Pop Up Part 1
Pop - Up Mechanism
Here it is... at least the start of it.
This is a front view of the simple pop-up stand,
my version of a home-made PVC air cylinder,
and the upper - body frame for this prop.
This is the "shoulder" part of the prop.It is nothing more than a 3/4" PVC
"cross" with two 6" sections of 3/4" PVC .
I glued a 3/4" dowel inside the whole length.
PVC cement works fine here, but I could have
used 2 part epoxy, or Polyurethane Glue.
(It foams and expands slightly as it cures.)
This is the Four Bar Linkage that willMove the arm. The 4" "Ell bracket" in the
upper right hand corner acts as the shoulder
blade. The vertical bar on the left will be
the forearm. I used 1/8" x 1" aluminum
flat stock for the forearm and "biceps."
Since the lower bar will be doing all the work,
I used 1/8" x 1" steel flat stock. After building
it, I think it was kind - of over-kill.
I assembled each joint with a 1/4" x 3/4" hex bolt. I inserted a 1/4" x 1" fender
washer between each moving part. I used a 1/4" washer and locking nut.
This makes the joint stay together, but remain loose enough to move freely.
All of the extra holes in the "forearm?"
By using a different hole here, you can adjust how far the arm stretches
out, instead of simply shooting up. I know there is a mathematical
solution for all of this, but:
1. Math was not my strong point in school.
2. I like the idea of "adjustable."
3. Four more holes... no big deal.
Here is the shoulder with both arms attached. When the prop is at rest,
both arms will be in the lower position.
When air is applied to the cylinder,
A bungee cord will pull the steel arms
down, thus raising the arms.
It's hard to see here, but the arms are
attached to the shoulder so that they will
extend at about 45 degrees, not straight up.
If you look at the 3/4" PVC "cross,"
you can see that the head will attach
at a right angle to the cylinder. By doing
this, I hope to build the shoulders up,
similar to the "hunchback look."
In this photo, it is easier to see theangle I mentioned earlier. This is the back
side of the prop. (left arm.)
I can still pull straight down on the arms
and cause them to extend. The 45 degree
angle doesn't interfere.
I suppose I could have used a pulley
on each shoulder, and had each arm
stretch straight out, but I think this
will look better as the prop jumps .
I applied expanding foam to the inside
of a latex mask, thin layers at a time.
about mid-way I inserted a 3/4" PVC
"tee" with a short piece of pipe
sticking out the back. I inserted this
into the front part of the 3/4" PVC
"cross." I didn't glue it, and I probably
won't. I will, however, drive a screw
through the joint.
(I can change heads next year.)
There is one more thing I should
point out...
Directly above the "elbow,"
I added an extra bolt and 4 washers.
This acts as a limiter to how far the
"elbow" folds. Putting the bolt here
ensures that it will not interfere
with the movement of any joints.
I hooked everything up and tried it out.
The prop lifted SLOWLY at 10 p.s.i.
At 25 p.s.i., this prop reaches full height
in about 1/2 second. I'm sure the weight of
the body will slow things down a bit.
I used two 60" bungee cords, one on each arm.
They act as anti- spin devices, otherwise, the prop may turn itself around
after a few firings. Also, by using two different cords, I can adjust the amount
of pull applied to each arm independently. ( more adjustment.) Finally,
using two separate cords, I was able to form a tripod- like support
system at the base. At full extension, the arms reach over 6 feet, so
it may become unbalanced with only the cylinder holding it up.
The bungee cords will do a fine job of keeping everything in line.
