OCCRA
Go to Post And, just for the record, dlavery is on my mental ignore list from September until January if the thread involves the word "hint" at all. - Andrew Schreiber [more]
Home
Go Back   Chief Delphi > Technical > Technical Discussion
CD-Events   CD-Media   CD-Spy   FRC-Spy  
portal register members calendar search Today's Posts Mark Forums Read FAQ rules

 
Closed Thread
Thread Tools Rate Thread Display Modes
  #1   Spotlight this post!  
Unread 01-22-2002, 12:35 PM
Simon G Simon G is offline
Registered User
no team (Cheshire Choppers)
 
Join Date: Jan 2002
Location: Cheshire, CT
Posts: 10
Simon G is an unknown quantity at this point
Smile Traction Limited, rather than torque

I've been reading all these posts on motors and gears (and been struggling myself with gearbox design) when a thought struck me - it is quite possible that our robots may be traction limited, rather than torque limited:

That is, assume we had an infinite torque drivetrain. What would be the limitation on the robot if it was chained to a wall? At some point, whatever we were using for wheels / treads etc. would break traction and slip. Therefore, that traction limit would define the maximum torque through the system and propelling our robots, yes?

So I offer that we should be mindful that given all the power of our new chippy motors, we might easily reach the limits of traction, unless we design the whole system (including traction devices), rather than just the drive system. What's the point of designing a drive system that can handle 315 oz-in or more of input torque, when our wheels or treads slip at 150 oz-in?

Am I thinking this through correctly, or am I missing something??

My $0.02.
Simon
  #2   Spotlight this post!  
Unread 01-22-2002, 12:49 PM
P.J. Baker's Avatar
P.J. Baker P.J. Baker is offline
needs a clever user title
FRC #0177 (Bobcat Robotics)
Team Role: Engineer
 
Join Date: May 2001
Rookie Year: 1999
Location: Hebron, CT
Posts: 110
P.J. Baker is a glorious beacon of lightP.J. Baker is a glorious beacon of lightP.J. Baker is a glorious beacon of lightP.J. Baker is a glorious beacon of lightP.J. Baker is a glorious beacon of light
Traction Limited is the way to go.

You really don't want unlimited traction, because it will lead to stalled motors & or damaged carpet. Neither of these are good things.

If you don't worry about traction in your design, you will not be likely to realize the benefit of all that torque, but if your traction is too good, you'll find yourself tripping breakers and shredding carpet.

Just something to keep in mind.

P.J.
  #3   Spotlight this post!  
Unread 01-22-2002, 09:11 PM
GregT GregT is offline
Registered User
no team
 
Join Date: Jul 2001
Rookie Year: 2001
Location: FL
Posts: 400
GregT will become famous soon enough
Send a message via AIM to GregT
Hmmm... really makes ya think, eh?



Greg
__________________
The above was my opinion. I'm wrong a lot. I'm sarcastic a lot. Try not to take me too seriously.
  #4   Spotlight this post!  
Unread 01-22-2002, 09:54 PM
Jon Lawton Jon Lawton is offline
Bitter FIRST Cynic
no team
 
Join Date: Oct 2001
Location: San Jose, California
Posts: 209
Jon Lawton is an unknown quantity at this point
Send a message via ICQ to Jon Lawton Send a message via AIM to Jon Lawton
I AGREE! Our team had enough trobule transmitting the torque of two drill motors in low gear (2:1 to wheels, large sprocket on wheel) to the ground! I hate to see what it will be like this year...

BUT of course we have three 181lb objects we could pick up to increase our normal force. Now how can we do that? Hmmm...
  #5   Spotlight this post!  
Unread 01-22-2002, 11:33 PM
Anton Abaya's Avatar
Anton Abaya Anton Abaya is offline
Registered User
None #0419 (Rambots)
 
Join Date: Jun 2001
Rookie Year: 1999
Location: Boston
Posts: 215
Anton Abaya has a spectacular aura aboutAnton Abaya has a spectacular aura aboutAnton Abaya has a spectacular aura about
Send a message via ICQ to Anton Abaya Send a message via AIM to Anton Abaya
how do you calculate the traction of your wheels/treads/drive train traction into in-lbs?

i'm curious to figure ours out.
  #6   Spotlight this post!  
Unread 01-23-2002, 02:56 AM
Jon Lawton Jon Lawton is offline
Bitter FIRST Cynic
no team
 
Join Date: Oct 2001
Location: San Jose, California
Posts: 209
Jon Lawton is an unknown quantity at this point
Send a message via ICQ to Jon Lawton Send a message via AIM to Jon Lawton
Quote:
Originally posted by Anton Abaya
how do you calculate the traction of your wheels/treads/drive train traction into in-lbs?

i'm curious to figure ours out.
Okay... well... I'm no engeneer (not even close) but this is how I wound up understanding:

Get a fish scale. Hook it to your robot parallel to the plane the center of your wheels are on. Increase power to motors until you loose traction. You can use the dashboard port to see the PWM value you were at, and I think you could then extrapolate the torque/rpm of the motor at the time. Why the scale? The force you should read should be equal to your coefficent of friction times your normal force (weight). F=uM.

Since we know a goal takes 32-35lb of force to move, you can use this little test to see if you really can move four!

Like I said, I'm not the mechanics man, so can a more authoritative source back me up on this?
  #7   Spotlight this post!  
Unread 01-23-2002, 06:08 AM
Lloyd Burns Lloyd Burns is offline
Registered User
FRC #1246 (Agincourt Robotics)
Team Role: Engineer
 
Join Date: Jun 2001
Rookie Year: 1997
Location: Toronto
Posts: 292
Lloyd Burns is an unknown quantity at this point
Quote:
Originally posted by Anton Abaya
how do you calculate the traction of your wheels/treads/drive train traction into in-lbs?

i'm curious to figure ours out.
Using the friction-pull test above, you know the force; Force (in lbs from a spring scale) times radius of the drive wheels (in inches) will produce the torque at the wheel hub. All the rest is gear / sprocket tooth ratio.
Closed Thread


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
traction questions AlbertW Rules/Strategy 2 01-05-2003 04:58 PM
Power, speed, and torque... AGH Gui Cavalcanti Technical Discussion 5 11-10-2002 06:02 PM
Friction, traction, torque - oh my... Gui Cavalcanti Technical Discussion 30 08-13-2002 05:01 PM
How fast could a torque motor turn if a torque motor could.. archiver 2001 0 06-23-2002 09:54 PM
Gear Woes Simon G Technical Discussion 14 01-24-2002 03:31 PM


All times are GMT -5. The time now is 11:17 AM.

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


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Copyright © Chief Delphi