Top speed?
 

Iʻve done a search in the forums and looked through the manual, but canʻt find any rules regarding a top speed for the robot. Just want to make sure Iʻm not missing anything. So is there a top speed for the robot this year? I donʻt think I remember any in past years either.

Re: Top speed?
 

There is no speed limit, provided you steer clear of <G37>. Obviously, the laws of physics also want to have a word with you before you embark upon your 50 fps drivetrain.

Re: Top speed?
 

Speed of light is the fundamental limitation. Sonic booms would probably be discouraged. Most likely, safety will be the determining factor - a 20 ft/sec robot may be deemed unsafe by the referees if it behaves as if out-of-control.

Maybe this year a speed limit will be established, which would be an "interesting" development for the program. Radar guns!!!:ahh:

Re: Top speed?
 

cool, thanks!

Re: Top speed?
 

Restrictor plates, just like NASCAR

.....look it up :)

Re: Top speed?
 

Another way to get "governors" to FIRST competitions?

Re: Top speed?
 

There could be a limit on the speed but I doubt that any robot could hit any dangerous top speeds on the short course.

Re: Top speed?
 

Good luck trying to turn with a 30 fps drivetrain...

Re: Top speed?
 

i think the general speed limit will be limited by the laws or relativity :)
299 792 458 m / s that should be a general limit to how fast you can travel in the event (or at any time lol)

Re: Top speed?
 

Like everyone above me said, there is no SET limit.

But most folks can't handle a drive train that's faster than about 15 f/s.

Steering becomes really uncontrollable, not to mention the increased likelihood that you'll slam into the opposing player station wall, or the center field element. Good luck with whatever you choose!

Re: Top speed?
 

Maybe this is the year that automotive style turning, with a differential, makes sense. It would certainly allow high turning speeds and easier turns for the driver to coordinate.

As to the original question, I think the general consensus is that after about 18 FPS a typical robot becomes very difficult to control and a real pig in a turn. Things like trick wheels, multiple motor drive trains, shifting gear boxes and real sharp PID loops could probably make 25 fps or higher controllable and useful, although at that speed your crossing the field very very quickly. It's an awful lot of design trade offs for that speed. But maybe thats worth it to you. If it's ever been worth it, this would be the year. I'd love to see a robot 'hotrod' that just throws every thing it has into a drive train of epic proportions.

-Andy A.

Re: Top speed?
 

Did anyone say drift control?

Re: Top speed?
 

We are definetly considering an automotive inspired steering system, but trying not to fall into making a go-cart, was more just curious for other teams sake, but I donʻt think we are going to put that much into speed...but who knows!

Re: Top speed?
 

No, they said high speed....which is generally a different subject....

(unless you're on a dirt track)

Re: Top speed?
 

hehehe ... make way for sprint cars ... erm robots :D

Seriously though, the top speed allowed is the speed in which you can still control yout 'bot.

Anything beyond that will be 'unsafe'.

This may also be the year for suction cups on your OI, as I can see the drivers stations taking some wicked hits.

Re: Top speed?
 

There are long Velcro strips provided at the player stations this year - guess the GDC saw this coming!!

Re: Top speed?
 

But AFAIK, they are right in the middle of the stations therefore i see some teams having control mounting conflicts.

Re: Top speed?
 

the Velcro is clearly described in the rulebook, so teams should incorporate this into the design of their operator interface for this year.

Re: Top speed?
 

Agreed, and it's a good thing the GDC thought of this. Even the 7-10lb trackball could possibly knock down an unsecured interface, and this will be a guaranteed equipment saver during the hybrid period (Read as: 120LB robot plows into the alliance station at 12 ft/sec with no one holding the controls.)

Re: Top speed?
 

The laws of physics actually impose much lower speed limits than c, or even Mach 1.

Consider that the robot has to navigate a corner at each end of the track. A high traction wheel will have a co-efficient of friction of about 1.3. This limits the speed in the corner... or at least the speed that can be maintained through the corner without skidding into the walls.

It also limits the accelleration of the robot down the straights, and requires the driver to slow the robot before entering a corner (assuming that straight speed exceeds the maximum cornering speed.)

Some fairly simple kinematics calculations should allow teams to calculate the theoretical top speed and fastest lap time possible for a robot.

By the way, I note Squirell's reference to NASCAR... but isn't this more like NASACAR?


Jason

Re: Top speed?
 

They had them last year too. I'm encouraging my team to put Velcro on the bottom of their board.

Re: Top speed?
 

i think to fast could do damage to your own robot if not others lol try taking the 90 degree turns really fast and tell me you dont hit the wall

Re: Top speed?
 

A low center of gravity would help, although you COULD spin out as a result...maybe 20 ft/sec drive train is a little too fast?

Re: Top speed?
 

I think this year there will be robots exceeding 20 fps but these robots will also probably has sophisticated turning systems or eliminate the need to turn entirely (20 fps mecanum/holonomic/swerve). I think teams that used swerves last year may have an advantage the image of team 71 swerving around the rack at high speed sticks in my mind lol.

Re: Top speed?
 

Does anyone know if there's any rule about an unsafe speed or is that just a judge related matter?

Re: Top speed?
 

While I agree that you will see many robots going faster than 20fps, I doubt very many teams will do well that go that fast. The reason I say that is because winning races has more to do with control than speed, especially on a short track such as FIRST has provided.

No. I believe that this year the winners will be the robots with the best control over their drive system and the robots that can take the big hits from those that cannot control their drive systems.

Re: Top speed?
 

Seems like a decent way to take the turns...:p

Re: Top speed?
 

I scrolled through the manual, but I didn't see a specific rule.
Generally, the refs judge "unsafe speed" based on whether or not you have control over your machine. If you're going flying into walls, if you keep heading toward the outside of the field, if you're ramming into other robots, be prepared to be deemed unsafe.

But as long as you seem to VISIBLY have a handle on your machine and what it's doing, then you should be fine.

Re: Top speed?
 

It sure is.......

Go straight, turn left, turn left. Repeat endlessly!!!!!!!!! :D :D :D

Re: Top speed?
 

Alright, I'm doing the computations for the fastest theoretical lap.

I'm saying the straight is 27ft = 8.22m long.

A friction-limited single lap of overdrive includes:
A) a half-circle of radius r and length pi*r
B) a straight with [(8.22- 2r)/2]m of acceleration followed by (8.22 - 2r)/2]m of deceleration for a total of (8.22-2r) distance
A) another half-circle of radius r and length pi*r
B) another straight


Total distance: 2*pi*r + 2(8.22-2r) = 2*pi*r + 16.44 - 4r

Time tc for the circles will be determined by the centripetal equations.
t_c = pi*r / v_c
F_c = Ff = uFn = umg = -9.8mu
-9.8mu = -mv_cv_c/r
9.8u = v_cv_c/r
9.8ur = v_cv_c
v_c = sqrt(9.8ur)
t_c = pi*r / sqrt(9.8ur)

Time ts for the straights will be determined by straight-line acceleration and deceleration, which means we need the kinematic equations. Starting and ending speed for an ideal lap will be vc (our exit speed from the corners). Our acceleration will be friction-limited. Our distance is half the straight, which is (8.22-2r)/2 or 4.11-r
F = ma
Ff = ufn = 9.8mu
9.8mu = ma
9.8u = a // this is our acceleration due to friction


d = v_c*t + 0.5*a*t_s*t_s
4.11-r = sqrt(9.8ur)*0 + 0.5*(9.8u)*t_s*t_s
4.11-r = 4.8*u*t_s*t_s
sqrt( [4.11-r]/[4.8u] ) = t_s

So now that we know our time for the half-circles (t_c) and straights (2t_s), we can add it all together. There are 2 half-circles, 2 acceleration phases and 2 deceleration phases in a single friction-limited lap.
t_total = 2t_c + 4t_s
t_total = 2*pi*r / sqrt(9.8ur) + 4*sqrt( [4.11-r]/[4.8u] )

If you like calculus, sub in a known friction coefficient for u and then solve for the optimum turning radius. Since I have long since forgotten how to do a complicated derivative like I'd need to do here, I'm just going to sub in r = 13ft = 3.96m and u = 1.3.

t_total = 4.12 sec (laps per minute: 14)
Cornering speed = vc = sqrt(9.8ur) = 7.1m/s = 23fps

Edit: After graphing the result for u=1.3, I see that a 3.96m radius turn is very close to the WORST you can do for a friction-limited lap. You could be doing 2 second laps if you had a 50cm turn radius. However, the power output required to accelerate a 50kg robot at 1.3gs and slow it back down twice per lap is ludicrously high. Specifically, if you accelerated a 50kg robot at 1.3g for the 4.11m and decelerated just as fast for 4.11m, then you're looking at this much work:
W = F*d
W = 1.3*9.8*50*8.22 = 5236J of energy expended

Since we know our time for the 8.22m straights is 2*t_s = 2*sqrt( [4.11]/[4.8u] ) = 1.62s for the whole straight. This means your power output will be 3.2kW, which at 12 volts means you're drawing 268amps on the straights, assuming a perfectly efficient drivetrain and no resistance.

Re: Top speed?
 

this is where is all goes awry, since that does not exist :yikes: :yikes: :yikes:

Re: Top speed?
 

Along with the need to draw more amps than our breakers provide, the ability to accelerate hard enough that your tires rather than your motors are the limiting factor, the ability to turn controllably without losing velocity, the assumption that nobody would get in your way while you lapped, etc. It was all just a thinking exercise to figure out the absolute fastest laptime possible. The next step would be to constrain it so that your power output is less than 120amps and see what happens then.

Re: Top speed?
 

It's all relative... ;)

It all depends on what type of drive system you are going to be using I guess.

Re: Top speed?
 

There is no rule that specifically states that you must obey the law of physics during the competition. This may be an oversight.

Re: Top speed?
 

I believe that is covered by <General Rule 0>: the part about "...recognition of science..."

Re: Top speed?
 

last year we had a 16fps robot and if anyone was at the Milwaukee regional they would have seen our programming error where we went full forward for 2 secs and for got to put the stop in. Needles to say it was devistating we hit the far wall at full speed and thewheels just kept moving. Head ref estoped us and that was the end of that. It truly was a sight to see.

Re: Top speed?
 

This makes me chuckle a little bit. Last year, we had a 7fps crab system. Driving full forward and doing a 90 degree crab maneuver put a ton of stress on the drive modules. We cracked the hubs on quite a few wheels due to the tremendous side load. I can only imagine what would happen if the wheels of a robot moving 20fps were suddenly turned perpendicular to the direction of travel. :eek:

Re: Top speed?
 

I think you should consider that just like last year - in the absence of other robots you might be able to hang 10 or 11 tubes. When other robots are present, however, you are sometimes lucky to hang 3 or 4.

I would bet with slow movers on the course and having to dodge other robots, even disregarding hurdling and pushing balls, you'll average 8-10 second lap times.

Re: Top speed?
 

As I remeber hearing once. I don't care about the car that goes 0-55 inn 2.5 seconds. I want the car that can go from 80 - 50 in 1.2 seconds. It's not gonna just be how fast you get around the straightaway but can you survive the hairpin turn.

Re: Top speed?
 

I've been thinking. With a speed of 10fps it would take you about 5 seconds to travel the length of the field. Double that and add about 5 seconds overall turning time and you get a lap average of 15 seconds. This is of course without anything in your way.

If you did average 15 seconds a lap, the max number of laps you could do in two minutes is 8. Now if you started at the right spot, you can cross the finish line 9 times, scoring 18 points. This is even with traffic.

I'm not really expecting more than 5-7 laps for one robot in a match. No matter how fast you are going.

Re: Top speed?
 

Going around this turn reminds me a lot of autonomous mode of 2003, some teams would steer (mine included) and some teams had tank but would have wheel lowered on an angle that would steer them around the corner then bring it up into the chasis (312 did this and a few others but I can't remember them now)

Re: Top speed?
 

This is somewhat related to the topspeed discussion so I figure I'll ask it here. When determining the "top speed" of a robot in relation to it's gearing, wheels, motors, ect. what point on the motor curve are you taking the RPM numbers from? My team is a second year team with little or no help from any Mech E's and we are looking to do a bit more in terms of drivetrain design than we did last year.

So when someone says they have a 15fps or 16fps robot what RPM is that on the motor (assuming 2.5" CIM)?

Re: Top speed?
 

It depends on the size of your wheel. If you go 16 fps with 8 inch wheels then your motors will be rotating twice as fast at 16 fps with 4 inch wheels

Re: Top speed?
 

I can easily see teams doing laps under 10 seconds with a great line of travel, and no interference.

Whether or not this will happen is to be seen.

But it can, which to me is pretty darn awesome.

Re: Top speed?
 

It also depends on the team reporting that speed. Relatively few teams measure actual speed (I think the Martians do, but beyond that I can't think of anybody). So, then you get into theoretical calculations. Some teams approximate inefficiencies (JVN's famous .81% of free speed is an example), some just use the 12V free speed, and some report numbers based off of operation at 40A draw.

I wouldn't use the 40A one, because most of the time you aren't going to draw that much just driving around, and if you are you're probably in trouble. (40A per motor doesn't leave much wiggle room at all on either the motor breakers or the main breaker) Similarly, I highly doubt teams will be driving with their motors running at 12V free speed; however, there is something to be said for the argument that the battery doesn't output 12V, more like 13.5ish, and that can make up for some of the inefficiency losses. The approximation method may end up more accurate than either of the above, but that is obviously dependent on how accurate the inefficiency approximation itself is.

Personally, I just use free speed in calculations because it is easier to work with. In my experience, underestimating speed has worse consequences than overestimating (to many interrupts per sec, dead-reckoning autonomous driving too far, etc). Whatever you choose stick with one; you can then compare speeds year to year much easier than if you had to convert from one method to the other.

Re: Top speed?
 

...and that is exactly why I am referring to each lap around the track as an "orbit"

-dave

Re: Top speed?
 

I thought the 2008 game theme (driving around the track) was to honor Indianapolis, home of the Indy 500, NASCAR 400 and the 2010 FIRST Championship.... ;)

Re: Top speed?
 

We all know the only way to achieve the fastest possible lap time is to wear an white racing suit, and keep your identity secret.

Re: Top speed?
 

Haha I remember that. :yikes: I think we were up next so was able to get a good view of it. And someone on our team brought up that incident on Saturday. Anyways...

with 6 robots on the field, If there are a few that are hurdlers and some who just try to race around the track, I expect to see a lot of congestion. Hopefully the hurdlers have a low enough center of gravity that if they are hit at high speed, they wont hit the overpass and tip over.

Re: Top speed?
 

Does that mean the Lane Divider has a hidden gravitational force pulling on us that we can use to our advantage as we try and slingshot around it?? ;)

Re: Top speed?
 

Think of the possibilities for raw speed (forgetting the track balls for a moment). Stagger! Differential tire pressures! Jacking! Suspension systems! For the first time, a team with a World of Outlaws car builder will have an advantage!

Do robots push, or do they get loose? Last year, I didn't miss FRC, but this year is going to be painful. What a cool game.

(Actually, since I might be a scorekeeper this year, I think the game really stinks. Video scoring anyone?)

Re: Top speed?
 

Drifting robots... NOW THAT WOULD BE EXCITING! :cool:

Re: Top speed?
 

i know this is pretty unrelated to this topic but, when coming up for new tshirt designs for this year, we decided to go with a rather known quote from a new comedy racing movie that has been out for a little while. We get to the kickoff, see the game, and WOOWWWWW!! haha.

Re: Top speed?
 

That would be awesome. But how are you gonna find a Stig for every team!

Re: Top speed?
 

I think i remember that.... i seem to remember a bot driving across the field, heading straight at one of our alliance members bots...hit one of the supports on the side and spun into the wall right before it got there i think so it didnt hit the bot luckily lol

On another note...

now im not so good at the whole weight distribution thing but if you hand your center of gravity more to the left side of the bot wouldnt that help the bot turn sharper or quicker? I guess if there was too much weight to one side your bot wouldnt go very straight... but i dunno so yea

Re: Top speed?
 

haha i think after this competition is all said and done with we shall bring our robots out into the giant parking lots of these stadiums and have some good ole robot drag racing anyone with me?:D

Re: Top speed?
 

Is anyone besides me seeing robodonuts?

Re: Top speed?
 

My comment with regards to top speed is that there is no standard for what people are reporting their speeds as.

Some people are reporting theoretical speeds calculated from gear ratios and motor speeds. Which motor speed? Free speed is certainly not correct, nor is calculating it at 40A

My team empirically measured our 2007 bots speed to be 6.6fps (by timing it over a distance), and we were among the faster (by no means fastest) robots at GTR, and the 2 offseason events we went to.

We've modified our gear ratios to be faster this year. But all these people claiming 16-20fps will either be EXTREMELY uncontrollable, or have some radical drive system that allows control at such speeds. I mean, 20fps will have you from one end of the field to the other in about 2s, and you dont have to go ALL the way to the end of the field. Turning would be extremely sensitive with the typical tank style drive at this speed.

Re: Top speed?
 

I dont belive there is a top speed but just to be safe i would advise not going over 40.

Re: Top speed?
 

Heaven :D


The rules say we can push against the cage structure, does that mean we can use it like a motocross berm and square off the corners or do we just have take our chances in the loose stuff on the outside :)