Crab Drive HELP!!***

Ok, this is a huge issue on my FRC team. Many of the other team mates (including myself) want our robot to have a crab drive system on it, but some of the other members are opposed to this idea because it is well…new and they have no clue as to how they are going to build something like this.

Can someone please help me out and point me in the right direction as to where I can find some drawings or parts? Thanks in advance.

Search the white papers here, also google Crab Drive, especially Wildstang’s site.

Crab sounds like a great idea, but if you’ve never implemented one before, be advised it’s not as easy as it looks. Most teams successful with it built a prototype between the end of the last season and the beginning of the next season - 8 months? - and learned how to make it work while there was no time pressure. Your team might consider this approach.

One point: NASCAR doesn’t use crab drive, why does your team think it needs to? Examine that question, and the answers might surprise you.

Don

Do a little research here at ChiefDelphi. I know there are tons of people willing to help, and they have had some of the same problems as you. I would also recommend doing a search on google, or similar search engine. I would personally suggest a mecanum are omni wheel drive, as they are easier, more reliable, and you should be able to find more info on those drive trains.

I agree with Don; if you haven’t already built a crab/swerve or have a really solid idea of how to do it, don’t. Crab/swerve is probably the most mechanically complex drive system you could try, and the software is even worse. I also agree with Tyler, mecanum is probably the simplest way to a omni system, but it still will require significant amounts of research. The bottom line is, do you want to spend six weeks on a drive system that you’ve never tried before and risk completely failing, or do you want something tried and true that can be complete by week two (or even before, depending on shipping times)? If you;re adamant on using an omnidirectional system, the PowerPoint on them at the FIRST Robotics Canada Resources Site would be a good start.

I would also recommend looking at the Chief Delphi Media pages. There are very detailed designs of crabs that you may want to incorporate.

Here’s the link:
http://www.chiefdelphi.com/media/photos/tags/crabdrive

Good advice but the good thing about a mecanum drive is if you can’t get it to work you can always put on regular wheels and drive.

the crab drive is a useful thing to have and as far as pictures go look at either 1086 or 384 robot from last year

Because of the hundreds of rules that don’t allow drive systems not sold on production cars? Maybe?

Anyway, if you haven’t built a crab before, or spent months designing one, you’re way behind. Good luck building one, if you can.

Yea I have to agree you are behind, but that shouldn’t stop you from trying you can always go to a standard tank drive or even only a two wheel crab with omnis in the back (teams have used this effectively before) if things don’t go your way.

Check out Team 118
http://www.robonauts.org/
They are a Great Bunch of guys and would be happy to advise you. They have been using a crab drive for several years and have developed a fairly complex system. They may tell you you’re in over your head but at least if they do, you’ll know it’s true.

Good luck!
Steve

I will echo what everyone else has pretty much said, check out the mecanum drive as it’s probably your best bet for what you’re looking to achieve in a short amount of time. It’s no easy task, but it’s easier than other omni-directional drives. My opinion of this year’s game is that if you can create a very slick, very well practiced and smoothly operating mecanum drive, you’ll have a significant advantage. Be prepared to put in a lot of time though.

Can’t this team just use the Andymark Mecanum drive that is available as a COTS item?
Fabrication time of the drive wheels themselves would essentially be nothing at that point, (minus some obvious separate assembly time) and then it’s just a matter of waiting for it to be shipped to you, mounting it on the robot, and then having drivers practice with them.

Am I missing something here with my suggestion? :confused:

As I remember it, both teams used mechanum drive, which is totally different than swerve.

If you are planning to build a swerve AND a hurdling mechanism… Good Luck… I certainly wouldn’t undertake it…

But if you just want to focus on herding the balls and quickly moving around the track why not? If your drive train is the only thing your building this season why not do something sophisticated like a swerve?

If you do decide to undertake a swerve/crab design make sure to spend a little extra time in the design process to build in a back up plan; Make you can switch the crab/swerve into just a normal 4WD in case it doesn’t work out. This way you at least have a driving base in case of failure and won’t be stuck with a completely disappointing season.

I’d say go for it if you have you have a reasonable amount of resources; you miss 100% of the shots you don’t take.

Sort of. As you pointed out, a basic mecanum isn’t that mechanically challenging (although a suspension might be very important to have, depending on your frame). The software, however, can be rather tough. Not an insurmountable problem by any means (as all the mecanum robots proved last year), but it can be troublesome; just figuring out how to setup the controls for the driver can take a good bit of time.

GGCO,
Although crab drive is a great tool we don’t use it all the time. It will only be incorporated into the robot design after careful consideration and playing the game. Don’t make the decision at this point, play the game using chairs or tricycles or whatever and see if it is needed. If the team decides to use it then be advised that crab requires some strong mechanical attachments for both the top and botom, special handling to determine how assemblies are attached for steering, how to build a module so that both the wheel and the motor you use will fit into the space you require for turning the module and realize that crab by design puts the wheels closer to the center of the robot which compromises stability. After all of that is overcome, your drivers still need plenty of practice.
A so-so robot with lot’s of practice will beat out a superior robot with no practice, every time.

As a personal request, can you include your first name in your profile? It makes it easier to respond. Thanks.

Ok, thanks all for replying! I am doing research and I am starting to see that a well designed robot/crab drive is not going to happen. I’ll try to convince the rest of the team. THANKS!

My team had a crab drive system last year. It worked great and for the game this year it should be good for going around… you dont even have to turn.

But it probably would not be good for hurdling… Its best use could most likely come from herding the ball around with it