Go to Post Totally agree on the fact that legal strategies are... legal. - Kevin Sevcik [more]
Home
Go Back   Chief Delphi > ChiefDelphi.com Website > Extra Discussion
CD-Media   CD-Spy  
portal register members calendar search Today's Posts Mark Forums Read FAQ rules

 
Reply
Thread Tools Rating: Thread Rating: 2 votes, 5.00 average. Display Modes
  #16   Spotlight this post!  
Unread 13-11-2015, 21:39
RobotsThatWork's Avatar
RobotsThatWork RobotsThatWork is offline
Registered User
AKA: Adithya Bellathur
FRC #0649 (M-SET Fish)
 
Join Date: Sep 2015
Rookie Year: 2011
Location: Saratoga, CA
Posts: 16
RobotsThatWork is an unknown quantity at this point
Re: pic: Butterfly Drive

Quote:
Originally Posted by Tom Line View Post
I'm interested in the side-to-side module design. How do you insure it puts enough force down onto the floor so that the wheels don't slide?
You mean the strafing module, right?

We took inspiration from 148's strafing module (from their 2014 robot, Vader). The module itself spins on the axle that's powered by the CIM. So when the CIM is powered, the module spins down until a wheel contacts the wheel. The CIM will exert enough force to push down the module enough to have the ground exert a normal force on the wheel (which is what traction is dependent on) before the torque of the CIM spins the omniwheel.

At least that's how I understood it while designing this. We haven't actually done more serious math outside of a simple free body diagram. If someone from 148 or anyone with experience with this type of strafing module could explain more/clarify/prove me wrong, that would be awesome.
Reply With Quote
  #17   Spotlight this post!  
Unread 13-11-2015, 23:20
Tom Line's Avatar
Tom Line Tom Line is offline
Raptors can't turn doorknobs.
FRC #1718 (The Fighting Pi)
Team Role: Mentor
 
Join Date: Jan 2007
Rookie Year: 1999
Location: Armada, Michigan
Posts: 2,513
Tom Line has a reputation beyond reputeTom Line has a reputation beyond reputeTom Line has a reputation beyond reputeTom Line has a reputation beyond reputeTom Line has a reputation beyond reputeTom Line has a reputation beyond reputeTom Line has a reputation beyond reputeTom Line has a reputation beyond reputeTom Line has a reputation beyond reputeTom Line has a reputation beyond reputeTom Line has a reputation beyond repute
Re: pic: Butterfly Drive

Quote:
Originally Posted by RobotsThatWork View Post
You mean the strafing module, right?

We took inspiration from 148's strafing module (from their 2014 robot, Vader). The module itself spins on the axle that's powered by the CIM. So when the CIM is powered, the module spins down until a wheel contacts the wheel. The CIM will exert enough force to push down the module enough to have the ground exert a normal force on the wheel (which is what traction is dependent on) before the torque of the CIM spins the omniwheel.

At least that's how I understood it while designing this. We haven't actually done more serious math outside of a simple free body diagram. If someone from 148 or anyone with experience with this type of strafing module could explain more/clarify/prove me wrong, that would be awesome.
Yep. That's what I'm talking about. The diameter of the wheel, clearance from the ground when horizontal, and gearing all play a role in how much normal force the wheel can exert on the ground.

We struggled with tuning the amount of force our strafing modules needed in 2015, but that was going over the bump + with and without totes, so it had to move more weight / accelerate more mass than just a robot and that weight varied quite a bit.

I looked at 148's design when thinking about ours, but we had one shot at getting it right (we swapped our drive from mechanum to this at state champs) so I ended up going with 2 strafe modules, held down with gas shocks counter balanced by surgical tubing so we could adjust the downward force.

The 148 solution is lighter and more elegant, but more difficult to get right.
Reply With Quote
  #18   Spotlight this post!  
Unread 14-11-2015, 22:41
KohKohPuffs KohKohPuffs is online now
Registered User
AKA: Daniel Koh
FRC #0299 (Valkyrie Robotics)
Team Role: CAD
 
Join Date: Jun 2015
Rookie Year: 2013
Location: Saratoga, CA
Posts: 119
KohKohPuffs has a spectacular aura aboutKohKohPuffs has a spectacular aura aboutKohKohPuffs has a spectacular aura about
Re: pic: Butterfly Drive

Hm... so I think the main issue revolves around when the tractions are down and the robot gets hit on the side, which might damage the modules, and the shaft especially over time. In addition, the way the piston is mounted probably also causes it to receive a lot of force on impact.

I might consider another design of the Butterfly, although I might move on to intakes or something other than drivetrains, because I've been doing that a lot. But anyways, here's what I was thinking about the new design:
  • Module goes into a 3x2 boxtubing; there I can maybe make the modules almost as wide as the interior of the tube to have minimal flex and bending (this is my logic to this problem, but I might be wrong...)
  • Pistons push down on the modules without any special mounting, similar to Neutrino's design
  • Change in material of the module plates. Maybe something like polycarbonate? Not really sure on this one: I know polycarb is flexible, but to some extent
__________________
-KohKoh

115 MVRT, Driver (2013-2015)
649 M-SET, CAD (2015-2016)
299 Valkyrie Robotics, Mechanical Director (2016 - present)
Reply With Quote
  #19   Spotlight this post!  
Unread 14-11-2015, 23:05
Greg Woelki's Avatar
Greg Woelki Greg Woelki is offline
FRC Alumnus
FRC #1768
 
Join Date: May 2014
Rookie Year: 2013
Location: Bolton, MA
Posts: 97
Greg Woelki is a glorious beacon of lightGreg Woelki is a glorious beacon of lightGreg Woelki is a glorious beacon of lightGreg Woelki is a glorious beacon of lightGreg Woelki is a glorious beacon of light
Re: pic: Butterfly Drive

Quote:
Originally Posted by RobotsThatWork View Post
You mean the strafing module, right?

We took inspiration from 148's strafing module (from their 2014 robot, Vader). The module itself spins on the axle that's powered by the CIM. So when the CIM is powered, the module spins down until a wheel contacts the wheel. The CIM will exert enough force to push down the module enough to have the ground exert a normal force on the wheel (which is what traction is dependent on) before the torque of the CIM spins the omniwheel.

At least that's how I understood it while designing this. We haven't actually done more serious math outside of a simple free body diagram. If someone from 148 or anyone with experience with this type of strafing module could explain more/clarify/prove me wrong, that would be awesome.
My understanding of 148's strafing module design is that it works even better than that. The wheel in contact with the ground rotates in the opposite direction as the module itself tips, meaning that the wheel is basically driving itself into the ground. For an intuition of this, consider the boundary cases (module tilt angles close to 0 degrees and close to 90 degrees). While the omni wheel would just skip along the ground if it made contact while the module was barely tilted, at close to 90 degrees it would actually be able to lift the robot up, supporting most of its weight. Obviously one would want to design for a tilt angle somewhere between these extremes, but they illustrate what's going on very well. The great thing about this design is that the normal force on the strafing wheel varies drastically depending on what the robot is doing, so you only have high normal force on the strafing wheel when high torque is applied to it.

For those more knowledgeable than I: Is my understanding correct?

Edit: As far as I can tell, it would follow from this understanding that, in theory, a tilt angle from horizontal of greater than the inverse tangent of the wheel-to-ground coefficient of friction would guarantee that the wheel wouldn't slip (Well, until the point at which the linear relationship between torque and normal force ends because there simply isn't more weight available for the strafe wheel to support). However, in reality, friction is also a fickle beast and is highly dependent on the exact conditions of the interaction at any given time.

Last edited by Greg Woelki : 14-11-2015 at 23:41.
Reply With Quote
  #20   Spotlight this post!  
Unread 15-11-2015, 22:01
RobotsThatWork's Avatar
RobotsThatWork RobotsThatWork is offline
Registered User
AKA: Adithya Bellathur
FRC #0649 (M-SET Fish)
 
Join Date: Sep 2015
Rookie Year: 2011
Location: Saratoga, CA
Posts: 16
RobotsThatWork is an unknown quantity at this point
Re: pic: Butterfly Drive

Quote:
Originally Posted by Greg Woelki View Post
...
Yeah you're right. I remember discussing this with someone when we watched the reveal video for the first time in 2014. But I completely forgot this time around, even while reviewing this CAD...
Reply With Quote
  #21   Spotlight this post!  
Unread 16-11-2015, 11:27
efoote868 efoote868 is offline
foote stepped in
AKA: E. Foote
FRC #0868
Team Role: Mentor
 
Join Date: Mar 2006
Rookie Year: 2005
Location: Noblesville, IN
Posts: 1,381
efoote868 has a reputation beyond reputeefoote868 has a reputation beyond reputeefoote868 has a reputation beyond reputeefoote868 has a reputation beyond reputeefoote868 has a reputation beyond reputeefoote868 has a reputation beyond reputeefoote868 has a reputation beyond reputeefoote868 has a reputation beyond reputeefoote868 has a reputation beyond reputeefoote868 has a reputation beyond reputeefoote868 has a reputation beyond repute
Re: pic: Butterfly Drive

Have you considered putting springs on the modules to hold them in place without air pressure?

There's nothing quite like losing air pressure in the middle of the match and being unable to drive.
__________________
Be Healthy. Never Stop Learning. Say It Like It Is. Own It.

Like our values? Flexware Innovation is looking for Automation Engineers. Check us out!
Reply With Quote
Reply


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


All times are GMT -5. The time now is 17:56.

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