Staring at Stairs, Part 2

After fussing with the finicky clutch mechanism on a Zebco casting reel for about an hour, I decided to take a second look at a winch based approach.

My next iteration was a type of winch called a lashing winch. This type of winch is typically placed along the perimeter of flat bed trucks and is used to tighten 2 inch straps.  Please see the Figure below.

Lashing Winch

Lashing Winch

The threaded rod is about 2 Feet in length and installs into the winch by the crossdrilled set of holes.  My hope was that the lever length would provide Dave the minimal effort required to comfortably rotate the winch.

Please see a first pass test of lashing winch below.  Simulated grocery mass is a 40 pound bag of water softener salt. 

 

Testing revealed two issues with the lashing winch concept.  Both issues relate to the clutch release mechanism. This is the gold colored feature in the top right corner of the winch.

The first issue is that the latch  permits the load to freewheel downward. In other words, if the weight of groceries is not removed prior to releasing the clutch two things happen very quickly.  First, the cart returns  to the bottom of the ramp.  Broken eggs anyone?

Second, the rod separates from the winch by centripetal acceleration.  Depending on where the rod is positioned when the clutch is released, the rod becomes a projectile.  Again, not cool.

Human Factors 101

I can not guarantee that Dave will follow the safe procedure of:

1. Wind winch

2. Remove groceries

3. Release latch

Only 3 steps right? There's an interesting book that I read recently called "The Checklist Manifesto" by Atul Gawande.  Doctor Gawande is a surgeon. who presents the idea that virtually all processes, no matter how simple, can benefit from the use of a checklist.

In the book, Dr. Gawande describes a study performed by a colleague at Johns Hopkins involving the placing of a central line in a patient. This procedure had only 5 steps which were:

1. Wash hands with soap

2. Clean the patient's skin with antiseptic

3. Put sterile drape over entire patient

4. Wear a mask, sterile hat, gown and gloves

5. Place a dressing over the site 

As a patient, we'd hope that these are common steps any healthcare practitioner would take. But many doctors did not follow procedure.

A checklist was created and nurses were empowered to stop a doctor who did not follow the checklist.  End result? Over the one year study  period, 43 infections, 8 deaths and 2 million dollars in costs were saved. This is for one hospital.

So what does this have to do with engineering? A lot more than we might expect.

Even with a simple 3 step process, I can not ask Dave to use a checklist to lift his groceries.  People are not perfect. We forget things. We get distracted.  I need to find a winch that will hold the load - even if the force is removed. So on to the next style of winch.

The Worm Winch

One of the premier manufacturers of winches is Dutton-Lainson Company, a company that has been producing winches since 1886. More types of winches than this ME has ever seen.  The most intriguing is the worm winch.

Driven by a worm gear, the winch holds loads stable, with and without load.  It also can be driven by a drill, rather than a hand crank.  Perfect for Dave. Please see below.

Worm Winch

Worm Winch

Please see next post for Worm winch testing.