Go to Post It doesn't matter if you write a thousand lines of code for a robot, if you didn't teach and/or inspire the HS students as you did it then you are not a mentor. - JamesBrown [more]
Home
Go Back   Chief Delphi > Technical > Technical Discussion
CD-Media   CD-Spy  
portal register members calendar search Today's Posts Mark Forums Read FAQ rules

 
Closed Thread
Thread Tools Rate Thread Display Modes
  #16   Spotlight this post!  
Unread 02-08-2010, 23:04
RyanN's Avatar
RyanN RyanN is offline
RyanN
AKA: Ryan Nazaretian
FRC #4901 (Garnet Squadron)
Team Role: Mentor
 
Join Date: Jun 2006
Rookie Year: 2005
Location: Columbia, SC
Posts: 1,126
RyanN has a reputation beyond reputeRyanN has a reputation beyond reputeRyanN has a reputation beyond reputeRyanN has a reputation beyond reputeRyanN has a reputation beyond reputeRyanN has a reputation beyond reputeRyanN has a reputation beyond reputeRyanN has a reputation beyond reputeRyanN has a reputation beyond reputeRyanN has a reputation beyond reputeRyanN has a reputation beyond repute
Re: Drop-center drivetrains: Why?

Quote:
Originally Posted by Al Skierkiewicz View Post
Simply put, without dropping the center wheels, drive motors rapidly go to stall current in turns.
And when drive motors rapidly go to stall current, that means...
  1. Robot doesn't turn
  2. Breakers pop
  3. or Worse

We've been using 6WD with dropped center wheels for years (with the exception of last year).

We like using pneumatic center wheels. Makes adjusting the offset very easy.
__________________
Garnet Squadron
FRC 4901
Controls Mentor
@rnazaretian

Previous mentor and student from Team Fusion, FRC 364
  #17   Spotlight this post!  
Unread 02-08-2010, 23:36
Ian Curtis Ian Curtis is offline
Best Available Data
FRC #1778 (Chill Out!)
Team Role: Engineer
 
Join Date: Feb 2005
Rookie Year: 2004
Location: Puget Sound
Posts: 2,521
Ian Curtis has a reputation beyond reputeIan Curtis has a reputation beyond reputeIan Curtis has a reputation beyond reputeIan Curtis has a reputation beyond reputeIan Curtis has a reputation beyond reputeIan Curtis has a reputation beyond reputeIan Curtis has a reputation beyond reputeIan Curtis has a reputation beyond reputeIan Curtis has a reputation beyond reputeIan Curtis has a reputation beyond reputeIan Curtis has a reputation beyond repute
Re: Drop-center drivetrains: Why?

Quote:
Originally Posted by EricH View Post
It's simpler, unless the game requires pointing in one direction for any length of time (like 2 seconds to unload a game object). The defensive robots love 6WD robots that have omnis on the corners, something about they're easier to knock out of position rotationally.
1276 built a launcher in 2008 with a 6 wheel drive with omnis in the corners. I was sure we would get knocked all over the place trying to launch, but it was never an issue. We would've done it again in 2009 were it not for the slippery floor, and the team disbanding in 2010.

That said, in 2008 there wasn't a lot of incentive to knock robots silly, so we may have just gotten lucky.

As a counterpoint to my own counterpoint, I can't think of many situations where if someone is trying to rotate you, you'd be much better off with the stickier wheels. In 2010 if someone was messing with you, you'd drive off before kicking the ball. In 2007, you were probably entangled in the Rack, so the squirrelyness (technical term) might help you swing around to another Spider. In 2006 if someone was pushing on you, it was probably enough to throw off your aim. Additionally, it cut way down on our distance (though our conveyor to our shooter and shooter wheels were all on one CIM, so this may have been less of an issue for others). In 2005, perhaps it could help you stick your ground for just an extra second, but this came turned out so offensively, I'd rather not be rocking back and forth with a 10 pound tetra 10 feet up in the air.
__________________
CHILL OUT! | Aero Stability & Control Engineer
Adam Savage's Obsessions (TED Talk) (Part 2)
It is much easier to call someone else a genius than admit to yourself that you are lazy. - Dave Gingery
  #18   Spotlight this post!  
Unread 03-08-2010, 00:53
billbo911's Avatar
billbo911 billbo911 is offline
I prefer you give a perfect effort.
AKA: That's "Mr. Bill"
FRC #2073 (EagleForce)
Team Role: Mentor
 
Join Date: Mar 2005
Rookie Year: 2005
Location: Elk Grove, Ca.
Posts: 2,367
billbo911 has a reputation beyond reputebillbo911 has a reputation beyond reputebillbo911 has a reputation beyond reputebillbo911 has a reputation beyond reputebillbo911 has a reputation beyond reputebillbo911 has a reputation beyond reputebillbo911 has a reputation beyond reputebillbo911 has a reputation beyond reputebillbo911 has a reputation beyond reputebillbo911 has a reputation beyond reputebillbo911 has a reputation beyond repute
Re: Drop-center drivetrains: Why?

Quote:
Originally Posted by JamesCH95 View Post
For all of the analysis that could go into a chassis like that it is simpler to use omni wheels on the corners and be done with it. That frees up all the time and energy saved in chassis analysis for use in more unique challenges.
Let's look at this a bit more. It's not always as simple as you have stated here. There are situations, or game elements, that do not lend themselves very well to a robot with omni's on the four corners.
If you are playing on a flat surface, then you bet, omni's on the corners is a simple solution. Now, if you want to climb a ramp, or go over a bump, then omni's on the corners add a whole new level of difficulty. I'm not talking so much about traction, but the need to hit the incline squarely. If you are out of alignment by only a few degrees then the robot will tend to slide out, or fall back to the level surface. The steeper the incline, the greater this effect will be.

The bottom line is, make the design decisions based on what you want to achieve in the specific game you will be playing with the robot.
__________________
CalGames 2009 Autonomous Champion Award winner
Sacramento 2010 Creativity in Design winner, Sacramento 2010 Quarter finalist
2011 Sacramento Finalist, 2011 Madtown Engineering Inspiration Award.
2012 Sacramento Semi-Finals, 2012 Sacramento Innovation in Control Award, 2012 SVR Judges Award.
2012 CalGames Autonomous Challenge Award winner ($$$).
2014 2X Rockwell Automation: Innovation in Control Award (CVR and SAC). Curie Division Gracious Professionalism Award.
2014 Capital City Classic Winner AND Runner Up. Madtown Throwdown: Runner up.
2015 Innovation in Control Award, Sacramento.
2016 Chezy Champs Finalist, 2016 MTTD Finalist
  #19   Spotlight this post!  
Unread 03-08-2010, 00:54
Chris is me's Avatar
Chris is me Chris is me is offline
no bag, vex only, final destination
AKA: Pinecone
FRC #0228 (GUS Robotics); FRC #2170 (Titanium Tomahawks)
Team Role: Mentor
 
Join Date: Dec 2008
Rookie Year: 2006
Location: Glastonbury, CT
Posts: 7,718
Chris is me has a reputation beyond reputeChris is me has a reputation beyond reputeChris is me has a reputation beyond reputeChris is me has a reputation beyond reputeChris is me has a reputation beyond reputeChris is me has a reputation beyond reputeChris is me has a reputation beyond reputeChris is me has a reputation beyond reputeChris is me has a reputation beyond reputeChris is me has a reputation beyond reputeChris is me has a reputation beyond repute
Send a message via AIM to Chris is me
Re: Drop-center drivetrains: Why?

Quote:
Originally Posted by AdamHeard View Post
We're not engineers, small correction. Statement is true otherwise.
aspiring to be engineers

Quote:
Originally Posted by JamesCH95 View Post
For all of the analysis that could go into a chassis like that it is simpler to use omni wheels on the corners and be done with it. That frees up all the time and energy saved in chassis analysis for use in more unique challenges.
I really think "just use omnis" can be a pretty poor solution depending on the game challenge. If you have a long arm, a gentle tap moves your game piece several feet away and there's not much resistance to speak of. Really, it's not that hard to do "all of the analysis". I can tell you what the analysis will say right now: The more rigid your chassis, the better your 6WD can perform. Building a rigid chassis doesn't take tons of time and energy. Even if you do want to do careful and thorough analysis for such a drivetrain, it's not exactly a huge resource drain, and depending on the challenge it could result in a much, much better chassis for your needs.

While some games you probably could get away with a chassis with four omnis, in the past I think more often than not you couldn't. Being spun off target in Aim High, knocking you away from your spider leg in Rack 'n Roll, or taking a mid to long range shot in Breakaway are all situations when I'd rather have a bit more resistance to being spun.
__________________
Mentor / Drive Coach: 228 (2016-?)
...2016 Waterbury SFs (with 3314, 3719), RIDE #2 Seed / Winners (with 1058, 6153), Carver QFs (with 503, 359, 4607)
Mentor / Consultant Person: 2170 (2017-?)
---
College Mentor: 2791 (2010-2015)
...2015 TVR Motorola Quality, FLR GM Industrial Design
...2014 FLR Motorola Quality / SFs (with 341, 4930)
...2013 BAE Motorola Quality, WPI Regional #1 Seed / Delphi Excellence in Engineering / Finalists (with 20, 3182)
...2012 BAE Imagery / Finalists (with 1519, 885), CT Xerox Creativity / SFs (with 2168, 118)
Student: 1714 (2009) - 2009 Minnesota 10,000 Lakes Regional Winners (with 2826, 2470)
2791 Build Season Photo Gallery - Look here for mechanism photos My Robotics Blog (Updated April 11 2014)

Last edited by Chris is me : 03-08-2010 at 01:02.
  #20   Spotlight this post!  
Unread 03-08-2010, 08:35
Brandon Holley's Avatar
Brandon Holley Brandon Holley is offline
Chase perfection. Catch excellence.
AKA: Let's bring CD back to the way it used to be
FRC #0125 (NU-TRONs, Team #11 Alumni (GO MORT))
Team Role: Engineer
 
Join Date: Jan 2004
Rookie Year: 2001
Location: Boston, MA
Posts: 2,593
Brandon Holley has a reputation beyond reputeBrandon Holley has a reputation beyond reputeBrandon Holley has a reputation beyond reputeBrandon Holley has a reputation beyond reputeBrandon Holley has a reputation beyond reputeBrandon Holley has a reputation beyond reputeBrandon Holley has a reputation beyond reputeBrandon Holley has a reputation beyond reputeBrandon Holley has a reputation beyond reputeBrandon Holley has a reputation beyond reputeBrandon Holley has a reputation beyond repute
Send a message via AIM to Brandon Holley
Re: Drop-center drivetrains: Why?

Quote:
Originally Posted by iCurtis View Post
As a counterpoint to my own counterpoint, I can't think of many situations where if someone is trying to rotate you, you'd be much better off with the stickier wheels. In 2010 if someone was messing with you, you'd drive off before kicking the ball. In 2007, you were probably entangled in the Rack, so the squirrelyness (technical term) might help you swing around to another Spider. In 2006 if someone was pushing on you, it was probably enough to throw off your aim. Additionally, it cut way down on our distance (though our conveyor to our shooter and shooter wheels were all on one CIM, so this may have been less of an issue for others). In 2005, perhaps it could help you stick your ground for just an extra second, but this came turned out so offensively, I'd rather not be rocking back and forth with a 10 pound tetra 10 feet up in the air.
I don't know about your reasoning here. It seems in every instance you brought up that someone trying to rotate you is prohibiting you from completing your initial task. In your 2010 example instead of kicking the ball you drive away because someones "messing with you". In 2007 you are swinging from the initial spider your trying to cap to a different one because your being rotated. In 2006 being lined up and not moving was key for 90% of the shooters out there, obviously. In 2005 getting to where you needed to get to was absolutely key.

Not meaning to nitpick here, but the suggestions you make are all alternative maneuvers your team can make to offset being spun easily. In all those instances, I would much rather not be spun and complete the task my team wants to, than come up with a new game plan because someone is playing D on me.

-Brando
__________________
MORT (Team 11) '01-'05 :
-2005 New Jersey Regional Chairman's Award Winners
-2013 MORT Hall of Fame Inductee

NUTRONs (Team 125) '05-???
2007 Boston Regional Winners
2008 & 2009 Boston Regional Driving Tomorrow's Technology Award
2010 Boston Regional Creativity Award
2011 Bayou Regional Finalists, Innovation in Control Award, Boston Regional Finalists, Industrial Design Award
2012 New York City Regional Winners, Boston Regional Finalists, IRI Mentor of the Year
2013 Orlando Regional Finalists, Industrial Design Award, Boston Regional Winners, Pine Tree Regional Finalists
2014 Rhode Island District Winners, Excellence in Engineering Award, Northeastern University District Winners, Industrial Design Award, Pine Tree District Chairman's Award, Pine Tree District Winners
2015 South Florida Regional Chairman's Award, NU District Winners, NEDCMP Industrial Design Award, Hopper Division Finalists, Hopper/Newton Gracious Professionalism Award
  #21   Spotlight this post!  
Unread 03-08-2010, 08:42
IKE's Avatar
IKE IKE is offline
Not so Custom User Title
AKA: Isaac Rife
no team (N/A)
Team Role: Mechanical
 
Join Date: Jan 2008
Rookie Year: 2003
Location: Michigan
Posts: 2,149
IKE has a reputation beyond reputeIKE has a reputation beyond reputeIKE has a reputation beyond reputeIKE has a reputation beyond reputeIKE has a reputation beyond reputeIKE has a reputation beyond reputeIKE has a reputation beyond reputeIKE has a reputation beyond reputeIKE has a reputation beyond reputeIKE has a reputation beyond reputeIKE has a reputation beyond repute
Re: Drop-center drivetrains: Why?

Make sure when discussing "performance" to use key words like traction, ability to hold ground, ease of turning, manuverability...
Saying "XYZ will perform better" in a thread like this can lead to misconceptions. Many of the parameters for manuverabilty and the ability to hold ones ground are in direct conflict.
  #22   Spotlight this post!  
Unread 03-08-2010, 08:49
JamesCH95's Avatar
JamesCH95 JamesCH95 is offline
Hardcore Dork
AKA: JCH
FRC #0095 (The Grasshoppers)
Team Role: Engineer
 
Join Date: Dec 2004
Rookie Year: 2001
Location: Enfield, NH
Posts: 1,849
JamesCH95 has a reputation beyond reputeJamesCH95 has a reputation beyond reputeJamesCH95 has a reputation beyond reputeJamesCH95 has a reputation beyond reputeJamesCH95 has a reputation beyond reputeJamesCH95 has a reputation beyond reputeJamesCH95 has a reputation beyond reputeJamesCH95 has a reputation beyond reputeJamesCH95 has a reputation beyond reputeJamesCH95 has a reputation beyond reputeJamesCH95 has a reputation beyond repute
Re: Drop-center drivetrains: Why?

Quote:
Originally Posted by billbo911 View Post
Now, if you want to climb a ramp, or go over a bump, then omni's on the corners add a whole new level of difficulty. I'm not talking so much about traction, but the need to hit the incline squarely. If you are out of alignment by only a few degrees then the robot will tend to slide out, or fall back to the level surface. The steeper the incline, the greater this effect will be.
Although we did not use omni wheels this year, we did us mecanums, and we noticed that the robot wouldn't glance off inclines, but rather tend to align with them. There probably is some angle where the robot would tend to glance off rather than self-align, but my experience tells me that this angle is sufficiently wide to easily drive over a bump or up a ramp.

Quote:
Originally Posted by Chris is me View Post
I really think "just use omnis" can be a pretty poor solution depending on the game challenge. If you have a long arm, a gentle tap moves your game piece several feet away and there's not much resistance to speak of. Really, it's not that hard to do "all of the analysis". I can tell you what the analysis will say right now: The more rigid your chassis, the better your 6WD can perform. Building a rigid chassis doesn't take tons of time and energy. Even if you do want to do careful and thorough analysis for such a drivetrain, it's not exactly a huge resource drain, and depending on the challenge it could result in a much, much better chassis for your needs.

While some games you probably could get away with a chassis with four omnis, in the past I think more often than not you couldn't. Being spun off target in Aim High, knocking you away from your spider leg in Rack 'n Roll, or taking a mid to long range shot in Breakaway are all situations when I'd rather have a bit more resistance to being spun.
Perhaps you did not understand that I was referring to a 6wd chassis with two traction wheels in the center and four omni wheels on the corners. In my experience these have been fairly resistant to being spun and do not rock much, if at all; a good compromise in my opinion.

I was not referring to a chassis stiffness analysis, but rather keeping track of CG location for the purposes of reducing rocking while manipulating a game piece. While these are both straight-forward analyses to perform, not every team has a lab full of CAD-capable computers and/or trained operators ready to do them.
__________________
Theory is a nice place, I'd like to go there one day, I hear everything works there.

Maturity is knowing you were an idiot, common sense is trying to not be an idiot, wisdom is knowing that you will still be an idiot.
  #23   Spotlight this post!  
Unread 03-08-2010, 14:47
Chris is me's Avatar
Chris is me Chris is me is offline
no bag, vex only, final destination
AKA: Pinecone
FRC #0228 (GUS Robotics); FRC #2170 (Titanium Tomahawks)
Team Role: Mentor
 
Join Date: Dec 2008
Rookie Year: 2006
Location: Glastonbury, CT
Posts: 7,718
Chris is me has a reputation beyond reputeChris is me has a reputation beyond reputeChris is me has a reputation beyond reputeChris is me has a reputation beyond reputeChris is me has a reputation beyond reputeChris is me has a reputation beyond reputeChris is me has a reputation beyond reputeChris is me has a reputation beyond reputeChris is me has a reputation beyond reputeChris is me has a reputation beyond reputeChris is me has a reputation beyond repute
Send a message via AIM to Chris is me
Re: Drop-center drivetrains: Why?

Quote:
Originally Posted by JamesCH95 View Post
Perhaps you did not understand that I was referring to a 6wd chassis with two traction wheels in the center and four omni wheels on the corners. In my experience these have been fairly resistant to being spun and do not rock much, if at all; a good compromise in my opinion.

I was not referring to a chassis stiffness analysis, but rather keeping track of CG location for the purposes of reducing rocking while manipulating a game piece. While these are both straight-forward analyses to perform, not every team has a lab full of CAD-capable computers and/or trained operators ready to do them.
I caught that. 6 wheel 4 omni isn't terrible or anything but it is more easily spun and negates a lot of the advantages of a rocking drivetrain. The CG issue, while relevant, really isn't something you need computer precision to analyze. If you don't want to rock with an arm too much, you can adjust the drop a little, put the CG a bit more to one side fore-aft, or even run an 8 wheel drive if your CG is centered. You should be able to get a good enough estimate with just some napkin sketches of where the "heavy stuff" goes. CAD isn't required to figure it out.

Even if you do find you need more precision than "I think it'd be best if we put the battery... here", CG analysis is always beneficial on a competition robot.
__________________
Mentor / Drive Coach: 228 (2016-?)
...2016 Waterbury SFs (with 3314, 3719), RIDE #2 Seed / Winners (with 1058, 6153), Carver QFs (with 503, 359, 4607)
Mentor / Consultant Person: 2170 (2017-?)
---
College Mentor: 2791 (2010-2015)
...2015 TVR Motorola Quality, FLR GM Industrial Design
...2014 FLR Motorola Quality / SFs (with 341, 4930)
...2013 BAE Motorola Quality, WPI Regional #1 Seed / Delphi Excellence in Engineering / Finalists (with 20, 3182)
...2012 BAE Imagery / Finalists (with 1519, 885), CT Xerox Creativity / SFs (with 2168, 118)
Student: 1714 (2009) - 2009 Minnesota 10,000 Lakes Regional Winners (with 2826, 2470)
2791 Build Season Photo Gallery - Look here for mechanism photos My Robotics Blog (Updated April 11 2014)

Last edited by Chris is me : 03-08-2010 at 14:49.
  #24   Spotlight this post!  
Unread 03-08-2010, 14:54
Cory's Avatar
Cory Cory is offline
Registered User
AKA: Cory McBride
FRC #0254 (The Cheesy Poofs)
Team Role: Engineer
 
Join Date: May 2002
Rookie Year: 2001
Location: Redwood City, CA
Posts: 6,812
Cory has a reputation beyond reputeCory has a reputation beyond reputeCory has a reputation beyond reputeCory has a reputation beyond reputeCory has a reputation beyond reputeCory has a reputation beyond reputeCory has a reputation beyond reputeCory has a reputation beyond reputeCory has a reputation beyond reputeCory has a reputation beyond reputeCory has a reputation beyond repute
Send a message via AIM to Cory
Re: Drop-center drivetrains: Why?

People refer to "rocking" all the time and cite it as a problem with manipulators.

Think about the math here. With a 33" wheelbase (37" long chassis, with 4" wheels), that means you have 16.5" between wheels. With a .1875" drop on the center, you can rock 1/100 of a degree. Obviously that's exaggerated when you have a long arm sticking out, but come on. .010 degrees of rock is nothing. It's hardly noticeable. It doesn't affect precise positioning whatsoever.
__________________
2001-2004: Team 100
2006-Present: Team 254
  #25   Spotlight this post!  
Unread 03-08-2010, 14:58
JesseK's Avatar
JesseK JesseK is offline
Expert Flybot Crasher
FRC #1885 (ILITE)
Team Role: Mentor
 
Join Date: Mar 2007
Rookie Year: 2005
Location: Reston, VA
Posts: 3,695
JesseK has a reputation beyond reputeJesseK has a reputation beyond reputeJesseK has a reputation beyond reputeJesseK has a reputation beyond reputeJesseK has a reputation beyond reputeJesseK has a reputation beyond reputeJesseK has a reputation beyond reputeJesseK has a reputation beyond reputeJesseK has a reputation beyond reputeJesseK has a reputation beyond reputeJesseK has a reputation beyond repute
Re: Drop-center drivetrains: Why?

An interesting idea inspired by this thread would be to (gasp!) raise the center wheel on the fly in order to reduce turnability similar to the nonadrive concept.

Hmm.
__________________

Drive Coach, 1885 (2007-present)
CAD Library Updated 5/1/16 - 2016 Curie/Carver Industrial Design Winner
GitHub
  #26   Spotlight this post!  
Unread 03-08-2010, 14:59
AdamHeard's Avatar
AdamHeard AdamHeard is offline
Lead Mentor
FRC #0973 (Greybots)
Team Role: Mentor
 
Join Date: Oct 2004
Rookie Year: 2004
Location: Atascadero
Posts: 5,508
AdamHeard has a reputation beyond reputeAdamHeard has a reputation beyond reputeAdamHeard has a reputation beyond reputeAdamHeard has a reputation beyond reputeAdamHeard has a reputation beyond reputeAdamHeard has a reputation beyond reputeAdamHeard has a reputation beyond reputeAdamHeard has a reputation beyond reputeAdamHeard has a reputation beyond reputeAdamHeard has a reputation beyond reputeAdamHeard has a reputation beyond repute
Send a message via AIM to AdamHeard
Re: Drop-center drivetrains: Why?

Quote:
Originally Posted by Cory View Post
People refer to "rocking" all the time and cite it as a problem with manipulators.

Think about the math here. With a 33" wheelbase (37" long chassis, with 4" wheels), that means you have 16.5" between wheels. With a .1875" drop on the center, you can rock 1/100 of a degree. Obviously that's exaggerated when you have a long arm sticking out, but come on. .010 degrees of rock is nothing. It's hardly noticeable. It doesn't affect precise positioning whatsoever.
Agreed.

Even with a 10' arm on there, if your manipulator needs to be accurate in placement to 2" or less, you really have a poorly designed manipulator that would be difficult to score with anyway.
  #27   Spotlight this post!  
Unread 03-08-2010, 15:00
AdamHeard's Avatar
AdamHeard AdamHeard is offline
Lead Mentor
FRC #0973 (Greybots)
Team Role: Mentor
 
Join Date: Oct 2004
Rookie Year: 2004
Location: Atascadero
Posts: 5,508
AdamHeard has a reputation beyond reputeAdamHeard has a reputation beyond reputeAdamHeard has a reputation beyond reputeAdamHeard has a reputation beyond reputeAdamHeard has a reputation beyond reputeAdamHeard has a reputation beyond reputeAdamHeard has a reputation beyond reputeAdamHeard has a reputation beyond reputeAdamHeard has a reputation beyond reputeAdamHeard has a reputation beyond reputeAdamHeard has a reputation beyond repute
Send a message via AIM to AdamHeard
Re: Drop-center drivetrains: Why?

Quote:
Originally Posted by JesseK View Post
An interesting idea inspired by this thread would be to (gasp!) raise the center wheel on the fly in order to reduce turnability similar to the nonadrive concept.

Hmm.
For what "benefit"?

Before people start going off and design new for the sake of new, they should evaluate what a well designed full treaded drop center 6wd can do. There is a reason 60 started doing it, 254/968 always does, and we always love to copy it.
  #28   Spotlight this post!  
Unread 03-08-2010, 15:04
JamesCH95's Avatar
JamesCH95 JamesCH95 is offline
Hardcore Dork
AKA: JCH
FRC #0095 (The Grasshoppers)
Team Role: Engineer
 
Join Date: Dec 2004
Rookie Year: 2001
Location: Enfield, NH
Posts: 1,849
JamesCH95 has a reputation beyond reputeJamesCH95 has a reputation beyond reputeJamesCH95 has a reputation beyond reputeJamesCH95 has a reputation beyond reputeJamesCH95 has a reputation beyond reputeJamesCH95 has a reputation beyond reputeJamesCH95 has a reputation beyond reputeJamesCH95 has a reputation beyond reputeJamesCH95 has a reputation beyond reputeJamesCH95 has a reputation beyond reputeJamesCH95 has a reputation beyond repute
Re: Drop-center drivetrains: Why?

Quote:
Originally Posted by Chris is me View Post
I caught that. 6 wheel 4 omni isn't terrible or anything but it is more easily spun and negates a lot of the advantages of a rocking drivetrain. The CG issue, while relevant, really isn't something you need computer precision to analyze. If you don't want to rock with an arm too much, you can adjust the drop a little, put the CG a bit more to one side fore-aft, or even run an 8 wheel drive if your CG is centered. You should be able to get a good enough estimate with just some napkin sketches of where the "heavy stuff" goes. CAD isn't required to figure it out.
I am aware that CG/tipping moments can be roughly estimated with napkin calculations. Chassis stiffness is not analyzed so easily.

We've also done a drive-train with two omni wheels in the middle and traction wheels on four corners these omni+traction 6wd robots, in either configuration, have all been successful.

I'm not trying to invalidate your points, Chris, they are indeed accurate. While the does trade off a little hit-and-spin stability, it also gains turning speed and virtually eliminates jitters from scrubbing the outside wheels and rocking. As with any robot design choice it has to be made in context of the teams strategy in that year's game. I feel that this disclaimer need not be made with every post though.
__________________
Theory is a nice place, I'd like to go there one day, I hear everything works there.

Maturity is knowing you were an idiot, common sense is trying to not be an idiot, wisdom is knowing that you will still be an idiot.
  #29   Spotlight this post!  
Unread 03-08-2010, 18:24
Ian Curtis Ian Curtis is offline
Best Available Data
FRC #1778 (Chill Out!)
Team Role: Engineer
 
Join Date: Feb 2005
Rookie Year: 2004
Location: Puget Sound
Posts: 2,521
Ian Curtis has a reputation beyond reputeIan Curtis has a reputation beyond reputeIan Curtis has a reputation beyond reputeIan Curtis has a reputation beyond reputeIan Curtis has a reputation beyond reputeIan Curtis has a reputation beyond reputeIan Curtis has a reputation beyond reputeIan Curtis has a reputation beyond reputeIan Curtis has a reputation beyond reputeIan Curtis has a reputation beyond reputeIan Curtis has a reputation beyond repute
Re: Drop-center drivetrains: Why?

Perhaps you were blessed with better drivers than us. It just seemed that the vast majority of the time we were being defended, it was a better use of our time to leave and sneak to a different location rather than wiggle back and forth with someone slamming on us.

Quote:
Originally Posted by Brandon Holley View Post
I don't know about your reasoning here. It seems in every instance you brought up that someone trying to rotate you is prohibiting you from completing your initial task. In your 2010 example instead of kicking the ball you drive away because someones "messing with you". In 2007 you are swinging from the initial spider your trying to cap to a different one because your being rotated. In 2006 being lined up and not moving was key for 90% of the shooters out there, obviously. In 2005 getting to where you needed to get to was absolutely key.

Not meaning to nitpick here, but the suggestions you make are all alternative maneuvers your team can make to offset being spun easily. In all those instances, I would much rather not be spun and complete the task my team wants to, than come up with a new game plan because someone is playing D on me.

-Brando
Cory, we had issues with rocking and the dropped center wheel, but we may have dropped more than .1875, it's been a while. In 2006 when shooting from the floor, rocked one way we would make shots, rocked the other way they went high (or low). We also had some tracking issues with our dead reckoning autonomous.
__________________
CHILL OUT! | Aero Stability & Control Engineer
Adam Savage's Obsessions (TED Talk) (Part 2)
It is much easier to call someone else a genius than admit to yourself that you are lazy. - Dave Gingery
  #30   Spotlight this post!  
Unread 04-08-2010, 08:11
Unsung FIRST Hero
Al Skierkiewicz Al Skierkiewicz is offline
Broadcast Eng/Chief Robot Inspector
AKA: Big Al WFFA 2005
FRC #0111 (WildStang)
Team Role: Engineer
 
Join Date: Jun 2001
Rookie Year: 1996
Location: Wheeling, IL
Posts: 10,792
Al Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond repute
Re: Drop-center drivetrains: Why?

We have (on more than one occasion) used a dropped a foot under the front or back of the robot to assist in turning. This raises one set of wheels off the ground.
For some of the other discussion, there is no substitute for practice.

A common joke among music professionals goes like this...
A person on a street in New York is asked "How do you get to Carnegie Hall?". The response is "practice, practice, practice!"
__________________
Good Luck All. Learn something new, everyday!
Al
WB9UVJ
www.wildstang.org
________________________
Storming the Tower since 1996.
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
pic: Center Player Station and Ball Drop Wetzel Extra Discussion 2 08-01-2006 17:40
Center to Center Distance for 2002 Chaiphua and Cluster gear sanddrag Motors 1 20-07-2005 07:36
Omnidirectional drivetrains patrickrd Technical Discussion 21 11-10-2002 10:54
Drivetrains archiver 2001 14 23-06-2002 22:52


All times are GMT -5. The time now is 01:47.

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