Overrunning Clutch Application in FRC

[lewislongbottom]

I was wondering if anyone here has used Overrunning Clutches on their robot mechanisms? I’ve seen very limited discission over them on CD so there may be a good reason for that. My inital thoughts were installing one on the drive of a flywheel, but I’m wondering if others have any ideas and associated pros and cons. They might be a fairly complex mechanism to design and definitely not, off-the-shelf, but that doesnt mean they couldn’t be in the future for smaller FRC applications. Any thoughts would be appreciated.

Here’s a link to a video explaining them, from the experts at SSS Clutch.

SSS Clutch Hand Model - Overrunning Clutch design

[Skyehawk]

Not that I know of, (although I’m sure someone has)

I think this is because we have a lot of motors in FRC, it is easier to link something to its own motor, vs a pto.

I can’t really think of a situation where massive over speed happens in FRC that this may be useful practically.

Now in more out of the box ideas (store energy in a flywheel for later engagement) this could have a place.

[nuclearnerd]

I believe 118 used a one way clutch in other to drive their climbing winch from both sides of their drive train:

The Robonauts 118 - 2017 Video

Bold added. ASmith1675, you and I have wildly different views of “fairly simple” I guess. Whenever our team considers a robot feature, I mentally start to add up the number of shafts/axles. When I get to 10, I am pretty sure that amount of complexity ain’t gunna buy its way onboard the final robot. Not that we can’t have complicated things. It is just that for most teams I’ve been involved with, that amount of complexity is something that you have to approach with your eyes wide open, knowin…

[Skyehawk]

Iirc that was a ratchet and pawl situation, but the point does stand, they are used.

I think CD has mostly focused around sprag clutches in discussion (or ratchets) without a whole lot of thought to other clutch designs.

[lewislongbottom]

Yeah, its a very niche application unfortunately. Very neat in that theres no electrical and programming involved, and very reliable when built right.

[Mark_Wasserman]

Soooo… this is a one way clutch?

Otherwise known as a sprag clutch.

[lewislongbottom]

I believe so because rotating the driven input in reverse would disengage the driven end. Since its a ratchet and pall mechanism, I dont think its possible for bi-directional. Maybe this exists for higher loading applications which is where I’ve seen it in O&G.

[asid61]

I think I made one of these by accident a long time ago in a swerve drive:

The in-wheel swerve shifter!

So I made an autoshifter in CAD using a weird custom dog, parts from the GEM gearbox (ring gear is a measely $10 vs. $100 for other internal gears) modified for this purpose, and a custom wheel made to fit the ring gear. The way this works: There is a primary reduction from CIM to wheel shaft. The shaft is spinning in one direction, say, clockwise. The dog is keyed to the drive shaft and spins with the shaft. It also engages with the hub of the wheel, to direct drive the wheel from the sh…

I would probably use a one way bearing sooner than this, due to the low torques we work with.

[IKE]

There are several different and interesting designs of “one way clutches” or “mechanical diodes” as some refer tot hem. Sprag is one. 1-Way roller bearings is another very similar, but slightly different. The Sprag and “roller bearing” style often work off of directional wedge of the rolling elements. Ratchet and pawl is another type.

This design is pretty neat as it effectively is engaging a small section of a spline type section which should lead to a very high capacity potential. Pretty clever.

Ratchet and Pawl get used a fair amount in FRC. Especially for climbers. Many of the rope climbers in 2017 quite literally used a ratchet wrench connected to the 1/2" hex shaft as a way to make an “anti-back drive” mechanism. 2337 used ratchet and pawl on the “shoulder” joint of a large arm in 2011. It wasn’t to permanently hold the arm in one place, but instead was engaged to friction element when the arm would move in the downward direction. This kept the arm from crashing down when being lowered, but didn’t add friction when the arm was being raised. It was a clever idea, though most teams would instead utilize some sort of bungee/spring/gas shock arrangement to do a one directional drive enhancement.

[troy_dietz]

Iirc 254 used a one way bearing in a functionally equivalent way to allow their shooter and climber to share motors. Not sure if it was 2017 or a later year.