OCCRA
Go to Post What is the coefficient of friction between butt and carpet? - JVN [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

 
Reply
Thread Tools Rate Thread Display Modes
  #1   Spotlight this post!  
Unread 08-28-2017, 05:37 PM
nuclearnerd's Avatar
nuclearnerd nuclearnerd is offline
Speaking for myself, not my team
AKA: Brendan Simons
FRC #5406 (Celt-X)
Team Role: Engineer
 
Join Date: Jan 2014
Rookie Year: 2014
Location: Hamilton, Ontario, Canada
Posts: 569
nuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond repute
Your daily dose of ridiculousness - 775 pro differential swerve

I drew this up on the weekend to see if I could. I was inspired by the awesome swerve posted here: https://www.chiefdelphi.com/media/photos/45452? and I remembered the differential swerve idea posted here: https://www.chiefdelphi.com/forums/s...d.php?t=152705. My goal was to come up with a compact swerve module, run by two 775 pros, which handled both power and steering (via differential speed). Here's the (incomplete) result.

The advantage is that, even if you cap the 775 pros at 10V to avoid burnout, and you leave 100W in reserve for steering, the two motors could put down 450W onto the carpet, which is nearly 30% more than a single CIM. It's also saves like two pounds per module.

The disadvantages are many The gearbox needs some custom gears presently, although there's probably other arrangements that would work with COTS parts. Good control of the speed of each motor is critical, and a failure of either motor, or any encoder/pot (not shown) would not be graceful.

I probably won't build this, but I thought I'd throw it out there for inspiration and laughs.
Attached Thumbnails
Click image for larger version

Name:	cx18_diff-swerve_sketch1.PNG
Views:	1342
Size:	423.1 KB
ID:	22496  Click image for larger version

Name:	cx18_diff-swerve_sketch2.PNG
Views:	869
Size:	294.4 KB
ID:	22497  

Last edited by nuclearnerd : 08-28-2017 at 06:23 PM.
Reply With Quote
  #2   Spotlight this post!  
Unread 08-28-2017, 05:59 PM
Andrew_L's Avatar
Andrew_L Andrew_L is offline
GA w/ a voice made for silent films
AKA: Entitled volunteer - do not hire
FRC #1323 (Madtown Robotics) #299 (Valkyrie Robotics)
Team Role: Mentor
 
Join Date: Sep 2016
Rookie Year: 2011
Location: San Jose
Posts: 304
Andrew_L has a reputation beyond reputeAndrew_L has a reputation beyond reputeAndrew_L has a reputation beyond reputeAndrew_L has a reputation beyond reputeAndrew_L has a reputation beyond reputeAndrew_L has a reputation beyond reputeAndrew_L has a reputation beyond reputeAndrew_L has a reputation beyond reputeAndrew_L has a reputation beyond reputeAndrew_L has a reputation beyond reputeAndrew_L has a reputation beyond repute
Re: Your daily dose of ridiculousness - 775 pro differential swerve

This looks great, Brenden! Would you be open to sharing the CAD?
Reply With Quote
  #3   Spotlight this post!  
Unread 08-28-2017, 06:05 PM
nuclearnerd's Avatar
nuclearnerd nuclearnerd is offline
Speaking for myself, not my team
AKA: Brendan Simons
FRC #5406 (Celt-X)
Team Role: Engineer
 
Join Date: Jan 2014
Rookie Year: 2014
Location: Hamilton, Ontario, Canada
Posts: 569
nuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond repute
Re: Your daily dose of ridiculousness - 775 pro differential swerve

Quote:
Originally Posted by Andrew_L View Post
This looks great, Brenden! Would you be open to sharing the CAD?
Sure, it's here:
Solidworks: https://drive.google.com/open?id=0B1...GVPSnlzU0ZoNGs
STEP: https://drive.google.com/open?id=0B1...TJtampPSVdIWHc

Be warned I just slapped it together to show the concept, so there's lots of details missing (encoder mounts, shaft retainers, proper gear and bearing bores, spacers, clearances, etc). Feel free to take it and improve it, but please share any results - I'd love to see the real thing.
Reply With Quote
  #4   Spotlight this post!  
Unread 08-28-2017, 06:07 PM
Bryce2471's Avatar
Bryce2471 Bryce2471 is offline
Alumnus
AKA: Bryce Croucher
FRC #2471 (Team Mean Machine)
Team Role: Mechanical
 
Join Date: Feb 2013
Rookie Year: 2007
Location: Camas, WA
Posts: 517
Bryce2471 has a brilliant futureBryce2471 has a brilliant futureBryce2471 has a brilliant futureBryce2471 has a brilliant futureBryce2471 has a brilliant futureBryce2471 has a brilliant futureBryce2471 has a brilliant futureBryce2471 has a brilliant futureBryce2471 has a brilliant futureBryce2471 has a brilliant futureBryce2471 has a brilliant future
Re: Your daily dose of ridiculousness - 775 pro differential swerve

This is hilarious, awesome, and very clever. Great job.
Up till the very end of your post I was not expecting it to be coaxial. I can't say that I would like to build one of these, but I'd like to see someone try it. It seems like steering might be a real hassle, but I think this might spur some further ideas in people.
__________________
FLL Team Future imagineers
2010 Oregon State Championships: Winners
2011 International Invite: First place Robot design, Second Place Robot Performance
FRC Team Mean Machine
2012 Seattle: Winning alliance
2013 Portland: Winning alliance
2013 Spokane: Winning alliance
2014 Wilsonville: Winning alliance
2014 Worlds: Deans List Winner
Reply With Quote
  #5   Spotlight this post!  
Unread 08-28-2017, 06:10 PM
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: 5,764
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: Your daily dose of ridiculousness - 775 pro differential swerve

The real question is who is talented enough to control it?
__________________
973 shirts for sale!
2x1 and 2x2 1/16" wall tubing for sale!

Need help? Check out 973 Remote Assistance and Mentorship Program.
Like our Robots? Check out the CAD files of MOST of our robots!

2017 "World Champions"
2014 Galileo Champions
2011 World Champions
Reply With Quote
  #6   Spotlight this post!  
Unread 08-28-2017, 06:18 PM
sanddrag sanddrag is offline
On to my 17th year in FRC
FRC #0696 (Circuit Breakers)
Team Role: Teacher
 
Join Date: Jul 2002
Rookie Year: 2002
Location: Glendale, CA
Posts: 8,626
sanddrag has a reputation beyond reputesanddrag has a reputation beyond reputesanddrag has a reputation beyond reputesanddrag has a reputation beyond reputesanddrag has a reputation beyond reputesanddrag has a reputation beyond reputesanddrag has a reputation beyond reputesanddrag has a reputation beyond reputesanddrag has a reputation beyond reputesanddrag has a reputation beyond reputesanddrag has a reputation beyond repute
Re: Your daily dose of ridiculousness - 775 pro differential swerve

Quote:
Originally Posted by AdamHeard View Post
The real question is who is talented enough to control it?
Jared (and probably a few others). I'm sure Ether could work us through the math and physics on it.
__________________
Teacher/Engineer/Machinist - Team 696 Circuit Breakers, 2011 - Present
Mentor/Engineer/Machinist, Team 968 RAWC, 2007-2010
Technical Mentor, Team 696 Circuit Breakers, 2005-2007
Student Mechanical Leader and Driver, Team 696 Circuit Breakers, 2002-2004
Reply With Quote
  #7   Spotlight this post!  
Unread 08-28-2017, 06:20 PM
nuclearnerd's Avatar
nuclearnerd nuclearnerd is offline
Speaking for myself, not my team
AKA: Brendan Simons
FRC #5406 (Celt-X)
Team Role: Engineer
 
Join Date: Jan 2014
Rookie Year: 2014
Location: Hamilton, Ontario, Canada
Posts: 569
nuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond repute
Re: Your daily dose of ridiculousness - 775 pro differential swerve

Quote:
Originally Posted by AdamHeard View Post
The real question is who is talented enough to control it?
I nominate 971.
Reply With Quote
  #8   Spotlight this post!  
Unread 08-28-2017, 06:40 PM
Andrew_L's Avatar
Andrew_L Andrew_L is offline
GA w/ a voice made for silent films
AKA: Entitled volunteer - do not hire
FRC #1323 (Madtown Robotics) #299 (Valkyrie Robotics)
Team Role: Mentor
 
Join Date: Sep 2016
Rookie Year: 2011
Location: San Jose
Posts: 304
Andrew_L has a reputation beyond reputeAndrew_L has a reputation beyond reputeAndrew_L has a reputation beyond reputeAndrew_L has a reputation beyond reputeAndrew_L has a reputation beyond reputeAndrew_L has a reputation beyond reputeAndrew_L has a reputation beyond reputeAndrew_L has a reputation beyond reputeAndrew_L has a reputation beyond reputeAndrew_L has a reputation beyond reputeAndrew_L has a reputation beyond repute
Re: Your daily dose of ridiculousness - 775 pro differential swerve

Quote:
Originally Posted by nuclearnerd View Post
I nominate 971.
The day 971 does a differential swerve is the day I admit to being Farmer John.
Reply With Quote
  #9   Spotlight this post!  
Unread 08-28-2017, 06:50 PM
Jjmase123's Avatar
Jjmase123 Jjmase123 is offline
Registered User
AKA: JJ Mase
FRC #1661 (Griffitrons)
Team Role: Driver
 
Join Date: Oct 2016
Rookie Year: 2014
Location: Los Angeles
Posts: 15
Jjmase123 is a jewel in the roughJjmase123 is a jewel in the roughJjmase123 is a jewel in the roughJjmase123 is a jewel in the rough
Re: Your daily dose of ridiculousness - 775 pro differential swerve

I too was experimenting with a differential swerve design. I'm curious to see how well the differential at the wheel itself would work, given slippage and other factors.

In the design I'm currently working on, the differential is above the slew bearing and the bottom carriage is similar to an "older" swerve design. The two bevel gears 180 degrees from another (there's 4 bevel gears meshed together) in the differential would be bolted to the inside of the bearing and thus rotate the module. Surely what I'm envisioning isn't as compact as your design (props to you for that amazingly compact coaxial design), but I'm curious to see the difference of placing the differential at the wheel itself or higher upstream in the geartrain. Please share if you've got any insight on this.

I know my explanation is quite questionable, so here's a picture to help envision it. This isn't the exact design, but somewhat close.



Lastly, where do you plan on placing the encoders? You're gonna need 8 of them to control motor RPM, nevermind 4 more if you want real-world angle values from the module's rotation (unless I'm wrong here).
__________________
Reply With Quote
  #10   Spotlight this post!  
Unread 08-28-2017, 06:50 PM
nuclearnerd's Avatar
nuclearnerd nuclearnerd is offline
Speaking for myself, not my team
AKA: Brendan Simons
FRC #5406 (Celt-X)
Team Role: Engineer
 
Join Date: Jan 2014
Rookie Year: 2014
Location: Hamilton, Ontario, Canada
Posts: 569
nuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond repute
Re: Your daily dose of ridiculousness - 775 pro differential swerve

Quote:
Originally Posted by Bryce2471 View Post
This is hilarious, awesome, and very clever. It seems like steering might be a real hassle, but I think this might spur some further ideas in people.
Yeah I'm pretty sure the steering would be pretty twitchy. The steering gear ratio comes out to maybe 40:1 (I think. Should be about twice the drive ratio) on a 775 pro. Compare that to this thread, where 100:1 on a (slower) bag motor is recommended for steering.

[Edit] I just recalculated that the steering ratio would be more like 2/3 the drive ratio (ie faster than drive) in this model, so definitely twitchy. That probably needs a redo.

Last edited by nuclearnerd : 08-29-2017 at 01:24 AM.
Reply With Quote
  #11   Spotlight this post!  
Unread 08-28-2017, 07:05 PM
Unsung FIRST Hero
Karthik Karthik is offline
Registered User
no team
Team Role: Mentor
 
Join Date: Apr 2002
Rookie Year: 1998
Location: Toronto, Ontario, Canada
Posts: 2,435
Karthik has a reputation beyond reputeKarthik has a reputation beyond reputeKarthik has a reputation beyond reputeKarthik has a reputation beyond reputeKarthik has a reputation beyond reputeKarthik has a reputation beyond reputeKarthik has a reputation beyond reputeKarthik has a reputation beyond reputeKarthik has a reputation beyond reputeKarthik has a reputation beyond reputeKarthik has a reputation beyond repute
Re: Your daily dose of ridiculousness - 775 pro differential swerve

Quote:
Originally Posted by AdamHeard View Post
The real question is who is talented enough to control it?
1114 prototyped differential swerve modules back in the summer of 2006. We never got too far with it, because that design was created when you were only allowed 4 CIMs, and dedicating 2 CIMs to a module seemed ridiculous (albeit not too ridiculous for a summer project). That being said the development of controls algorithms was difficult to say the least. However, with the new motor rules and the general advancements of software abilities of FRC teams, I would not be surprised to see someone try and field a differential swerve drive this season.
__________________
:: Karthik Kanagasabapathy ::
"Enthusiasm is one of the most powerful engines of success. When you do a thing, do it with all your might. Put your whole soul into it. Stamp it with your own personality. Be active, be energetic, be enthusiastic and faithful and you will accomplish your object. Nothing great was ever achieved without enthusiasm" -- R.W. Emerson
My TEDx Talk - The Subtle Secrets of Success
Reply With Quote
  #12   Spotlight this post!  
Unread 08-28-2017, 08:13 PM
Skyehawk's Avatar
Skyehawk Skyehawk is online now
Nuts N' Bolts
AKA: Skye Leake
FRC #0876 (Thunder Robotics)
Team Role: Mentor
 
Join Date: Nov 2012
Rookie Year: 2011
Location: Northwood, ND
Posts: 447
Skyehawk has a brilliant futureSkyehawk has a brilliant futureSkyehawk has a brilliant futureSkyehawk has a brilliant futureSkyehawk has a brilliant futureSkyehawk has a brilliant futureSkyehawk has a brilliant futureSkyehawk has a brilliant futureSkyehawk has a brilliant futureSkyehawk has a brilliant futureSkyehawk has a brilliant future
Re: Your daily dose of ridiculousness - 775 pro differential swerve

Quote:
Originally Posted by nuclearnerd View Post
I drew this up on the weekend to see if I could. I was inspired by the awesome swerve posted here: https://www.chiefdelphi.com/media/photos/45452? and I remembered the differential swerve idea posted here: https://www.chiefdelphi.com/forums/s...d.php?t=152705. My goal was to come up with a compact swerve module, run by two 775 pros, which handled both power and steering (via differential speed). Here's the (incomplete) result.

The advantage is that, even if you cap the 775 pros at 10V to avoid burnout, and you leave 100W in reserve for steering, the two motors could put down 450W onto the carpet, which is nearly 30% more than a single CIM. It's also saves like two pounds per module.

The disadvantages are many The gearbox needs some custom gears presently, although there's probably other arrangements that would work with COTS parts. Good control of the speed of each motor is critical, and a failure of either motor, or any encoder/pot (not shown) would not be graceful.

I probably won't build this, but I thought I'd throw it out there for inspiration and laughs.
So where can I get wooden 775 pros
In all serious though, I love seeing designs like this from the community, and it looks oh so pretty...
__________________
My time in FIRST has made me a better person, frankly I don't know where I'd be without it.


2011 Lake Superior Regional Champs (Thanks 2512 & 3747)
2015 Central Illinois Regional Engineering Inspiration Award Recipients
2016 Central Illinois Regional Champs (Thanks 2481 & 2220)
2017 Northern Lights Regional Chairmans Award Recipients
Reply With Quote
  #13   Spotlight this post!  
Unread 08-28-2017, 09:15 PM
nuclearnerd's Avatar
nuclearnerd nuclearnerd is offline
Speaking for myself, not my team
AKA: Brendan Simons
FRC #5406 (Celt-X)
Team Role: Engineer
 
Join Date: Jan 2014
Rookie Year: 2014
Location: Hamilton, Ontario, Canada
Posts: 569
nuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond reputenuclearnerd has a reputation beyond repute
Re: Your daily dose of ridiculousness - 775 pro differential swerve

Quote:
Originally Posted by Jjmase123 View Post
Lastly, where do you plan on placing the encoders? You're gonna need 8 of them to control motor RPM, nevermind 4 more if you want real-world angle values from the module's rotation (unless I'm wrong here).
I love to see that others are hard at work on the same idea. There must be something in the HTML on chiefdelphi this summer 😀

You're right that the sketch is missing encoders. I would probably add back shaft encoders to the 775 pros, or perhaps add versaplanetary stages with encoders to the motors. These are both easy, and would plug right into the motor talons.

A third encoder for azimuth is not strictly necessary, but would avoid the need for a homing switch, and might make the control easier. I would probably 3D print a ring gear to attach to the forks, and measure rotation with a third encoder mounted to the bottom plate ( you might get away with only one motor encoder in that case)
Reply With Quote
  #14   Spotlight this post!  
Unread 08-28-2017, 10:14 PM
GeeTwo's Avatar
GeeTwo GeeTwo is offline
Technical Director
AKA: Gus Michel II
FRC #3946 (Tiger Robotics)
Team Role: Mentor
 
Join Date: Jan 2014
Rookie Year: 2013
Location: Slidell, LA
Posts: 4,565
GeeTwo has a reputation beyond reputeGeeTwo has a reputation beyond reputeGeeTwo has a reputation beyond reputeGeeTwo has a reputation beyond reputeGeeTwo has a reputation beyond reputeGeeTwo has a reputation beyond reputeGeeTwo has a reputation beyond reputeGeeTwo has a reputation beyond reputeGeeTwo has a reputation beyond reputeGeeTwo has a reputation beyond reputeGeeTwo has a reputation beyond repute
Re: Your daily dose of ridiculousness - 775 pro differential swerve

Quote:
Originally Posted by nuclearnerd View Post
... A third encoder for azimuth is not strictly necessary, but would avoid the need for a homing switch, and might make the control easier. ...
Three encoders on each module, whether on motor1, motor2, azimuth, or wheel, would provide the redundancy to at least be able to identify the encoder failure you alluded to back in your OP. An encoder on all four axes would provide enough redundancy to dynamically identify and adjust for failure of any one encoder. Of course, you could also use current draw on each motor controller to get more redundancy to be able to accommodate/recognize motor or encoder failure.

Add: This general design reminds me of a helicopter - without smart redundancy, it's just a fancy way to die, or at least throw a match.
__________________

If you can't find time to do it right, how are you going to find time to do it over?
If you don't pass it on, it never happened.
Robots are great, but inspiration is the reason we're here.
Friends don't let friends use master links.

Last edited by GeeTwo : 08-28-2017 at 10:17 PM.
Reply With Quote
  #15   Spotlight this post!  
Unread 08-28-2017, 10:31 PM
nickbrickmaster's Avatar
nickbrickmaster nickbrickmaster is online now
Not Allowed Near Power Tools
AKA: Nick Schatz
FRC #3184 (Blaze Robotics)
Team Role: Leadership
 
Join Date: Jan 2015
Rookie Year: 2014
Location: Eagan MN
Posts: 240
nickbrickmaster has much to be proud ofnickbrickmaster has much to be proud ofnickbrickmaster has much to be proud ofnickbrickmaster has much to be proud ofnickbrickmaster has much to be proud ofnickbrickmaster has much to be proud ofnickbrickmaster has much to be proud ofnickbrickmaster has much to be proud ofnickbrickmaster has much to be proud of
Re: Your daily dose of ridiculousness - 775 pro differential swerve

You need two encoders minimum, one for each degree of freedom, no matter where you place them. If you place them on the motor path, it simplifies the design, but you don't get absolute positioning. You could also modify the design to put them after the differential, measuring azimuth and speed directly. Unless you find a tiny slip ring, you can't make this version coaxial.

IMO a homing switch would make the design simpler.

Also I heard a rumor on Reddit that 971 was working on a differential swerve this summer. No evidence, just rumor.
__________________
I have approximate knowledge of many things.
Any man who must say "I am the king" is no true king.
FRC 3184: 2014-, FTC 10648: 2015-2016
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 10:21 AM.

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