Go Back   VEX Forum > Community > General Forum

General Forum Open Discussion of the VEX Robotics System that can be answered by anyone. VEX Robotics Engineers will not answer questions posted here; see Official VEX Technical Support below.

Reply
 
Thread Tools
  #11  
Old 05-10-2012, 11:18 PM
Previlant Previlant is offline
Junior Member
VEX # AURA
 
Join Date: Apr 2011
Location: Auckland, New Zealand
Posts: 10
Send a message via Skype™ to Previlant
Re: Shifting X-Drive

Also if anyone's interested, if you make the x drive past 45 degrees you would get more speed in one direction and more torque in the other direction, essentially making it like a shifting drive train without actually having shifting mechanisms.
http://www.youtube.com/watch?v=QLMWJQC71LA&feature=plcp
__________________
VRCC World Championships - 2nd after Qualification, and Judges Award

Last edited by Previlant; 05-10-2012 at 11:57 PM.
Reply With Quote
  #12  
Old 05-11-2012, 12:54 AM
dontworryaboutit's Avatar
dontworryaboutit dontworryaboutit is offline
Senior Member
VEX # 254D
 
Join Date: Mar 2010
Posts: 641
Images: 1
Re: Shifting X-Drive

Indeed a cool way to make an effective CVT (continuously variable transmission). But, I'm a little wary of that design because of the pivot point. Can it support the full weight of the robot?

Other than that though, very nice use of the speed advantage of an X-holonomic drive.
__________________
254D = 254Doesn't work at competition
254D = redefining "18 inches" since 2009
First make it work, then make it work well.
Reply With Quote
  #13  
Old 05-11-2012, 01:07 AM
bobsalive bobsalive is offline
Senior Member
VEX # AURA
 
Join Date: Mar 2009
Location: Auckland, NZ
Posts: 321
Images: 4
Re: Shifting X-Drive

Quote:
Originally Posted by dontworryaboutit View Post
Indeed a cool way to make an effective CVT (continuously variable transmission). But, I'm a little wary of that design because of the pivot point. Can it support the full weight of the robot?
We've got most of an arm/lift on that base right now, and it seems okay, although we haven't made it pick up a gazillion stacks yet. With our testing so far it seems that it should work, although that might change.

On a slightly unrelated side note, 254 borrowed two 60T gears from us at Worlds and we never got them back. (it's okay!)
__________________
Andrew - andrew.chen@aura.org.nz
Reply With Quote
  #14  
Old 05-11-2012, 02:35 AM
vdsa vdsa is offline
Senior Member
VEX # 2968
 
Join Date: Jun 2010
Location: Rangitikei, Lower North Island, NZ
Posts: 128
Re: Shifting X-Drive

Quote:
Originally Posted by dontworryaboutit View Post
Indeed a cool way to make an effective CVT (continuously variable transmission).
where's the continuous part?
Reply With Quote
  #15  
Old 05-11-2012, 03:04 AM
Vex Mundi's Avatar
Vex Mundi Vex Mundi is offline
Senior Member
VEX # AURA
 
Join Date: Mar 2011
Location: Auckland, New Zealand
Posts: 534
Images: 1
Send a message via Skype™ to Vex Mundi
Re: Shifting X-Drive

Quote:
Originally Posted by vdsa View Post
where's the continuous part?
If you use a continuous actuator instead of the pneumatic cylinder then you can get the full range of ratios 1 - ∞, not just 1 and 1.4.

We were hoping to be the first team on the forums to point that out, in our writeup of the offset X-drive Previn linked to, but I guess the cat is out of the bag now .
__________________
-Oliver | oliver.wilson@aura.org.nz || Aura Home | Our Photos | Our Videos
Reply With Quote
  #16  
Old 05-11-2012, 05:39 AM
mr. giggums mr. giggums is offline
Member
VEX # 355C
 
Join Date: Apr 2011
Location: Batavia, Illinois
Posts: 50
How would you calculate speed and torque if the offset is x degrees apart? I tried to figure this out but I don't know enough about vectors.
Reply With Quote
  #17  
Old 05-11-2012, 06:26 AM
Vex Mundi's Avatar
Vex Mundi Vex Mundi is offline
Senior Member
VEX # AURA
 
Join Date: Mar 2011
Location: Auckland, New Zealand
Posts: 534
Images: 1
Send a message via Skype™ to Vex Mundi
Re: Shifting X-Drive

Quote:
Originally Posted by mr. giggums View Post
How would you calculate speed and torque if the offset is x degrees apart? I tried to figure this out but I don't know enough about vectors.
I have a draft document on this that I'll try to upload tonight. I'll see if I can get our webmaster (bobsalive) to add it as a page on our website tomorrow.
__________________
-Oliver | oliver.wilson@aura.org.nz || Aura Home | Our Photos | Our Videos
Reply With Quote
  #18  
Old 05-11-2012, 09:30 AM
dontworryaboutit's Avatar
dontworryaboutit dontworryaboutit is offline
Senior Member
VEX # 254D
 
Join Date: Mar 2010
Posts: 641
Images: 1
Re: Shifting X-Drive

If the offset is X degrees from the wheel being pointed straight ahead, the force component straight ahead is given by cos(X) times the force when X = 0. The maximum speed is given by 1/cos(X) = sec(X) times the maximum speed when X = 0. You can verify this result by multiplying the speed by the force:
cos(X) * 1/cos(X) = 1
which says that you are not losing any energy as you rotate the wheels. You are losing a lot of energy to friction as X --> 90 degrees because the rollers are turning very fast.
__________________
254D = 254Doesn't work at competition
254D = redefining "18 inches" since 2009
First make it work, then make it work well.
Reply With Quote
  #19  
Old 05-11-2012, 11:59 AM
Vex Mundi's Avatar
Vex Mundi Vex Mundi is offline
Senior Member
VEX # AURA
 
Join Date: Mar 2011
Location: Auckland, New Zealand
Posts: 534
Images: 1
Send a message via Skype™ to Vex Mundi
Re: Shifting X-Drive

Yes, dontworryaboutit is right (as usual). Here is an in depth explanation if you are interested: https://docs.google.com/open?id=0B_I...0Q2aDBXeXlKb1U
__________________
-Oliver | oliver.wilson@aura.org.nz || Aura Home | Our Photos | Our Videos
Reply With Quote
  #20  
Old 05-11-2012, 12:11 PM
JoeG JoeG is offline
Senior Member
VEX # none
 
Join Date: Aug 2008
Location: Worcester, MA
Posts: 132
Images: 1
Send a message via AIM to JoeG
Re: Shifting X-Drive

The math checks out. An N-motor, Y-ratio "X" drive will move faster than an N-motor, Y-ratio tank drive. However, this is a little bit misleading. For a single speed system, you loose signifigant amounts of torque in the "X" drive. Therefore, the N-motor tank drive can be safely geared faster than the N-motor "X" drive, cancelling out the difference if we're talking about two separate robots.

Cool shifting concept though! Reminds me of this. I wonder if a similar linkage system could be applied to reduce the number of cylinders/air consumption required.
__________________
http://wordsaboutrobots.blogspot.com/, the place where I make words about making robots. UPDATED 7/30
FVC 53, 2005 pilot season.
VRC 2620A, 2008-2010, 2014-???
FRC 1687, 2007-2010, 2012-2014
FRC Rookie TBA, 2015-???

WPI 2015. Diversifying VEX linkages since 2008
Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

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

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


All times are GMT -6. The time now is 06:37 AM.


VEX and VEX Robotics are trademarks or service marks of Innovation First International, Inc.
Copyright © 2002-2013. All Rights Reserved. VEX Robotics, Inc. is a subsidiary of Innovation First International, Inc.
All other product names/marks of others are the property of their respective owners.