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Unread 08-06-2017, 05:51 PM
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Slip Rings

Looking for 12 awg slip rings suited for FRC. Also, posts from teams who have successfully created them on their own as a custom circuit.

Thanks!
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Unread 08-06-2017, 06:01 PM
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Re: Slip Rings

Team 190 had a slip ring as a custom circuit in 2008. Not sure if it would be legal now. I believe it was 6 wires powering 3 different motors.

I didn't have anything to do with building the robot and don't have any pictures at the moment but you might be able to find something.
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Unread 08-06-2017, 06:08 PM
ngreen ngreen is offline
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Re: Slip Rings

I've seen these come up for this question before, but don't have experience with them: http://mwands.com/store/180-amp-6-wire-slip-ring
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Unread 08-06-2017, 06:23 PM
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Re: Slip Rings

Quote:
Originally Posted by ngreen View Post
I've seen these come up for this question before, but don't have experience with them: http://mwands.com/store/180-amp-6-wire-slip-ring
Yes these come up a lot. I think some teams have used them too. The main issue is that they have 6 contacts rated for 30A each so you will have to split wires and have 2 + and 2 - terminals (and 2 CAN?) which is a bit janky for inspection. Just be cautious that's all.
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Unread 08-06-2017, 06:42 PM
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Re: Slip Rings

Quote:
Originally Posted by pkrishna3082 View Post
Yes these come up a lot. I think some teams have used them too. The main issue is that they have 6 contacts rated for 30A each so you will have to split wires and have 2 + and 2 - terminals (and 2 CAN?) which is a bit janky for inspection. Just be cautious that's all.
It's not just janky for inspection, it's not legal on a 40A circuit.

Quote:
R58. Branch circuits may include intermediate elements such as COTS connectors, splices, COTS flexible/rolling/sliding contacts, and COTS slip rings, as long as the entire electrical pathway is via appropriately gauged/rated elements
There's no provision at all in that rule for splitting the current across two connectors instead of just one in order to meet the rating.

If you use that specific slip ring, you'll need to run it off a 30A circuit or less.
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Unread 08-06-2017, 06:52 PM
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Re: Slip Rings

Quote:
Originally Posted by Jon Stratis View Post
It's not just janky for inspection, it's not legal on a 40A circuit.



There's no provision at all in that rule for splitting the current across two connectors instead of just one in order to meet the rating.

If you use that specific slip ring, you'll need to run it off a 30A circuit or less.
There is precedent (disclaimer about previous year rules not being applicable next year) https://www.chiefdelphi.com/forums/s...1&postcount=28

Quote:
Originally Posted by RyanShoff
We've used those same slip rings in 2015 and 2017. Each time we used 3 legs in parallel. I dissected a used one and saw no noticeable wear.

We asked Q&A question 85 in 2015:
Q85
Q.Can multiple 30A rated slip ring legs be combined and connected to a 40A protected circuit? This
configuration was recommended by slip ring supplier.
A.Yes, a parallel connection of two (2) 30A elements would be considered appropriately gauged/rated for
a 40A breaker.
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Unread 08-06-2017, 07:20 PM
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Re: Slip Rings

You'll be surprised what you can find on eBay and Amazon.

EDIT:

Seriously, do some searching on those websites. It's not hard. I know multiple teams who have used Slip-Rings off both of these sites to success. If you really do have trouble finding something, send me a PM or an email to 125( nutrons at gmail )
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Unread 08-06-2017, 09:05 PM
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Re: Slip Rings

Quote:
Originally Posted by kbrowncny View Post
Looking for 12 awg slip rings suited for FRC. Also, posts from teams who have successfully created them on their own as a custom circuit.

Thanks!
2451 PWNAGE Custom Slip Ring from 2012 Offseason

Actually built and tested. Utilized the brush assembly from CIM motors.

2451 PWNAGE Custom Slip Ring V2 from 2014 Offseason

Designed, not built; iteration of previous version. Utilized the brush assembly from BAG motors; included integrated encoder mount.


*Please note that these custom slip rings are not legal for use in FRC. N custom electrical circuits are currently allowed under the currnet rule.
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Unread 08-06-2017, 09:41 PM
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Re: Slip Rings

Team 971 had one on their robot this year and they found it on amazon. They're definitely out there!
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Unread 08-06-2017, 10:04 PM
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Re: Slip Rings

Quote:
Originally Posted by ngreen View Post
I've seen these come up for this question before, but don't have experience with them: http://mwands.com/store/180-amp-6-wire-slip-ring
We used this slip ring on our robot shooter iteration number 3 of 5. Worked great.
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Unread 08-07-2017, 04:50 PM
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Re: Slip Rings

We used this one (purchased from Amazon) on a 30A breaker with a 775Pro.

Great solution for us this year.

//No complaints on the product, but do keep in mind wire routing space/bend radius. These wires were pretty stiff for being stranded. That being said, our 'rotor' wires did a near 90 bend out of the top of the ring with no issues.
//971 may be able to speak more to wire durability as I believe theirs was mounted slightly off the center of rotation which caused wire flex with each revolution.
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Last edited by henryBsick : 08-07-2017 at 05:07 PM.
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Unread 08-07-2017, 05:09 PM
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Re: Slip Rings

Now, I may be wrong in this, but doesn't the slip ring need to be rated for the stall current of the motor, not just the current at the breaker? Sure, you've got the breaker, but you can exceed that amperage at times before the breaker kicks in. Am I wrong here?
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Unread 08-07-2017, 05:21 PM
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Re: Slip Rings

Quote:
Originally Posted by Jjmase123 View Post
Now, I may be wrong in this, but doesn't the slip ring need to be rated for the stall current of the motor, not just the current at the breaker? Sure, you've got the breaker, but you can exceed that amperage at times before the breaker kicks in. Am I wrong here?
The pertinent rule here is R58.
Quote:
Originally Posted by 2017 FRC Game Manual
R58. Branch circuits may include intermediate elements such as COTS connectors, splices, COTS flexible/rolling/sliding contacts, and COTS slip rings, as long as the entire electrical pathway is via appropriately gauged/rated elements
(Emphasis mine)

If you look at Table 8-4 connected to R57 right above, you can see that minimum wire size is based off the breaker size, not the max current of whatever the wire is connected to. Therefore it would be a reasonable assumption that "appropriately rated" in R58 refers to the breaker size as well. That's also how I've always heard it ruled.
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Unread 08-07-2017, 05:46 PM
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Re: Slip Rings

Quote:
Originally Posted by Jjmase123 View Post
Now, I may be wrong in this, but doesn't the slip ring need to be rated for the stall current of the motor, not just the current at the breaker? Sure, you've got the breaker, but you can exceed that amperage at times before the breaker kicks in. Am I wrong here?
Technically, 12 gauge wire (used for 40A circuits on FRC robots) is rated for 34A for solid core, and less for stranded according to this site. The key thing to note is that this is a continuous current rating. This is the same with the 40A (and 120A main) breakers. Their rating is for continuous current, which can be exceeded in short bursts. Otherwise stalling a 4-CIM drivetrain would instantly trip the main breaker at 4x133A >> 120A. FRC is by no means continuous, as robots are only under full load for under 3 min at a time. I would think that it's a similar deal with the slip rings. The rating is for continuous, which can be exceeded in short bursts.
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Unread 08-07-2017, 05:54 PM
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Re: Slip Rings

Quote:
Originally Posted by henryBsick View Post
We used this one (purchased from Amazon) on a 30A breaker with a 775Pro.


//971 may be able to speak more to wire durability as I believe theirs was mounted slightly off the center of rotation which caused wire flex with each revolution.
Can confirm, did try mounting off axis, don't do it, we had some wires fatigue quicker than expected and updated the design to be properly on center.

-Aren
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