Swerve drives

[bbradf44]

With the majority of our team graduating this year(about 80%) a couple of us have been thinking about doing one last project in the off season as a team(if we can get the mentors to bite) to both leave something behind that the younger guys can improve on in the coming years to maybe get on a competition bot by the time the current freshman are seniors and to teach them all that we've learned from our experiences. The idea of a swerve drive was brought up but immediately shot down, but then brought up again with some ideas. Sense then we have done some drawings and Inventor projects(nothing worthy of posting here) and are thinking it may be possible. Because we aren't a very high budget team our design will differ greatly from things you'd see on Einstein now but actually don't look half bad modeled out in inventor. My question here is what are some of the most interesting swerves you've seen? Working/not working, on/off a competition not. Post pictures or videos as well.
Also as a side question. I wasn't able to do much pit scouting the past 2 years at Peachtree as I've been stuck in our pit, but I've always been fascinated by swerves and told our pit scouts that if anyone says they have a swerve to come get me immediately, and I've never been told of any. Have there been any teams here in Georgia to pull one off yet?
Thanks!

[Foster]

There are a number of teams that have swerve drives (Not sure about Georgia). Most of the teams have posted decent pictures. 1640, Sab-bot-age has pictures, CAD, etc of the last 4 years worth of swerve drives. It would make a good place to start since they have done a good documentation trail of what worked, what didn't, where they made improvements, etc.

Swerve isn't for the faint of heart, but is amazingly cool when it works.

Sab-bot-age Team Site Swerve Central

[Jay O'Donnell]

Here's team 2067's swerve drive info. Only swerve drive in New England that I know of and they really used it well this year! http://www.chiefdelphi.com/forums/sh...highlight=2067

[Bryce2471]

Here's a link to a thread on team mean machine's swerve drive. The most recent BOM counted them at $221 each, so you may want to consider a similar design.

http://www.chiefdelphi.com/forums/sh...ht=2471+swerve

There are a few other threads on them, if your interested. Hope that helps!

[Tyler2517]

It is possible to obtain outside funding for the production of a swerve drive. This year we got a grant just for the production of ours.

2471 has an amazing swerve drive that is both light and cheap to manufacture. Making the top out of one piece of extrusion is a great idea. The gear box they use for steering is much cheaper then any thing else i have seen and worked amazingly.

Team 1640 has a lot of info about the history of their drive train. Also a great team who does well with it.

Team 16 has a legendary swerve drive. They don't use a Co-axel design but acts as if they were by using slip rings.

We ran a swerve drive this year as well. We used a cool concept that a student from 2471 thought of(the long tube with the drive belt running around the steering motor). Along with a modified version of 1640's bottom pivot/yoke. We redesigned how to build it to make as many parts of it manual machined on a mill/layth.

[Gdeaver]

Ok, for the teams that did swerve for the first time this year, was it worth it. Do you feel that it gave you a competitive advantage?

[kylelanman]

Originally Posted by Gdeaver

Ok, for the teams that did swerve for the first time this year, was it worth it. Do you feel that it gave you a competitive advantage?

YES!!!

We decided day 2 of the build season we were going to go with a swerve drive. The general decision making paradigm was that due to the lack of a crazy pyramid to climb or any end game for that matter the rest of the robot was not going to be that complex. Therefore we thought we would have enough time to figure out a swerve drive. Having never done one before we reached out to a new company in the area for funding so we could build 2 drive trains. One was built the first week and given to the programmers and the second became the actual robot. We bought 118 style swerve modules from AndyMark and wrote the code from scratch. We did reference 16's code base to ensure we were on the right track from time to time.

We firmly believe and demonstrated in Wisconsin that our swerve drive gave us the additional competitive edge needed to win. The extra agility that the swerve drive provided allowed us to play very effective defense and quickly out maneuver our opponents to score. We took a gamble and it paid off with our first blue banner ever.

[Bryce2471]

Originally Posted by Gdeaver

Ok, for the teams that did swerve for the first time this year, was it worth it. Do you feel that it gave you a competitive advantage?

Yes,

We did some off-season development of swerve drives, and we were very glad that we did. We already had the code nailed down, and enough swerves for the practice bot, so we just adjusted the design slightly, and pumped out six more for the comp bot. They have had great performance overall, and have had no mechanical failures!(knocks on wood)
One thing we have been displeased with is the optical encoders. The ones we use have an index pulse, but can still get off by a significant amount for a noticeable portion of the match. Unless we stop to run a homing routine.
We are testing magnipot absolute encoders from Digi-Key on the practice bot and we will probably be changing out the comp bot's encoders for them at champs.

[Gdeaver]

I like the 6127's. We did have problems losing calibration. We used plastic beam couplers from Automation Direct. They would some times slip requiring calibration. This year we took advantage of the good AL beam couplers that were on First Choice and they do not slip.

[bbradf44]

Heres a couple images of our inventor creation. Its still missing the gears, chain, axles, and belts but this is the basic design. This is only a rough and dirty concept. Below the piece of wood is the lazy suzan bearing. about 1/2 inch above the wood is a sprocket for the turning

[Bryce2471]

Originally Posted by Gdeaver

I like the 6127's. We did have problems losing calibration. We used plastic beam couplers from Automation Direct. They would some times slip requiring calibration. This year we took advantage of the good AL beam couplers that were on First Choice and they do not slip.

Ours were really easy to set up compared to the USD encoders we were using. We thankfully decided to get the fattened shaft version. This means that the setscrew we use to pin them down will not slip, and we don't have to find the junction between 0v and 5v on each one individually. We know that when the flat of the shaft is facing towards the BI symbol of the encoder, it is at "zero". We then mount them to the drive so that when the encoder is at zero the set screw is accessible. We then turn the module to a 45 degree angle,(witch is where we used to put the index) and slide on the plastic encoder gear.

We haven't done extensive testing, but the process seams promising.

PS. How do you interface with the output pins on the 6127's? We just solder PWM cables to them.

[ekapalka]

I'm not sure if this is true or not, but I've been told that a good thing to use for swerve drives are ten-turn potentiometers. The benefit being that you can easily plug it into the following

angle=(potentiometer_voltage-inherent_zero)*voltage_to_degrees

to get to the angle, whereas with other potentiometers you need to account for some sort of wraparound

[Orion.DeYoe]

Swerve is something I've wanted to build in the offseason for a while. I understand the mechanical and control concept of it and I know how it's driven and mostly how the modules need to be constructed.
The point that I have a really hard time understanding is how the pivot is set up. Does it just ride metal on metal? Or is there some sort of bearings, rollers, or slip pads/blocks? How do you contain the rotating module (the yoke) up and down and side-to-side while still being able to disassemble it? No one seems to have any good cross section views of the modules in an assembled state.

[The Doctor]

Originally Posted by ekapalka

I'm not sure if this is true or not, but I've been told that a good thing to use for swerve drives are ten-turn potentiometers. The benefit being that you can easily plug it into the following

angle=(potentiometer_voltage-inherent_zero)*voltage_to_degrees

to get to the angle, whereas with other potentiometers you need to account for some sort of wraparound

Team PWNage was using a $60 Absolute value encoder to figure out the angle.

[Jefferson]

Originally Posted by ekapalka

I'm not sure if this is true or not, but I've been told that a good thing to use for swerve drives are ten-turn potentiometers. The benefit being that you can easily plug it into the following

angle=(potentiometer_voltage-inherent_zero)*voltage_to_degrees

to get to the angle, whereas with other potentiometers you need to account for some sort of wraparound

If you are using the WPILib PIDController, it's as simple as setting the PIDController to continuous when using a continuous rotation encoder/potentiometer.

You have to keep up with turns and unwind if you get close to the limit on a 10 turn pot.