Continuous turret

[kmcclary]

Originally Posted by Ian Mackenzie

As much as I'd like to use slip rings (commercial or otherwise) one year - they could be very handy for swerve drives - I'd be a bit worried:
(
...badly paraphrasing the rules here, for brevity... -Keith
- <R58> (all wiring must be isolated from the frame...)
- <R85> (must use copper wire for all wiring - no aluminum, etc...)
)

I think you could argue that a commutator involves using the robot frame to carry electrical current, illegal according to <R58>; unfortunately, 'frame' isn't defined. Even if you argue that the commutator isn't part of the actual robot frame, but a separate, isolated piece, I certainly think a commutator is an example of an electrical connection using something other than copper wire, in contravention of <R85>.

BTW... OOC, before I forget, how much is the Mercotac unit, anyway? Their 830 (8-conductor unit) is definitely cool. You could tie several 30A motors to it, with data lines to spare, but I didn't see prices on their site. (I worry whenever a site makes you RFQ an item. That normally means it's outrageously EXPENSIVE!)

Anyway... First off, to answer one question "Frame" is commonly defined as the metallic chassis of the robot, the cases of the motors, etc. They don't want the chassis used as a power ground return, for a number of safety related reasons ("floating ground wiring" only). This IS a good rule.

(<R58>) - IMHO R58 isn't a problem here at all. As long as you don't use the frame itself for ANY of the connections, it doesn't apply. (IOW, simply add another ring!)

(<R85>) This however, is a different story...

But remember - A slip ring is a CONNECTOR, not a "wire", and you ARE allowed to use "connectors" to your heart's content! Therefore, *I* would argue that as long as it's either a COTS slip ring assembly, made completely from COTS items (copper pipe, PVC, graphite brushes, etc...), or SCAVENGED from a COTS item (e.g. take the ring set out of an old alternator), AND it is sized to handle the current needed, AND it's insulated properly, it therefore isn't a "wire", and R85 doesn't apply.

But, IANAFRL (I am not a FIRST Rules Lawyer)... so I definitely think once you have decided on a way you want to do the slip rings, a Q&A question posing it is in order to get a final ruling on the subject.



Other slip ring ideas to explore (and/or comment on):

A "hardware store" homebrew version may be simply made using a pair of nested PVC pipes, separated by flanged bearings on the ends. Slice up some rings from the next size larger copper pipe for wrapping around the inner PVC tubing. The outer pipe has a series of "T" connectors along it to hold motor brushes (an opposing pair for each ring, connected together). Now use hardware store replacement spring loaded graphite motor brushes within the "side lobes" to contact the copper rings, and screws on their endcaps to give you a connection point. You'll need a grooved or X-shaped stick glued into the middle to hold the center still, yet allow wiring into the core. (I've seen this on the net before, but I couldn't find a good photo for it. Sorry...)

Yea, that's a lot of fab at this stage of the game, but it's all hardware store items!

For those interested, here are a few more links for homebrewed & COTS slip rings:

1) A COPPER version of the above homebrew slip ring set:
http://www.maybevideodoes.de/howto/o...ing/index.html

2) United Equipment Accessories (no clue on price & availability)
http://www.uea-inc.com/slip/small_bore.html

3) Michigan Scientific Corp (again, no clue on price & availability)
http://www.michsci.com/Products/sliprings/slip.htm

4) ...and lastly, Global Spec search engine results (52 slip ring manufacturers found - but you must register to use the engine's output)
http://motion-controls.globalspec.co...ols/Slip_Rings

I hope this helps!

- Keith