Go to Post I have never gone to a FIRST Robotics competition and not had fun. - mathking [more]
Home
Go Back   Chief Delphi > Competition > Rules/Strategy
CD-Media   CD-Spy  
portal register members calendar search Today's Posts Mark Forums Read FAQ rules

 
 
 
Thread Tools Rate Thread Display Modes
Prev Previous Post   Next Post Next
  #19   Spotlight this post!  
Unread 20-01-2009, 02:49
eugenebrooks eugenebrooks is offline
Team Role: Engineer
AKA: Dr. Brooks
no team (WRRF)
 
Join Date: Jan 2004
Rookie Year: 2001
Location: Livermore, CA
Posts: 601
eugenebrooks has a reputation beyond reputeeugenebrooks has a reputation beyond reputeeugenebrooks has a reputation beyond reputeeugenebrooks has a reputation beyond reputeeugenebrooks has a reputation beyond reputeeugenebrooks has a reputation beyond reputeeugenebrooks has a reputation beyond reputeeugenebrooks has a reputation beyond reputeeugenebrooks has a reputation beyond reputeeugenebrooks has a reputation beyond reputeeugenebrooks has a reputation beyond repute
Re: <R08> Section M

Use the measured figures for the coefficient of friction and you will be closer to reality with your estimates. Several teams have posted measured figures on CD, and their measurements are roughly twice the inline published values.

I would also like to say that a driver who accelerates all the way down the field and then crashes into the back wall, or into another robot near the back wall, is not engaging in an accident. A reasonable expectation is that drivers will be required to attempt to maintain control of their robots, and will be expected to plan their acceleration and braking so that they arrive at their destination without a high speed crash. I would at least hope that this will be the case, although I have not yet run across this expectation spelled out as I read the rules. I will have to read the rules a little more closely, I guess...

Eugene


Quote:
Originally Posted by dtengineering View Post
Okay... seeing as how my other car is still on this planet, I'm a bit hesitant to question these numbers, but I was doing some calculations with our programmers this evening to figure out peak velocities and such and have to question the assumed closure velocity cited here.

We used the published value of static coefficient (.06) of friction to determine that a 150 lb (68kg) robot would have a normal force of 668n and a peak forward force of 40N. The mass of the robot, plus trailer, is 186lb, or 84kg, giving a peak accelleration of 0.47 m/s/s

Next we assumed that the effective length of the playing field was 15m. Although 54 feet works out to be 16.5m, or thereabouts, the length of the robot and trailer, as well as the driver station bumpers must be subtracted from the space available for picking up speed.

Assuming constant acelleration, of .47m/s/s over 15m, it should take a minimum of 8 seconds to cross the playing field from one end to the other, with a peak impact velocity of 3.76 m/s or... 12.3 feet per second.

Now this is the peak velocity of a robot hitting the end... but it is also the maximum impact velocity that any two robots could sustain. If each started out at one end of the playing field, they would meet in the middle, and would each only have reached 6.15 fps each, for a closing velocity of 12.3 fps, which is just 2/3 of the assumed 18 fps velocity impact. (Actually it would be lower than 12.3fps, as the effective length of the playing field would again be diminished by the length of the second robot/trailer combo unit.)

That isn't to say that some robots might not exceed the published coefficient of friction as the playing field wears, or that a 12 fps impact is something to be laughed off without concern... we'll be building a solid robot and strapping solid bumpers on it... but the peak closure speed and resulting extreme G-forces didn't mesh with our calculations and we were wondering if we had somehow missed something.

Or, perhaps, if the 18fps impact velocity is based on actual testing of robots on regolith, then the published coefficients of friction don't provide an accurate estimation of robot performance. I know a few teams have posted suggesting that their experimental results for coefficients of friction are much higher than the published values.

Any suggestions?

Jason

<Edit> first assumption... that is not quite right. We assumed all of the weight of the trailer would be over the trailer wheels. Some of it will contribute to the normal force of the robot and thus improve traction and accelleration. Even assuming 100% of the trailer weight does so, however, peak accelleration is just .6 m/s/s and it takes 7 seconds to make the trip with a peak velocity of 14 fps. We're getting closer...

second assumption... we were assuming a straight line path from one end to the other... it may be possible to achieve a slightly higher peak velocity by taking a curved path along the playing surface... </edit>
 


Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
R08 Clarification Andy L Rules/Strategy 10 06-01-2009 18:42
complie error can not fit the section. Section xxxx Doug Leppard Programming 5 12-02-2008 09:44
Error - section 'UTIL_LIB' can not fit the section. Section 'UTIL_LIB' length=0x00000 BookerT Programming 13 27-01-2005 09:49
Error - section 'UTIL_LIB' can not fit the section. Section 'UTIL_LIB' length=0x00000 BookerT Programming 0 25-01-2005 19:17
Linking Errors: "section '????' can not fit the section. ..." Astronouth7303 Programming 3 16-01-2005 21:36


All times are GMT -5. The time now is 23:37.

The Chief Delphi Forums are sponsored by Innovation First International, Inc.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
Copyright © Chief Delphi