Are you curious about crab drives?
Looking to expand your knowledge on swerve drive trains?
Want a chance to discuss the details of making a successful wheel box?
As a late addition to the 2009 FIRST Robotics Conference, The Robonauts will be presenting a session on the evolution of our crab drive wheel box. The official schedule has yet to be updated, but we will be presenting at 8AM Thursday Morning.
Lucien and I will be covering an in depth and technical view of our wheelbox along with justification for many of our teams design decisions. We will share insight from six years of using this crab module and why we’ve settled on the point we are at.
This presentation will be beneficial to any students or mentors who are thinking about building a crab drive. Building a crab drive can be a nightmare to undertake and we want to use this opportunity to help anyone by sharing everything we have learned. We will have wheel modules from our last 5 robots, a slew of spare pieces, and Pro/E models from 6 years of robots for all to play with.
I want to highly encourage team members to attend the Robotics conference, be it our session or any others. This is an excellent opportunity to learn from some of the top mentors and teams in the country. You can never learn too much!
Title: Robonauts’ Crab Drive Wheel Box
By: FRC Team 118, The Robonauts
Abstract:
The Robonauts first implemented a crab drive in the 2004 FIRST Robotics Competition. During each of the past six seasons the crab drive has evolved, resulting in a complex and powerful solution to omni-directional motion. The Robonauts’ wheel box is an infinite rotation module designed with weight, traction, and serviceability in mind. The Robonauts’ wheel box features adjustable steering sprockets for easy wheel alignment along with a coaxial design for steering and power transfer. Knowledge and theory gained from these FIRST robots has been used in the design of NASA’s Lunar Electric Rover. This 7,000 lb prototype vehicle uses six crab modules to effectively traverse a wide array of difficult terrains while carrying astronauts in a pressurized cabin.
Included in the session will be an in depth analysis of design choices and system features of our wheel box. Participants will gain insight into design decisions ranging from bevel gears to bearing selection to machining needs. There will also be a short overview of popular crab drives used by other FRC teams. This presentation will conclude by highlighting the transformation of design from FRC robots to a lunar rover.
I wish I could make it, but I won’t be at Championship this year. Can you guys post the presentation somewhere or make it a CD whitepaper after Championship?
Out of curiosity, how much time does it take for you to assemble one whole module? Our team designed a 3-wheel independently steered crab drive system for the first time this year, which worked surprisingly well for our first attempt. One of the disadvantages was that it was not very easy to maintain. If one part failed, the entire module had to be disassembled, part replaced, and reassembled. In our second to last qualification match the drive motor on our rear module (an RS-545) burned up. As soon as the match ended, our whole team worked as fast as possible to get it replaced. We had about an hour and 10 minutes between matches, and by the time we got the last nut tightened down, our last match had just started and we missed it. If we decide to do crab drive again next year, one of our goals will be to increase serviceability.
Midwest 2007, almost this exact situation happened to us, except ours was a couple loose screws. We had the time and would’ve finished but they decided to run our next match 15min ahead of schedule and as a result we missed our first ever qualification match.
The next swerve only broke once, and took 5 minutes tops to fix that one thing.
Man, I want to go to this. How long will it be, because as the driver/second in command of mechanical department (take that Ryan), I will need to be with the robot most of the time.
I’m going to see if I can get some people not working in the pits on our robot to this. I have no idea if any of our teammates will be “free”, but I think it would be cool if some of our pit recon guys stopped in for a minute.
I really wish I could be there. Instead I’ll be taking a Statics midterm at UT. I’ll be up there friday. Maybe I can swing by your pits and get an impromtu presentation?
You can come by and avoid the large fiasco of 350 teams trying to enter the pits all at once. 8 AM is early enough that you can’t miss practice matches or robot building action.
The 2008 presentation videos and powerpoints are stored on FIRSTs website, so perhaps this year’s presentations will be also.
and as far as recording goes i can bring my equipment to capture it to my computer I just don’t know how it would work because I would need a video feed that I could tap into. If someone who has been to the conferences before could tell me more about how its setup as far as recording goes I would be very grateful
I’ll be there. We have some great ideas to try to revolutionize what FRC drive trains are seen on the field, and a couple of them require crab modules. I’m finalizing some research, etc, and have some (hopefully) pretty specific questions that will either be very easy or hard to answer. I also like how the focus of this conference is on the ‘why’ of the decisions rather than the specifics of ‘what’ for each decision.
Thanks to all that attended. Lucien and I were absolutely stoked that so many showed up. We really hope that we were able to answer some of your questions. Our only regret is that we weren’t able to manage our time very well. It would have been great to keep chatting before Andy Baker kicked us off the stage for his presentation. =)
One follow up question that I was asked a number of times over the weekend (by whom I don’t remember) was what we used for our bevel gears. They are 15 tooth, 12 pitch miter gears from McMaster. The part number is 6843K13. Sorry I couldn’t answer you on the spot, but I hope this information finds those inquiring minds.
I’m sneaking the module plate that was handed out into our next batch of powdercoating. Maybe that will convince the next batch of mentors to do crab, and to do the right way
