Chief Delphi - Disadvantages of swerve/crab

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Re: Disadvantages of swerve/crab

Quote:

Originally Posted by Chris is me (Post 1094430)

How many of you guys have built and tested a swerve and compared it to a six wheel?

2079 has kind of done this. We didn't really test any quantitative data, but we have run both in comparison during driver tryouts. The general sentiment from our drivers was that swerve is not as intuitive to drive (it does depend on the programming, but the programming is something that is really hard to get right).

And just from experience of doing both, 2079's 2nd gen swerve broke with much higher frequency than our 1st gen 6WD. Swerve requires a lot more fine tuning before you get it "right".

All 6 wheel drives have a zero turn radius (or at least most). Only well designed swerve drives can do this.

Both designs are good if implemented well, swerve just seems to require more effort to make it work well.

Re: Disadvantages of swerve/crab

I'd say one big disadvantage is that it isn't very practical to implement a two speed drivetrain with swerve. You'd need to pick one multi purpose speed and gear for that, making your robot prone to being pushed around by a 2-speed 6WD bot.

Re: Disadvantages of swerve/crab

Quote:

Originally Posted by craigboez (Post 1094447)

Well, if we're ignoring the weight and manufacturing factors as instructed in the first post... :rolleyes:

Re: Disadvantages of swerve/crab

Quote:

Originally Posted by craigboez (Post 1094447)

What is impractical about making a multi-speed swerve?

Re: Disadvantages of swerve/crab

They eat a larger chunk of the weight budget than a normal tank drive.

Only effective if you have a good driver who can capitalize on the directional freedom that a swerve offers.

Re: Disadvantages of swerve/crab

The extra driver practice it takes to be able to master a swerve and be able to use all its features, though personally I have never done it so I can't speak from experience.

Re: Disadvantages of swerve/crab

The largest disadvantage I see to a swerve (once constructed and programmed) is it takes more driver practice to get to the same level as a 6wd, and then eventually surpass. Most silly humans get a little overwhelmed by the ability to go anywhere and spin any way.

sincerely,
someone with actual swerve credentials, who's spent the last few days driving around a unicorn swerve

Re: Disadvantages of swerve/crab

Quote:

Originally Posted by davidthefat (Post 1094409)

Complexity of the hardware.

Which is nothing compared to complexity of software/control philosophy.

Re: Disadvantages of swerve/crab

Quote:

Originally Posted by Leeland1126 (Post 1094434)

Apologies, I'm being quite unclear about these things right now.

By "Standard swerve", I'm not referring to anything particular about the Swerve itself. I'm referring more to a Swerve from a team who hasn't really mastered the Swerve yet (i.e. 16, 111, 118, etc.). Those teams have worked up good implementations to Swerve, and have made steps in overcoming the common short comings that go with it.

Again, I apologies. I'm being very unclear.

No need for apologies, I was just wondering what people consider a standard swerve to entail.

Quote:

Originally Posted by thefro526 (Post 1094438)

Also, it's worth mentioning that a team could build a 'fast' (Relative term), 'powerful' (Relative term), swerve using proven COTS components from AM and Team221 LLC - they've done the hard mechanical work for a team looking for swerve performance without swerve machining resources.

Just an anecdote of caution:
Using the 221 modules in 2010 was pretty cool; we learned a lot about the mechanics of a swerve. But with only a week to figure out how to program the swerve - our team just made an idiotic decision to go with this drive over our 8wd design, even after we were told we wouldn't get our modules until after week 3. This stupid decision was made because students and mentors got entranced by the "coolness factor" of swerve. It had no place in the 2010 game. Even with a full practice swerve to play with and program, we had only just started to figure out the best controls for the swerve WHILE in Atlanta that year. It is a HUGE learning curve for even the best programmers. (we had students and programming mentors working on it). All I'm trying to say is that even with the mechanics pretty much figured out for us through COTS parts, the programming and sensory involved took a long long time to figure out. It is hard to express my abhorrence for the decision making that went on that year.

Re: Disadvantages of swerve/crab

Quote:

Originally Posted by davidthefat (Post 1094409)

Complexity of the hardware.

Ignoring the original posters statement?

Quote:

Originally Posted by MICHAELABICK (Post 1094411)

Simply, there is none. An independent coaxial swerve, programmed perfectly, will be the best drive out there. The one performance disadvantage, is that if one module brakes, your whole drive system is down

Oh really? lost a drive chain on an 8motor swerve to one of the modules recently and kept on driving just fine, barely noticed...

Quote:

Originally Posted by craigboez (Post 1094447)

One of the largest Pro's to swerve is almost never having to get into pushing contest you don't want to, in many cases rendering 2 speeds not necessary. (keep in mind i had a 2 speed swerve in 08, using COTS AM gen2's....so the 2 speed part really didn't require much work on my end)

Quote:

Originally Posted by AlexH (Post 1094460)

They eat a larger chunk of the weight budget than a normal tank drive.

Only effective if you have a good driver who can capitalize on the directional freedom that a swerve offers.

I've got a few concepts that could hit < 35lbs for complete chassis with completely independent module power and steering, so weights only really an issue if you aren't trying hard enough

Please only post things when you KNOW them, preferably from experience, or as some have done, put a proper disclaimer

Re: Disadvantages of swerve/crab

Quote:

Originally Posted by craigboez (Post 1094447)

I'd say one big disadvantage is that it isn't very practical to implement a two speed drivetrain with swerve.

Should have clarified, it is impractical if you're using 4 wheel swerve with one CIM at each wheel. If you're using a central "power plant" then it becomes much more practical.

Re: Disadvantages of swerve/crab

Quote:

Originally Posted by craigboez (Post 1094482)

Should have clarified, it is impractical if you're using 4 wheel swerve with one CIM at each wheel. If you're using a central "power plant" then it becomes much more practical.

973 just posted a neat little CAD model of an 8 motor independent shifting swerve...

Re: Disadvantages of swerve/crab

Quote:

Originally Posted by Chris is me (Post 1094484)

973 just posted a neat little CAD model of an 8 motor independent shifting swerve...

Yup.

Any team with a manual mill and a waterjet/laser sponsor could make such a thing as well.

Most teams are capable of getting such sponsors and machines.

Re: Disadvantages of swerve/crab

Quote:

Originally Posted by Chris is me (Post 1094484)

973 just posted a neat little CAD model of an 8 motor independent shifting swerve...

Wow, very impressive. I didn't think that was practical, but they went and proved me wrong.

Re: Disadvantages of swerve/crab

As has been said earlier, driver practice is the main bump in the road (so to speak). If you plan on building a swerve drive, prototype it in the offseason. We didn't, so even though our swerve worked perfectly, we modified it to drive like a tank.

As with everything, practice makes perfect.

I wish you luck if you decide to go for it. It's one of the coolest drive systems out there.