Disadvantages of swerve/crab

[thefro526]

Originally Posted by Leeland1126

Swerve is so much desired because it offers the omni-directional movement of Mechanums, without relying on wheel slip and thus, is not as easily pushed. However, that in no way means the average Swerve can push. Your standard 4 wheel Swerve will lose a pushing match against most decently done 6 Wheel Drive Systems.

In addition, Swerve won't outrun a lot of drive systems. It's going to rely on that omni-directional movement to cut out the time used in turning to make up for the lack of excessive speed. Unless you're 973 using Emperor Swerve, you're not going to be moving at very fast speeds.

These points aren't necessarily 100% accurate. Both of these will vary with the implementation of the swerve and the drive it's being compared to.

Pushing power is defined by the robots over all weight and wheel configuration, being a swerve doesn't really change much here - other than the fact that a 'unicorn swerve' (or any swerve with independently powered modules like 111's) has the issue of losing pushing power if one or more of the wheels lose the ground as the motor's power is wasted and the weight on the driven wheels will now be less - this is an issue that any drive with independent wheels can encounter.

For examples of fast swerves other than 973's Emperor Swerve, reference either 16 (In any year, but 2008 or 2011 would be best) or 148 (2008).

[Akash Rastogi]

Originally Posted by thefro526

These points aren't necessarily 100% accurate. Both of these will vary with the implementation of the swerve and the drive it's being compared to.

Pushing power is defined by the robots over all weight and wheel configuration, being a swerve doesn't really change much here - other than the fact that a 'unicorn swerve' has the issue of losing pushing power if one or more of the wheels lose the ground as the motor's power is wasted and the weight on the driven wheels will now be less - this is an issue that any drive with independent wheels can encounter.

For examples of fast swerves other than 973's Emperor Swerve, reference either 16 (In any year, but 2008 or 2011 would be best) or 148 (2008).

In addition to this- you (leland) keep saying "your standard swerve drive" but what are you defining that as?

The pushing thing can be whatever depending on the drive gearbox just as any other drivetrain can be. 2 speed solves all problems you mentioned.

[Chris is me]

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

[sgreco]

Originally Posted by Chris is me

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.

[craigboez]

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.

[Lil' Lavery]

Originally Posted by craigboez

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.

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

[Akash Rastogi]

Originally Posted by craigboez

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.

What is impractical about making a multi-speed swerve?

[AlexH]

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.

[Mk.32]

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.

[Aren_Hill]

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

[craigboez]

Originally Posted by craigboez

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.

[Chris is me]

Originally Posted by craigboez

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...

[AdamHeard]

Originally Posted by Chris is me

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.

[craigboez]

Originally Posted by Chris is me

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.

[Garrett.d.w]

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.