/ Revolver Krab - Pulley Strength Question
1) the pulley stops rotating
2) the pulley becomes irreversebly damaged
I've contacted DMM in parallel but wondered if anyone on here knew?
The pulley stops rotating at around 11.5kN. At this point the Revolver acts as a full strength carabiner - the pulley and its mounting / housing does not compromise the overall integrity of the carabiner.
The pulley bearing can be deformed permanently at forces around 16kN - we have never seen this happen in real life.
Hope that helps
Awesome, thanks Simon
Short of making a rotating housing in the bottom of the crab for the pulley, which would greatly increase the size and therefore the weight of the whole unit, how do you suggest it might be improved whilst retaining the pulley facility? I must say, the revolver is one of my favourite pieces of kit.
i might add I am not a designer/engineer and am not expected to come up with a solution, I just notice the problem, the solution is for DMM to make.
i have 2 of these and like them. but they can be improved.
I'd say that on occasion, the rope doesn't pass directly over the pulley so I can see where you're coming from. This doesn't happen all the time AFAIK, so wouldn't really class it as a design 'flaw'. There will be a reason the pulley is located exactly where it is.
I think we can rest assured that DMM will have tried many profiles before deciding on the current design.
This is an interesting thread from DMM's point of view because there is some truth in gd's observations, but the simplistic nature of his statements warrants a reply.
Can you load the Revolver off centre and in a manner whereby the rope seems to be running off the roller - certainly, but it is worth looking at this a bit more closely.
If you were to mark the roller with a horizontal black line and then try to load the roller so that the rope is pulling off centre you will see roller is still rotating uniformly and if you look at the load point of the rope you will see that this is still (primarily) on the roller - the Revolver is still reducing friction and improving efficiency.
It is simple to demonstrate this - just run a heavy load over a Revolver, get the rope to run off centre and pull the load up - repeat with a normal biner. The result is pretty obvious - the weight is far easier to lift with a Revolver no matter how it is loaded - we have demonstrated this a huge number of times at the various events we attend.
Loading off centre is maximised with thick, old single ropes on Revolvers that are unable to move/rotate; it it is minimised on half ropes and modern singles on Revolvers that are able to move or rotate easily. Perfect - no; pretty damn good - yes - and a lot better that using a standard biner in a pulley/friction reducing system.
I'll get some numbers/video sorted to illustrate this.
The comments regarding design are particularly crass - the Revolver was in the design office/tool room/testing stage for about two and a half years and it's development heralded one of the biggest changes in recreational carabiner design (hot forging + I-beaming carabiner backs) seen in the last decade.
The behaviour characteristics of the Revolver under load are far more complex than a standard carabiner - taking a chunk of metal from the very area that is designed to take most load whilst also drilling an axle hole through the same area presented a lot of design challenges. Plus we had to add a rigid steel axle that totally changed how a carabiner behaves under load whilst adding several interacting moving parts that had to perform consistently over a period of years in a very wide range of conditions.
A key design feature - and core to answering the posters comments - was that we needed to make sure that the rope bearing surfaces - the back, the roller and the back/roller intersection all presented a smooth, safe rope bearing radius in all circumstances. This is key because a steeper bottom on the back bar - the ideal way of forcing the rope onto the pulley - could create possible stepped edge issues.
An awful lot of thought + testing went into the design of the Revolver taking into account all sorts of issues/situations/systems/misuse - the shape and geometry are unique and were not predictable by FEA - just the result of a lot of time, knowledge + prototypes.
Nine years on and there is no competitor to the Revolver - nothing has come close or improved on it and this a large testament to Fred and Gethin's design work.
There are no plans to modify the current series of Revolvers, but there is strong demand for a bigger, industrial version of the Revolver with a larger diameter/more efficient roller that will work with larger diameter ropes and this is on (long) list of things to do.
Cheers for the detailed, explanatory response, thanks Simon.
> This is an interesting thread from DMM's point of view because there is some truth in gd's observations,
Thanks for your reply Simon, and clearing things up it is much appreciated. DMM is an excellent British company, I am always happy to buy/use your gear and have a rack full that I use regularly.
I only know simplistic and crass ;)
> I only know simplistic and crass ;)
I thought that was a it harsh too: surely you have to pretend the customer is always right?!
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