pic: 2451 PWNAGE Off-season 2012

[pwnageNick]

What is the shaft made out of? What about the contact rings?

The shaft is made out of G10-Garolite which is an insulator, and the contact rings are made out of Alloy 932 Bronze.

After looking at the picture for a while, I understand why you would want to use two brush assemblies, but the color coding on your wires is a bit misleading, no?

We agree that for it to be competition legal, we would have to change the coloring on the wire.

Seems like a lot of weight and space allocation for an electrical connection.

The module only weighs .75lbs and is L 3, W 4.5, H 5.

If you do run this as part of a swerve, would the two radial bearings on the top and bottom of the shaft take the weight of the robot, or does this assembly go on top of other bearings that supported the robot?

It would be mounted on a structural piece of frame and the shaft would be connected to the swerve module by a flexible hose.

-Nick

[Al Skierkiewicz]

Nick,
I have to say this is an amazing assembly. Nice job to everyone involved. Unfortunately, the COTS rule (quoted above) on slip rings seems to take precedent. If team built slip ring assemblies were to be considered, this design surely would be on the top of my list as an allowed item! I like the dual brush assembly design. I doubt that you would experience any wear or deterioration with the use of just one brush per ring either. The CIM brush assembly wears mostly due to the commutator edges and arcing. Neither would be present in this design. Did you design the ring to be the same diameter as the CIM commutator or did you contour the brush to match the ring? Maximum brush contact with the ring is essential to keep resistance and heat to a minimum.
I see nothing that would flag this as contrary to electrical practice, it seems as if the team has thought of everything. Prior to the rule on COTS slip rings, I would have allowed this in and FRC robot.
Did you have to sacrifice CIM motors or were you able to find the brush assemblies as separate items? I would bet that further refinements could bring the cost and weight down as well. In this service, ball bearings are not needed unless you are using the bearing for other purposes. The rotational speed is low and the range of motion over it's lifetime is also very low. The brushes would naturally follow any runout in a simple sleeve bearing. I like the addition of the rotary encoder as well.
All in all a very well thought out design. Congratulations!

[jspatz1]

In 2010 (prior to the current rule allowing COTS slip rings, and in the only year we had occasion to test the issue) slip rings were not mentioned in the rules, and any type of slip ring including COTS or home-made were disallowed by the Q&A forum. Prior to that they had been allowed by the Q&A Forum on several occasions, even though they were likewise not mentioned in the rules. Now that it is specified in the rules that they are allowed but must be COTS, it would seem that the issue is pretty clear cut, however there has been unpredictability on this issue with the Q&A Forum.

[Gregor]

Ignoring R 44, wouldn't R 49 come into place?

[R49]
Motors, servos, and electric solenoids used on the Robot shall not be modified in any way, except as follows:
A. The mounting brackets and/or output shaft/interface may be modified to facilitate the physical connection of the
motor to the Robot and actuated part.
B. The electrical input leads may be trimmed to length as necessary.
C. The locking pins on the window motors (PN 262100-3030 and 262100-3040) may be removed.
D. The connector housings on the window motors (PN 262100-3030 and 262100-3040) may be modified to
facilitate lead connections.

Modifying the CIM would be disallowed, and we can bet this rule is here to stay.

Regardless, nice engineering exercise.

[Chris is me]

Originally Posted by Gregor

Modifying the CIM would be disallowed, and we can bet this rule is here to stay.

The rule concerns modifying motors used on the robot. While these parts come from a CIM, they are certainly not being used as a motor on the robot.