Hello CD!
I’m the programming and electrical lead for team 4388 and we are wanting to create a turret for our robot and we hope to make it turn more than 360 degrees. I have done some research on slip rings that can carry enough current and 8 conductors for motors and signal but have had no luck finding any that aren’t very expensive, around the $600 range. If anybody knows any good slip rings I’m open to options and alternative methods.
Thanks!
It is week 4. A turret is a very complex design element. By the time you get the parts needed to make it, it will be week 5 or 6 and you will probably not finish. Sorry to be so blunt but I’ve been in that position with an unfinished robot and do not want to see anyone else in they position.
We used these last season:
Not quite what you wanted, but close.
a) Turrets are complicated, do you REALLY need it.
b) Turrets without slip rings are fairly common. You just have to have extra wire to wrap. You won’t have infinite travel but you can do more than 360.
c) Slip rings with those criteria ARE expensive. I’ve got some that can handle one motor that’s pretty cheap. Much past that… yeah nope.
Schedule aside, please reread R9 (specifically H. in the blue box) and R11.
Many slip rings contain mercury.
Six wires should be enough for two motors with feedback, if you can get enough power through two 30A breakers. Put two Talon SRXs on the turret. Run power for them and one CAN pair. Terminate the CAN bus on the turret so you don’t need it to return. Then wire sensors to the SRX inputs. You have four limit switches and at least two encoders or analog sensors you can connect, getting all that info back and forth through two wires.
Are you certain that the implementation of CAN used on the RoboRIO will operate in a noisy environment like that? I know that some implementations are capable of that but I don’t know the details behind ours (or those implementations). From what I understood the more noise you deal with the less speed the bus operates with.
Personally, I would question the requirement for unlimited rotation. You don’t need something that can do absolutely everything in every situation. If you can reduce complexity by building to just 90% of anticipated situations, then I’d do that and give yourself more time for debugging and driver practice.
I would agree with Jon. In 2012, my team (at the time) had far more range than we ever used on the turret. The fact is, you can rotate your robot with its drive train to get close to where you want to aim, then use a finer grained adjustment on a turret to do final alignment. Will save a lot of time and your drivers will do this anyway, even if you have >360 deg rotation on the turret. So a lazy susan with a cable tether is likely the right solution here, IMO.
Thanks for the feedback. Thinking about it now it does seem overkill but it still might be something good to test in the future to see if the CAN bus would work with that much noise along with the amount of current needed to run motors.
Sauce,
You can redesign the position of your controllers so that you don’t have to pass CAN through the turret. this should reduce your wire needs. You can also parallel lower current contacts to increase the amount of current you can pass to the turret.
I agree with others, that for this game, continuous 360 degree freedom is not needed. You can easily get 500 degrees of rotation without the need for a slip ring design.
Only because you asked. The Mercotac models are small and versatile. But I too think this (revolving turret) might be overkill for this game.
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Mercotac received that name because they contain mercury. They are not legal for FRC robots.
Thank you Al, your of course correct. I had overlooked that aspect, but as an inspector you of course hadn’t. Had just used one in a work application and had it come to mind when I read the question.
This is not to say that Mercotac parts are bad and are in fact used in a variety of applications. I talked to an application engineer at Mercotac and he told me that if temperature or current specs are exceeded, mercury could exit the part, albeit in very small quantities. This is one of those parts that is listed as “mercury wetted” as opposed to “mercury filled” contacts.
I agree with the others this seems excessive.
Am curious if one is allowed to manufacture a slip ring using concentric circles of exposed solid copper wire pressed into a non-conductive plate and copper shoes on the opposing plate with a Lazy-Susan bearing as the pivot. I have actually done this before outside of FRC for contraptions but what about on a competition field?
R50 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.
Here is a $16 possibility, 24 rings, parallel some for higher currents
Az:
http://www.goldmine-elec-products.com/prodinfo.asp?number=G20822
Rare and unique Senring SNMO12A-24-1 24 conductor slipring made for data, video, rotating stage lights. Consists of a fixed component and a rotating component for conducting signals and power to a rotating item (360 degrees). This model is for up to 24 wires and is rated for up to 250 RPM. Rated for 2AMP maximum per ring. Maximum voltage is 210VDC or 240VAC. Size 15.5mm dia. X 39mm (L). These are extensively used in CCTV pan/tilt camera mounts, electrical test equipment, stage lights robotics and medical equipment.