Disadvantages of swerve/crab

[LeelandS]

Originally Posted by Akash Rastogi

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.

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.

[thefro526]

Originally Posted by Leeland1126

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.

Not a problem, your unclear term usage inspired quite a bit of good discussion.

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.

Doesn't address the software though...

[Akash Rastogi]

Originally Posted by Leeland1126

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.

Originally Posted by thefro526

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.

[Aren_Hill]

Originally Posted by davidthefat

Complexity of the hardware.

Ignoring the original posters statement?

Originally Posted by MICHAELABICK

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...

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.

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)

Originally Posted by 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.

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

[Ether]

Originally Posted by Akash Rastogi

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.

In the above context, "the best controls" sounds like you are referring to the driver interface. What driver interface did you finally decide was the best for your team?

It is a HUGE learning curve for even the best programmers. (we had students and programming mentors working on it)... 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.

Could you elaborate just a bit and list the top three (or whatever) things that made the learning curve huge and which took a long time to figure out? It might be helpful for other teams on the verge of making a similar decision.

[Akash Rastogi]

Originally Posted by Ether

In the above context, "the best controls" sounds like you are referring to the driver interface. What driver interface did you finally decide was the best for your team?

Sure thing! Best is the wrong word too, "better" is the correct choice. We started off with a single 3D Pro joystick to control the drive system, but did not get a chance to figure something else out until later in the season which was using a joystick for throttle and then used the 3d joystick for rotation. It isn't best, but it was as far as we got before we decided to put off swerve until future offseason projects. But even then, we ended up using the override button on the joysticks which turned it into a 4 wheel tank drive most of the time.

Originally Posted by Ether

Could you elaborate just a bit and list the top three (or whatever) things that made the learning curve huge and which took a long time to figure out? It might be helpful for other teams on the verge of making a similar decision.

I'd say some of the biggest issues we had were 1. being dumb and not using a 1:1 reduction for the rotation, 2. getting the modules perfectly synched, and 3. realizing too late that we should have used higher quality sensors than we did.

Big problem was that our drivers expected a perfect response time from the modules everytime they wanted to move somewhere, but our gearing and sensors significantly delayed response time.

Originally Posted by Akash Rastogi

Big problem was that our drivers expected a perfect response time from the modules everytime they wanted to move somewhere, but our gearing and sensors significantly delayed response time.

How significant? Was it like major lag between controller input and movement, or more like a small yet noticeable change between input and movement?

Also, what gearing did you use, and which sensors? Which would you recommend of both?

[Akash Rastogi]

Originally Posted by SuperNerd256

How significant? Was it like major lag between controller input and movement, or more like a small yet noticeable change between input and movement?

Also, what gearing did you use, and which sensors? Which would you recommend of both?

It did what seemed liked a small change between input and movement sometimes, but later on that was fixed. The delay later on was, to me, significant because I did not know what to expect. It was just not instant as we all wanted, and I think this also happens to a lot of people when they first try swerve. The team might be under the impression that they'll get prefect turning and response from the get-go. However, with optimized systems such as 973, 111, 16, I suspect they see the kinds of results we expected: instant response (or close to).

As for the gearing, I'd have to go back to the CAD as I don't recall. The CAD should be somewhere on the Autodesk website from 2010 if they still archive that stuff.

[sgreco]

Originally Posted by Akash Rastogi

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.

That's actually pretty quick as far as I'm concerned. 2079 built a prototype swerve before the 2008 season, we build a swerve drive for the 2008 season. We made our third iteration for the 2009 season. We just started to get it where we wanted it at the end our second regional in 2009. They have since ditched the idea of swerve do to complexity and lack of a fully intuitive algorithm for controls.

The real thing is that swerve is just harder to make well. It's not better or worse than any other drive train.

[John]

Theoretically, if you had unlimited resources, unlimited manufacturing time, unlimited programming time, and unlimited driver practice time, to build a "perfect" swerve drive, it would be clearly better than any other drive train. I would consider a "perfect swerve drive to be: all wheels independently powered, steered, shifting, never breaks , low weight, very low delays in turning the wheels, driver can intuitively control all functions, no repercussions on other systems.

Its pushing strength would be as good as a low speed skid steer,
its speed would be as good as a high speed skid steer,
its acceleration would be as good as any robot of similar weight,
its omnidirectional ability would be as good as mecanum/omniwheel drive

However, any real team does not have unlimited resources and time. As a result, most swerve drives do not achieve that performance. Some teams have gotten close, and these teams have generally been very successful, (148 in 2008, 111 in 2009). The problems with a swerve have to do with the real challenges of making one work like it is supposed to without massive tradeoffs, and not with any inherent disadvantage to swerve.

[Ether]

Originally Posted by John

Theoretically, if you had unlimited resources, unlimited manufacturing time, unlimited programming time, and unlimited driver practice time, to build a "perfect" swerve drive, it would be clearly better than any other drive train.

You didn't mention anything about waiving FRC rules, so I assume you are still limited to the legal type and number of motors.

its omnidirectional ability would be as good as mecanum/omniwheel drive

I think the jury is still out on whether it is possible to steer the wheels on a swerve fast enough to make swerve "omnidirectional ability" as good as a well-built omni or mec.

[Siri]

What Jared said.

Also, FIRST has literal strategies that jack-of-all-trades swerve just isn't the best for. Of course, if you want to master a single "trade", swerve isn't necessary. But even if you want more, swerve gives you two things--reasonable holonomic-ness and reasonable traction--all the time. If you want, say, better holonomic drive sometimes and unmovable traction other times, something like switchable wheels/Octocanum could be better. Etcetera.

Originally Posted by Akash Rastogi

What is impractical about making a multi-speed swerve?

Depends. If you're doing a limited swerve/non-coaxial, adding a shifter isn't so hard. Maybe heavy, but at least you're not rotating it and probably don't need so many. In a co-axial, you're driving each wheel independently and rotating the drive motor/gearbox with the module. Adding a shifting mechanism gets really big and heavy (and expensive and complicated) really quickly. We do all our gear ratio adjustment via belt pulleys and planetary gearboxes. After two years of working on the drive, "impractical" still seems like a pretty good word for trying to mount an AM Supershifter on this, but maybe there are more streamlined shifters?

That said, we tend to win our pushing contests.

Originally Posted by AlexH

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

Moreover, only if you have enough good drive time with your chassis to get this capitalization experience. We've done poorly in this area for the first two years, but now that we have essentially optimized hardware, getting-close programming and excited drivers, this is huge.

Originally Posted by Aren_Hill

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

Wow, that's great! Our modules are at 9.1lb each with a 14.1lb chassis weldment. How'd you get it to 35lb total?

[gblake]

One obvious disadvantage is the endless debate they engender.

One clear advantage is the endless debate they engender.



Blake

[Aren_Hill]

Originally Posted by Siri

Wow, that's great! Our modules are at 9.1lb each with a 14.1lb chassis weldment. How'd you get it to 35lb total?

Well over thanksgiving I rebuilt 1625's 2010 practice chassis (was 6wd swerve) into an 8 motor independent swerve, that came in a 41lbs,

Mainly its just sitting there staring at a concept going "how do i get rid of that....and why is that even there?" when looking at parts

current one i have almost ready to go is 6lbs flat per module (including CIM and steering motor)

[Siri]

Originally Posted by Aren_Hill

Mainly its just sitting there staring at a concept going "how do i get rid of that....and why is that even there?" when looking at parts

current one i have almost ready to go is 6lbs flat per module (including CIM and steering motor)

That's awesome! Great job. Do you have CAD or photos?