- Location
- Bloomington, Indiana
Some weeks ago we did a training session that consisted of lift tests using various friction devices. A dynamometer (courtesy of Harvey Holt and Purdue University) was attached to the base of a tree with a sling. A block was installed in a crotch using a static retrievable false crotch (the topic of a previous training session) with a 1/2 double braid reeved through the block. The working end of the rope was tied to the dynamometer and the standing part was wrapped on various friction devices and then tensioned by a volunteer.
Two volunteers each tried to generate as much force as possible on the dyno. One of them weighs about 150 pounds, the other weighs about 220 pounds. The volunteers first just pulled on the line, then were allowed to pull, lean on or jump on the handle of the friction device to achieve a maximum force on the dyno.
The friction devices that we used were a 2003 Lowering Device (sometimes called a Hobbs); a 2005 (modified) Lowering Device; and a Good Rigging Control System (GRCS). The handle of the GRCS will lift when turned in either a clockwise or a counterclockwise direction and both directions were tested.
The strongest lift was generated by the GRCS turned in a counterclockwise direction. This was followed by the GRCS in a clockwise direction, the LD 2005 and the LD 2003. A speadsheet is attached.
We also tested the pull achieved with a 5:1 mechanical advantage (MA) system. We did this because our crews sometimes use a 5:1 (set up horizontally) to gain MA while using a port-a-wrap and I wanted them to actuallly see how the systems compare. Sorry I don't have a spread sheet for the 5:1, but it generated sometimes more, sometimes less than five times the weight of the volunteer.
Mahk
Two volunteers each tried to generate as much force as possible on the dyno. One of them weighs about 150 pounds, the other weighs about 220 pounds. The volunteers first just pulled on the line, then were allowed to pull, lean on or jump on the handle of the friction device to achieve a maximum force on the dyno.
The friction devices that we used were a 2003 Lowering Device (sometimes called a Hobbs); a 2005 (modified) Lowering Device; and a Good Rigging Control System (GRCS). The handle of the GRCS will lift when turned in either a clockwise or a counterclockwise direction and both directions were tested.
The strongest lift was generated by the GRCS turned in a counterclockwise direction. This was followed by the GRCS in a clockwise direction, the LD 2005 and the LD 2003. A speadsheet is attached.
We also tested the pull achieved with a 5:1 mechanical advantage (MA) system. We did this because our crews sometimes use a 5:1 (set up horizontally) to gain MA while using a port-a-wrap and I wanted them to actuallly see how the systems compare. Sorry I don't have a spread sheet for the 5:1, but it generated sometimes more, sometimes less than five times the weight of the volunteer.
Mahk
