing.
I do not believe that they meant “normal” when they say “normal”.
I beleive that they are using the word “normal” to mean perpendicular to the floor. As long as the rotational axis is parallel to the floor, then the wheel is being used in it’s “normal” position.
So if you made omni wheels out of these kit wheels that would be “normal” (since the use would be used as designed)?
note: I’m not suggesting anyone make omni wheels this year
Normal: yes, but it would violate other parts of that same rule (must-be-rover-wheels parts). at least, that’s the way i see it.
Because I’m too lazy to read through 4 pages of things I’m going to just go ahead and post what a mentor and I though up of as the reason for the two robots. We figured that since the fricitional force is the normal force times the coefficient of friction, then a heavier machine would generate more traction. But according to Newton’s First Law, an object in motion wants to stay in motion, and an object at rest wants to stay at rest. Therefore, for the heavier machine, the inertia of it is far larger than that of the lighter machine. We both felt that the four motor machine was heavier, but could not produce significantly more traction to counteract it’s inertia. Therefore the 2 motor machine accelerated faster only do to its smaller inertia.
While I’ll agree that deliberately ramming the end wall at high speed is hardly something to encourage (although there are bumpers to help absorb the impact) high speed ramming is quite legal this year. As is pinning a robot to the boards, sitting in the middle of the playing field and spinning around with your trailer behind you like a big hammer and all sorts of fun and crazy stuff. As the head ref said at kickoff “we expect there will be very few penalties this year”. That’s because there are very few rules!
Originally posted by feilmeier
Because I’m too lazy to read through 4 pages of things I’m going to just go ahead and post what a mentor and I though up…
You may wish to go back and read the posts, where you will find several excellent explanations of the physics at play. You will find that your suggested explanation is somewhat incomplete. In the future, should you wish to join a discussion, please be respectful of those who have already posted by taking the time to at least glance at what they have written.
It seemed to me like the four motor drive wasn’t that far behind. The difference in the times looked more or less neglegible. I’d wager that it could have gone either way, depending on the reaction times of the drivers, the charge of the batteries, and a multitude of other factors.
I think the point was that every drivetrain is going to be able to easily overcome the available traction, so torque is largely irrelevent this year.
Torque is extremely relevant, just not necessarily desired. You may find that lower torque drive trains work better, or there may be little difference in performance, but the important thing to remember is that available traction is the most limiting factor, not available torque.
Paul is right, being able to control acceleration is the key to this game, at least as far as mobility is concerned.
The demo at the kickoff where they drag raced the 2 robots is a great example of this. From the audio, you can hear that these robots were spinning their wheels under full thottle for about 7 seconds. Estimating the distance they both travelled in this time puts their approximate acceleration at ~.8ft/s^2. This is only about half of the theoretical maximum acceleration rate of 1.61. Why? because rapidly spinning the wheels (burning out) greatly reduces the coefficient of friction. It looks like it drops by ~50% or so in this case.
Thus, if you can figure out a good way to optimize your acceleration rate (AKA Traction Control), you will be able to easily out run anyone else who has not done so. Of course, you can only run until you get to a field boundary, but like with all games, getting there first is always a big advantage.
actually how does a motor on each wheel sound and maybe even an 8 wheel drive for the traction it would give you and a really big and slow gear ratio
No. The axis of rotation of some of the rollers will not be parallel to the ground.
I would tend to agree with the interpretation that “sideways” wheels are allowed, because the rules seem to clearly spell out their definition of “normal” in the parenthesis following the word.
Be very careful regarding how you interpret items in parenthesis within the rulebook. As was demonstrated by <R16> last year, statements within parenthesis are not part of the official rule.
I’m not saying “sideways” wheels are or are not allowed, only that statements in the rules within parenthesis should not be overly applied.