Re: how fast are you
 

Isn't the ratio useless without knowing the wheel diameter?

Re: how fast are you
 

The calculation does appear to be correct, just go to http://www.usfirst.org/robotics/2004/specsheets.htm and try the calculations yourself.

Re: how fast are you
 

Our top speed this year was about 8 ft/sec. However, we were a little underpowered with only the two bosch motors for drive.

Re: how fast are you
 

Actually, Blizzard 5 (that's our robot...) outputs 500.6 lb-ft (6007 lb-in) at the drive wheels in low, and 116.4 lb-ft (1397 lb-in) in high--though that's before factoring in the estimated 86% efficiency--so let's call it 5166 and 1201 lb-in, respectively. Given that it's using the Fisher-Price motors in addition to the Bosch and CIM motors used by mechman108's robot, and given that its torque was calculated using a similar method, it looks about right. (Also note that these are stall torque ratings--the robot would most definitely not like being stalled for very long. 670 A will do that to you.)
A car's torque rating is measured at the crankshaft--but with a multi-motor drivetrain in a robot, there's no equivalent. So we measure torque at the drive wheels. The true test of car vs. robot involves factoring in whatever gear ratios exist in the car's transmission and differential, and comparing those figures.
Incidentally, like Steve said, we do 3.8 ft/s in low, and 16.5 ft/s in high (with 8.5" diameter wheels).

Re: how fast are you
 

Both these torque ratings are impractical because they are torques at stall and when 2 CIMs and 2 Drills stall the current draw is over 450A with each drawing 100A so it would be a very short time before several fuses blow. Add two FPs and getting to stall torque is even less possible. It would be more appropriate to list the torque at realistic currents like 40A per motor. Torque is basically proportional current so that is about 1/3 the torque listed for each of those robots. Supposing they could be at stall for more than a very short time, something would surely give to lower the torque very quickly, be it wheels slipping or the finger of the poor kid who got to close to the chain.

The fact that these are ratings at stall is another reason that they are incomparable with cars because internal combustion engines usually have max torque at higher speeds (at their highest speed?).

[edit] interesting little calculation: 500.6lb/ft on 12 inch wheels yields a force of 1001.2 lb per side. This would require wheels with a coefficient of friction of (1001.2)*2/130 = 15.4 to harness that power. The highest CoF i have seen in any context is like 3 or 4[/edit]

Re: how fast are you
 

We have a mathematical cruising speed of 10.5 on our one speed at peak parabola howvere at NAts when we put in onthe dynometer we tipped their scales or something and wernt getting an accurate read (we havea torwque of 0? ) but the thing was saying like 11.5

Re: how fast are you
 

Well if you were checking your top free spinning speed, then hopefully the dynamo is free spinning. Hence 0 torque.

Re: how fast are you
 

Our robot (Team 900) had a theoretical top speed of a little less than 10 ft/sec but we started this high so that with efficiency loss we would be down to around 8. We had a little too much speed so during our regionals we swapped out our 40 tooth sprockets for some 45 tooth sprockets. This put us down to 6.7 ft/sec on the dyno at nationals. We used both the Bosch and the Chip with an output to a 10 tooth sprocket-----to a 45 tooth.
-Aaron

Re: how fast are you
 

Correct! And that's why we don't like stalling motors. The whole point of the exercise is not to stall the motors--if we were to do that, we'd be lucky if we had 5 seconds before the main breaker went off (if the chart Bussman provided is any indication). And it is perfectly legitimate that the coefficient of friction limits the amount of torque that can be effectively used--once again, if the full torque were used, the motors would stall.

Re: how fast are you
 

theoretically... my mile would be around 3:20... my 100m 11.65....
but... im sure not able to run a mile that fast....

well our robot was theoretically 8fps....
how accurate theoretically it is, i have no idea

Re: how fast are you
 

Our robot went about 7-8 fps in low gear and 18 fps in high. heh we had no need for it but it was fun to drive. :)

Re: how fast are you
 

H.O.M.E.R(that's the robots name) does 12 ft/sec in high and 4 ft/sec in low using 2 Drills and 2 Atwoods/CIM/Chips with 6" wheels.

Re: how fast are you
 

you are right. the wheel size is a factor, but I just wanted to see what the average speed and what people might have used for reductions. Maybe a better question would be what is the overall ratio.

Re: how fast are you
 

We have two speeds - 4 fps in low gear and 15 fps in high gear

Re: how fast are you
 

Our bot this year was designed at a little more than 14fps with an overall gear ratio of 20.25:1 using 2 CIM motors. Actual performance was about 12.89 fps which gave us an overall drivetrain efficiency of about 86%.