D1 Version A |
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D1 Version B |
D1DB |
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D1a |
D2,
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D2,
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D2DB |
RS1a |
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RS2a |
DS1 |
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RS6DBs |
The 2000 Single Rope Technique Equipment catalog listed 20 different versions of their stop bobbin, and if you include double brake attachments on the rescue stops (RS models), the total would be 32. Adding older and newer designs would greatly increase the number of variations. I don't expect to collect them all, but I can show a fair cross-section of the previous and current models here.
[ Top | D1 version B | D1DB | D1a | DS1 | D2 Version A | D2 Version B | D2DB | RS1a | RS2a | RS6DBs | Return to Bobbins ]
I acquired this D1 used from Tom Vines in 2006, but it dates from the 1980s.
The main differences between this one and D1 Version B are the tubular plastic handgrip (also seen on D2 Version B), and the details of the handle casting, particularly around the upper bollard. The rope groove on Version A has more of a V-shape than the U-shaped groove on Version B, and the eye on Version A is smaller and more rounded than the D-shaped eye on Version B.
[ Top | D1 version A | D1DB | D1a | DS1 | D2 Version A | D2 Version B | D2DB | RS1a | RS2a | RS6DBs | Return to Bobbins ]
I acquired this descender from Inner Mountain at OTR in 1988.
The SRT differs from other bobbins in that both bollards and the autostop handle are part of a single ferrous casting. This casting is mounted between a fixed and a pivoting side plate. The side plates are 3.3 mm. red anodized aluminum. The attachment points are essentially the same as those on the quick attach bobbins, and feature a similar guard on the pivoting side plate. The side plates extend outwards (opposite the handle side) at the top, and a 16 mm. cylinder is bolted to the fixed side plate. A notch in the pivoting side plate mates with a notch in this cylinder when the side plate is closed. The bollard casting pivots about a nut passing through the lower bollard. On rappel the bollard casting tends to pivot and force the upper bollard towards the anvil, squeezing the rope and ideally arresting the descent. The required torque is provided by the friction generated by the ropes passage augmented by the asymmetrical loading resulting from the "S" curve in the rope. A hole at the top of each side plate is aligned with a hole in the upper bollard, and allows insertion of a carabiner to prevent this rotation and deactivate the autostop feature.
The pivot deserves some special discussion. Rather than simply drill a pivot hole in the lower bollard, SRT casts a hexagonal cavity into the bollard. A hexagonal aluminum bushing with an off center hole can be placed into this cavity in six different ways, thus moving the fulcrum with respect to the handle. A spring is also provided to hold the handle open during storage, and functions in the same manner as on the Petzl Stop.
The pivoting side plate is stamped with an icon illustrating how the descender is threaded, but anyone who needs this assistance shouldn't be using a bobbin anyhow. It is also stamped "PAT. PEND", "MAX. 800 Kg", "ROGELJA", and "AUSTRALIA". The pivot bolt head is marked "IVS" and "A2". The anvil bolt head is marked "A2-70".
The descender seems to provide about the same amount of friction as most bobbins, so is fast for my taste. The good news is the autostop feature holds securely. The bad news is that it takes quite a bit of effort to hold the handle to keep the autostop disengaged. The reason is that squeezing the handle causes rotation which lifts the upper bollard, and the trailing rope with it. In fact, if one stops then uses the other hand to apply a strong hip brake, squeezing the handle actually lifts the rappeller upwards. The result is that one's handle hand becomes tired very quickly.
I tried varying the friction by rotating the internal hex bushing as indicated in the instructions. It is a fairly easy task to make the switch, but I could notice no differences on rappel. Despite the documentation, I doubt that the hex bushing affects friction much at all, since the relative location of the two bollards is fixed, and that should control the friction. I was hoping that the force required to hold the handle down would vary, since the fulcrum is being moved, but in all cases the force required was so high that I could not notice any change. If I were redesigning this bobbin I would consider moving the third anvil up and closer to the other two, possibly sacrificing some holding power for ease of use.
The bollards themselves are ferrous rather than aluminum, so they should be expected to heat more. I noticed this in qualitative testing, but have not had the opportunity to quantify the difference.
The basic SRT Stop Bobbin is protected by U.S. Patent #4,596,314, but the more modern design (specifically the D1a) shows up in U.S. Patent #5,954,153. Boris Rogelja holds these patents, which explains the stamping on the side plate. There are several other interesting patents, but I'm saving them until I get the specific versions of these bobbins to test.
In general this bobbin is very well made, and the autostop
functions well, but it is very tiring to use.
[ Top | D1 version A | D1 Version B | D1a | DS1 | D2 Version A | D2 Version B | D2DB | RS1a | RS2a | RS6DBs | Return to Bobbins ]
I acquired this D1DB from Single Rope Technique in 1989.
This is a newer version of the D1 with a double-brake attachment added. The basic descender has eliminated the carabiner hole seen on the D1 and replaced it with an 8 mm. hole for a pin. Inserting the pin overrides the autostop feature. Unfortunately, the pin hole was only drilled in the fixed side plate. This is an obvious oversight in manufacturing that does not reflect well on the manufacturer's quality control at the time.
The double-brake feature adds a brake shoe so that over-squeezing the handle, such as a person might irrationally do while panicking, adds friction in an attempt to stop the rappeller. Naturally, there will not be enough friction if the rappeller is not panicked enough. The double-brake feature adds considerable weight to the basic device. It can be defeated by rotating the shoe out of the way, but only if the descender has been adjusted to the lowest setting of the hexagonal insert. It can also be removed, although one might need to find shorter bolts if they choose to do so.
[ Top | D1 version A | D1 Version B | D1DB | DS1 | D2 Version A | D2 Version B | D2DB | RS1a | RS2a | RS6DBs | Return to Bobbins ]
I acquired this D1a from Inner Mountain Outfitters in 1996.
This is another version of the D1, with a different side plate design and an additional cylinder bolted inside the frame. Under the new numbering scheme, the "a" in D1a means aluminum side plates. This is one of the current production models. This is the design shown in in U.S. Patent #5,954,153.
[ Top | D1 version A | D1 Version B | D1DB | D1a | D2 Version A | D2 Version B | D2DB | RS1a | RS2a | RS6DBs | Return to Bobbins ]
I acquired my DS1 used from Richard Wolle in 2007.
This version is similar to the D1a except that it has stainless steel side plates. This is the only STRE in my collection that does not have a handle cover, but one could have been removed by the previous owner.
[ Top | D1 version A | D1 Version B | D1DB | D1a | DS1 | D2 Version B | D2DB | RS1a | RS2a | RS6DBs | Return to Bobbins ]
I acquired this D2 from Raven Products in 1990.
This version is for double rope. It represents an early design. Not only is the handle different, but the handle assembly differs from the one inD2 Version B, particularly in the area of the top bollard.
[ Top | D1 version A | D1 Version B | D1DB | D1a | DS1 | D2 Version A | D2DB | RS1a | RS2a | RS6DBs | Return to Bobbins ]
I acquired this D2 from Single Rope Technique in 1989.
This is a later version is double rope. It was subsequently replaced by the current model, which has a frame similar to the D1a. Note the disarming pin that keeps the stop feature from activating. The disarming pin does not have a spring-loaded ball, so it tends to fall out if one isn't careful. The older Version A had a carabiner hole that served the same purpose.
[ Top | D1 version A | D1 Version B | D1DB | D1a | DS1 | D2 Version A | D2 Version B | RS1a | RS2a | RS6DBs | Return to Bobbins ]
I acquired this D2DB from John E. Weinel, Inc. in 1989.
This double-rope version has a double-brake attachment added.
[ Top | D1 Version A | D1 Version B | D1DB | D1a | DS1 | D2 Version A | D2 Version B | D2DB | DS1 | RS2a | RS6DBs | Return to Bobbins ]
I acquired this RS1a from Single Rope Technique in 2000.
The RS1a is an aluminum-frame rescue stop bobbin designed for 9 to 13 mm. rope. The friction post is free-swinging. It has two notches that the rope can be fed through. Not only does this provide friction on the trailing end of the rope, but it also squeezes the rope between the friction post and the bollards.
The friction post design is protected by U.S. Patent #5,597,052.
[ Top | D1
Version A | D1 Version B
| D1DB | D1a
| DS1 | D2
Version A | D2 Version B
| D2DB | RS1a
| RS6DBs | Return
to Bobbins ]
I acquired this RS2a from Single Rope Technique in 2000.
The RS2a is similar to the RS1a, except that the friction post
is cut short and only one notch is available. This means that
less friction is available, so Single Rope Technique specifies
a rope range of 11 to 13 mm. for this descender.
[ Top | D1
Version A | D1 Version B
| D1DB | D1a
| DS1 | D2
Version A | D2 Version B
| D2DB | RS1a
| RS2a | Return
to Bobbins ]
I acquired this RS6DBs from Single Rope Technique in 2000.
This is a double-rope version designed for 16 mm.
rope. The frame is stainless steel (all current Single Rope Technique
bobbins come in both aluminum and stainless steel versions). I
had a double-brake attachment added to this one. The lower bollard
rotates, much like a pulley, which helps reduce the friction normally
encountered with the oversize ropes used by the "bigger is better" crowd. There are two
subsidiary bollards for those who want to increase the friction.
For some reason, the hole for the disarming pin does not line
up with the hole in the upper bollard, so the pin cannot be used.
[ Top | D1 Version A | D1 Version B | D1DB | D1a | DS1 | D2 Version A | D2 Version B | D2DB | RS1a | RS2a | RS6DBs ]
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©2008, Gary D. Storrick
