Chief Delphi - Crazy Crab

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- - Crazy Crab (http://www.chiefdelphi.com/forums/showthread.php?t=75419)

Yeah I would also love to go to the meeting but I am wondering if its an official conference too.

I had entertained the thought of making a crab drive. Here are a few of my cad files.

Unfortunately I have no idea where the files are for these. But you can get the general idea as to how to do this

Is there any updates on the swerve meeting?

Quote:

Originally Posted by Fe_Will (Post 846749)

I was thinking of starting a new thread but I'll just ask this here:

Can people/teams with actual crab/swerve experience post some info on:

what the pros & cons of controlling the 'cans':
individually vs left/right vs front/back vs all together

and/or

what the pros & cons of powering the wheels:
individually vs left/right vs front/back vs all together

Our team is also interested in prototyping this type of drive over the summer, we know the basics but not the advanced control part:D

(and yes I spent 4 hours going through the pictures/threads that are on CD) :cool:

No I do not have experience with this drive train but I would like to make a suggestion, instead of relying on other team's advice for the front/back vs left/right comparison why not do it yourself if you decide individual is not for you? It is rather simple to change a practice chassis from left/right to front/back. The only change is coding, and that could be done using an offset to the wheel angle.

And on an unrelated note, as a programmer I second the opinion of design in sensors. For reference, programming, while it appears magic to some, is actually not magic. ;)

I would suggest that if your team attempts crab/swerve, get high quality sensors, and put them in the CAD. It would be really horrible to be stuck with wheels that you don't know where they are.

I know that for our crab/swerve, we had a front/back steering. Whole system Power. It worked great.

I don't know the sensor that we used, but it was a magnetic sensor, and according to our programmer called an "angular position sensor"

Try to make the sensor rotate the same amount as the wheelboxes, otherwise the math gets harder.

And for chain, we used #35 chain, but if we do crab/swerve again, we are going to try and use #25 chain, because we had somewhere around 30 feet of chain in our system. Just for drivetrain.

With this much chain, I became very adept at breaking and rebuilding the chain.

Quote:

Originally Posted by Andrew Schreiber (Post 850764)

There is a huge difference in the cost/time/design of an individual 'can' control set up vs. a front/back or a left/right one vs all together. I would like help evaluating the pros and cons of these so that my team can make educated decisions with our resources. Now if you are interested in providing resources I am more than willing to spend them 'trying it out'.

1's and 0's are cheap for the most part but, when it comes to building a quality prototype I prefer to have a clear understanding of what I'm doing...

Don't do it individually. You can do it front/back, left/right, or all together. But not individually. Why? One sensor goes on the fritz and suddenly you can only drive in circles or straight lines.

Can you do it? Yes. But you may easily wind up with something like:

|.......\

|........|

or some other combination that has one misaligned wheel. That's probably the #1 reason that most teams go L/R or F/B or all together.

If L/R or F/B gets misaligned, it's easier to reorient the other side and drive tank for a bit until you get a chance to replace the sensor or whatever failed.

If you do go individual orientation, you are also taking 4 extra motors away from other things. For any crab, you're talking a minimum of 2 (1 motor to turn, 1 to drive). However, most use 5-6.

I know I'm doing a minor thread revival, but I'm entertaining the thoughts of a crab drive. I've read through the entire thread, and I've seen a lot of seemingly complicated ideas for crab. Is there a possibility of having one motor control the turning, and then one motor per wheel? Most of the CADs put up were modular, and the idea of having tank-like crab goes over my head.

http://s15.photobucket.com/albums/a3...ent=crabby.jpg

Something like that. (Sorry about its crudeness, I haven't quite gotten the hang of inventor yet.)

My team is wanting to have a crab drive system also, so if anybody could help us that would be great :)