Unicender

Front View

Side View

Technical Details

Morgan Thompson donated this Unicender in 2005.

The Unicender is made from six pieces of milled 6061-T6 aluminum connected by steel links. Each link looks like a bicycle chain link with a 15.5 mm pitch and 5 mm pins between the two sides. Stainless steel clips on one side engage grooves in the cross pins, holding the device together. There are six aluminum blocks Each block is 32 mm wide and 12.7 mm thick unless otherwise noted. From top to bottom, they are as follows:

1. The top plate is 35.8 mm long. It has a 16 mm hole with edges beveled/rounded on both sides. This provides a tie-in point for double rope technique.
2. This plate is 75.5 mm long. There is a 13 mm wide slot cut in the right side about 21 mm from the connecting pin axis. This slot slopes at 45° downward to the front (away from the pin). The outer 27 mm is reduced to 7.5 mm thickness, and widens to 44.5 mm. This provides a control tab (a.k.a. upper handle).
3. This plate is 50.7 mm long. It has a slot like the second plate, except the slot opens to the left.
4. This plate is a mirror image of the one above: the slot opens right.
5. This plate is similar to the third plate except that the outer 27 mm taper in thickness to 8.5 mm. This plate is also spring-loaded upward; none of the other plates have springs.
6. The bottom "plate" is actually an L-shaped bracket. Each arm is 12.7 mm thick.
   1. The horizontal arm (a.k.a. lower handle)is 77 mm long and ends in side ears giving a total width of 64 mm. The a 14 mm central slot is cut the length of the arm and beveled on the top and bottom.
   2. The vertical arm is 76.2 mm high and features a 52 by 16 mm beveled slot. This is the main tie-in point.

There are no markings on the Unicender.

The manufacturer provides the following test data:

• Breaking strength: 7000 lb (3200 kg; 31 kN)
• Slippage on 1/2" (12.7 mm) rope: 1600 lb. (720 kg; 7.1 kN)
• Slippage on 7/16" (11 mm) rope: 1000 lb. (450 kg; 4.4 kN)

Comments

The Unicender is a very different ascender than the others on my site. Morgan Thompson designed it for arborists, not cavers and climbers, and it seems unfair for me to evaluate it as a caving device. I've received a few emails from arborists impressed with the device, saying it works very well for both single and double rope technique. One claims that for SRT, it works very well as a descender but needs some work as an ascender. He put it in the 95th percentile. I'm not Tarzan (I'm an underworld character instead) but I can understand and credit these opinions.

When descending, one can control speed by squeezing the top and bottom handles together. Looping the rope over the lower handle provides additional friction. The aluminum blocks provide good heat dissipation.

The clips holding the links together look scary, but they are not loaded and they are more secure than they look

I doubt that the Unicender would make a good caving ascender, but it was never designed as one. I would be curious to see how it fares in heavy mud: I think I might be rather surprised. The manufacturer warns against using it on icy ropes.

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©2007, Gary D. Storrick