Professional Portfolio
Pull Assist (Greenlee)
About the Pull Assist
The Greenlee Pull Assist is an accessory which removes the physical effort from pulling cables through conduit. The operator is still in control of the pull, but the Pull Assist does the heavy lifting. This product is now available for sale, and was on display at NECA 2021.
So, what is the physical effort that the Pull Assist does for you? Well, we first need to understand how cables are pulled through conduit.
First, a length of rope is "fished" all the way through the empty conduit run. The cables are then attached to the
end of the rope, and then the cables are pulled back through the conduit using the rope.
Pulling cables this way can require pulling forces of up to 10,000 lbs, so most pulls are not done by hand. Instead, a machine, simply called a, "cable puller", is used to pull the rope. Most cable pullers do this using a motorized capstan. A capstan is a rotating cylinder, around which the rope is wrapped several times, which generates enough friction between the rope and capstan to pull the rope as the capstan rotates.
However, in order to apply and maintain the friction between the rope and the capstan, the other end of the rope (the "tail") must be held with some force ("tailing force"). Typically, this tailing force is applied by hand, with the operator standing next to the puller, and physically pulling the tail of the rope as the capstan rotates and pulls rope along. Manually applying this tailing force cause repetitive stress injuries, and lead to slow pulling as operators tire.
That's where the Pull Assist comes in: the Pull Assist is capable
of grabbing and pulling the tail of the rope, completely
removing the need for any physical labor, while still allowing
the operator to adjust the tailing force as needed by way of
the handhenld pendant controller.
This product is composed of a self-contained drivetrain,
a power supply board and a control board, a sheet metal
enclosure and frame, and a cast aluminum V-pulley to grab
the rope. The sheet metal enclosure houses both the drivetrain
and the electronics, which required in-depth collaboration
between the mechanical team (mostly myself) and the
electrical team.
The drivetrain consists of a brushless DC motor, a 6:1 planetary
The drivetrain consists of a brushless DC motor, a 6:1 planetary
gearbox, and a 60:1 worm gearbox. This drivetrain was chosen
to maximize power while minimizing size and weight. This was
a project in and of itself: in theory, so long as the motor can
deliver the required horsepower, you could get a very slow
motor that directly outputs the required torque and speed.
However, such motors are typically larger than a football,
and weigh many tens of pounds by themselves. Conversely,
you could get a very small, very fast motor, with very little
torque, and then gear it way down. However, this would
require a massive gear reduction, which quickly becomes
large and heavy.
Between these two extremes is a minimum of size and weight for the drivetrain, and it was the aforementioned gearing system, combined with a motor only slightly larger than a film canister, which allowed us to achieve our weight target, with the Pull Assist weighing just 22 lbs in total.
