Swerve Drive Idea

[The Analog]

Originally Posted by CraigHickman

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

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.

[The Analog]

Originally Posted by Dave McLaughlin

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.

please do, Thanks

[jspatz1]

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.

[Chexposito]

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.

[jspatz1]

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!)

[Mori1578]

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.

[Dave McLaughlin]

Originally Posted by Mori1578

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.

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.

[jspatz1]

Originally Posted by ajlapp

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.

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.