Swerve Drive Idea
 

I'm designing a robot, and have decided to implement a swerve drive. I'm loosely basing the swerve modules on 221's Wild Swerve. These modules have a CIM motor, and gear box on the pod. I would like to be able to turn these modules without any restriction, but those darn wires will get in the way. So, I was thinking of a way to solve this issue, and this is what I came up with.

place 2 stationary metal rings around the module, so it can turn freely, then use pvc, or something to that effect to rout the wires from the CIM to the ring, then attach the wire to a metal wheel and axil assembly (like one on a model train) and use the ring like a track. The ring can then be attached to a Jag/Victor with stationary wires.

This entire assembly, can then be encased in lexan/plastic/something to keep hands away from current.

I would love to here what you think about this idea, any improvements, and/or any constructive criticism

Re: Swerve Drive Idea
 

You're looking for something called a "slip ring."

What you've described is a rudimentary sort, but you can purchase something to do the job as well.

Re: Swerve Drive Idea
 

Bearing in mind they were illegal this year in FRC and may continue to be in the future.

Re: Swerve Drive Idea
 

something like that, but the ones I've seen, wont go around the swerve module, see,

Re: Swerve Drive Idea
 

I seem to have missed this. Under what rules were they illegal?

Re: Swerve Drive Idea
 

This is not a FRC bot, so I'm not too worried about the rules, but I would like to find a solution that COULD be implemented by teams

Re: Swerve Drive Idea
 

They were legal in 08.

Re: Swerve Drive Idea
 

I'll double check this but I do recall reading something about it, I could just be remembering something else.

EDIT: http://www.chiefdelphi.com/forums/sh...07&postcount=3 Al made the comment from a Q&A answer. It says R47 but I don't have a rulebook in front of me.

Yup, and 190 used them well.

Re: Swerve Drive Idea
 

It may be easier to make a hollow main pivot axle so that you can pass the wires out the top of the module.

A few teams did this sort of modification to Wild Swerve units this season.

frc20 is one that comes to mind.

Re: Swerve Drive Idea
 

We did this for our Swerve for Triple Play, and it didn't end well. Eventually the wires will twist and fray, even with programming constraints to avoid as much steering and overturning as possible.

Re: Swerve Drive Idea
 

Agreed, this can be an issue.

I recall frc469 in the past few seasons auto unwinding their swerve modules when they were sitting still to avoid wire issues.

You can always go coaxial. :)

Re: Swerve Drive Idea
 

This is what I'm trying to avoid, I want to be able to make an infinite number of turns, and not have to worry about the wires. I think that by having stationary rings, and in turn, stationary wires, this will prove to be far superior.

I have looked into 118 swerve drive units, but I like larger wheels, and the dual chain drive just seems unattractive to me.

Re: Swerve Drive Idea
 

Team 190 used homemade high power slip rings for their arm in 2008. I believe they worked quite well. If you want more information I can ask someone who was on the team in 2008 to PM you.

Re: Swerve Drive Idea
 

Team 20 had code to center the wheels whenever they are sitting still. They could rotate 1440 degrees total (2 spins either way, limited by the 10 turn pots). We had no noticeable damage to the wires after 3 competitions. We were planning on using magnetic encoders to detect position plus slip rings to have unlimited spins, but that didn't work out.

Re: Swerve Drive Idea
 

This might sound harsh, but if "attractiveness" is a heavy design influence for you, you might want to examine your design expectations...

Re: Swerve Drive Idea
 

I don't mean visually, I mean unattractive in a mechanical sense. I don't like coaxial drive shafts, and extra chain drives that can fail.

Re: Swerve Drive Idea
 

please do, Thanks

Re: Swerve Drive Idea
 

What you are describing is a very common rotary contact device called a "slip ring." There are many forms commercially available. One of the nicest is a mercury filled connector made by Mercotac, which gives noise-free current flow with zero wear. It is true that such slip rings or rotary connectors were suddenly deem illegal this year by FRC Q&A. This was via the response to a forum Q&A on the subject. Our sister team and our team were involved in the questions and responses that brought about this new restriction. We had researched the subject and found that the FRC forum had explicitly allowed their use on six different occasions in the last few years. However when asked about it this year, the response was that they now violated the wiring rules. Turns out in a 2-minute FRC match, with smart, efficient steering logic, infinite rotation in a swerve drive is not really needed anyway. We found that allowing for 4-5 rotations in a wire loop was sufficient. If the steering logic is right, the rotations tend to average out rather than accumulate in one direction. We had a register that tracked the accumulated rotation, and would tend to reverse it if it exceeded a certain limit, but that condition was rarely reached.

Re: Swerve Drive Idea
 

the rule jspatz1 was mentioning that was clarified to us was R50

"<R50> Custom circuits shall NOT directly alter the power pathways between the battery, Power Distribution Board, speed controllers, relays, motors, or other elements of the robot control system (including the power pathways to other sensors or circuits). Custom high impedance voltage monitoring or low impedance current monitoring circuitry connected to the ROBOT’S electrical system is acceptable, because the effect on the ROBOT outputs should be inconsequential."

they just clarified that absolutely nothing besides the copper wires can be used. some members were confused with the clarification and thought of similar ideas, that were still illegal because they would violate the rule.

Re: Swerve Drive Idea
 

Chexposito is totally correct. I should give proper credit to his team 1730 for giving us a heads-up on this issue, and helping us realize that the the rotary connectors were not really essential. Some wire loop and proper programming can handle the problem. (but its not as cool!)

Re: Swerve Drive Idea
 

Do you have to place the motor on the modules?
You can take it off, place it somwhere nice and use belts for both - steering and driving.
Something like that - http://www.chiefdelphi.com/media/photos/35623 , uploaded not so long ago.

Re: Swerve Drive Idea
 

That is a true coaxial design, which I do not believe is what Aaron was after. You're correct that this would allow infinite turns, but I think it is of a different style than what is being discussed.

Re: Swerve Drive Idea
 

That was the method in our module (see pic). Dealing with the connection at the center of rotation is much easier than dealing with it around some perimeter of the assembly. Many rotary contacts are available to connect wires at the center of rotation. Depending on how noise-free you need the connection to be, you may be able to fashion it yourself. Take a look at the rotary connection for the power cord of a typical woman's hair curling iron. Just a center pin in a socket, with another sleeve around the outside contacting a spring loaded contact. The brush contacts to the armature of almost any electic motor is another example. If you don't need a real clean signal, such a simple friction contact may suffice, but if you need a high quality signal such as an FRC CIM would require, I would suggest a commercial rotary contact. The mercury filled type I mentioned earlier worked beautifully on our CIM modules.

Take a serious look at whether you really need infinite rotation in your application. Team 1730 and 1986 learned that you can get several rotations if you route the wire properly, use high-flex wire (high strand count), and give it plenty of slack. We also covered our wire with woven braiding to help keep it under control. The right programming can deal with the rotational limit issue.