BASICS / CAMERA CRADLES /
DAVID HUNT AUGUST 9, 2002(Pronounced pick a vay, rhymes with weigh)
A VERY BRIEF HISTORYNamed after its French inventor, early 20th century. Forgotten and rediscovered late 20th century.
Purpose of the PicavetPicavet at Work Most KAPers attach the camera to the kite line and not the kite. The angle of the line to the kite is constantly changing. To provide a level platform for the camera KAPers use one of two devices; the pendulum, or the Picavet. The animated GIF below shows the leveling principle of the picavet. The camera cradle hangs beneath the Picavet cross from a bolt that is fastened through a hole at the center of the cross. The picavet cross provides a level platform for the camera cradle. Camera cradle design is covered on a separate page.
PICAVET VS. PENDULUMLet me begin this section with a quote from Brooks Leffler, taken from Cris Benton's discussion page, 7/1/1998.
"I've built maybe 25 or so Picavet rigs, and maybe five with pendulums...I found the pendulum much more complex and time-consuming to build, more expensive, and much less compact to transport. I can see that if you're launching from a canoe as Henry Jebe does in Alaska, a pendulum is the only way to go, but for me, I remain a diehard Picavet Person."At first glance the Picavet looks more complicated than the Pendulum, but as Brooks points out this is not so. The Picavet has an inherent dampening effect as part of its design. As the kite line changes angles a Picavet moves to the new level position and stops. A Pendulum, without any dampening added to it, will swing back and forth until it finally settles in its new rest position. The lines of the Picavet also provide dampening of wind induced vibrations on the kite line.
Start with the Picavet, use a Pendulum only if you have a specific need.
THE PICAVET PARTSThe Major Parts of the Picavet Refer to the adjacent labeled image.
- Attachment Points (A & B)
These are the two points where the picavet is attached to the kite line. I use two small chrome-plated welded rings. Many use two pulleys or double pulleys at each attachment point but pulleys at the attachment points are not needed and do not improve performance (see Page 2). The Line Tree section below show how the rings are attached to the kite line in the field.
- Washer or small split ring.
The purpose of the washer is to control the rotation of the cross on the axis that runs perpendicular through the center of the face of the cross. Without this ring you will have trouble every time you panned your RC rig.
- Eye Bolts or Pulleys
Either will work. Pulleys respond quicker to changes in the kite line angle at the expense of greater weight and/or higher cost (See Brooks' Notes).
- The Cross
Picavet crosses range from 3" to 12"(76 to 304mm). There is no know advantage to a larger cross. A light camera rig will benefit from a smaller cross, so use a smaller cross and save weight.
(See page 2 for an optional discussion of Picavet principles.)
The cross does not have to be in the shape of a cross. Some KAPers have used rings or squares with the Eye Bolts/Pulleys evenly space around the perimeter. The cross is typically made from 1/16" aluminum or model aircraft plywood.
When you read Brooks Leffler's letter at the bottom of the page, you will see that he uses 80# braided Dacron. I have used heavier line to prevent the line from jumping off the pulley wheels and fouling between the wheel and pulley housing. Lighter (thinner) line will slip through eye bolts easier.
- Line Length-
When you hold the two attachment points together in one hand you want the Picavet cross to hang down no more than 4 feet (1.2m). This makes it easy to handle the picavet with one hand in the field. Since there are 8 lengths of line between the cross and the attachment points, you do not want more than 8 X 4 or 32 feet (9.8m) of line. This falls within Brooks' guideline of 5-6 arm-spans.
- Line Length-
5 Inch Picavet with Pekabe Blocks
CONSTRUCTING THE CROSSFigure 1 Figure 2 A picavet cross can be cut from a single sheet of 1/16" (1.6mm) thick aluminum like the picture above, or if you only have narrow strips of aluminum then cut two pieces of equal length and bolt them together in the middle. Leave enough space around the center hole for the wing nuts that are used to fasten the camera cradle to the picavet cross. Modeling plywood can also be used to make a picavet cross (see LASS).
If you are going to use eye bolts secure them to the ends of the cross with nuts and lock washers. Align the eye bolts as shown in the illustration in the next section. I attached the pekabe pulleys in the picture above by drilling two small holes and using small wire ties to hold them in place. Remember that the pairs of holes should all align in the same direction. (Figure 1).
Figure 2 shows the typical hardware used to attach the camera cradle to the picavet cross. The cross would go between the two lock washers.
THREADING THE PICAVET LINEPicavet Threading
Click on Drawing to see Animated GIF
of threading sequence. (238KB) The line starts and ends at the same attachment point. You can begin by tying one end of the line to R1
The line only passes through the washer (Rc) on the first two downward passes of the line. You should end up with only two sections of line passing through the washer.
The line ends at the same ring it started from. You can tie each end of the line to the ring or you can tie the ends together and get the same results.
All 4 Eye Bolts (or Pulleys) should face the same direction.
Eye Bolt / Pulley Orientation
Using the Diagram below,
The threading sequence is:
The threading sequence is:
THE BEUTNAGEL DRAWINGThe drawing below, by Ralf Beutnagel, has been circulating around the KAP community since 1995. You will see it on various KAP web pages and in the Aerial Eye (1:4 fall '95). This is the same design we have been discussing above, except Ralf shows pulleys at the attachment points in place of rings.
The Standard Picavet
A1 - 1 - B1 - R - 4 - A2 - R - 2 - B2 - 3 - A1.
At first glance Ralf's sequence may seem different than the sequence in the previous section. They are actually the same sequence with different starting points. I personally have never used pulleys at the attachment points, except to experiment and determine that they are not necessary. Instead I use a small ring at each attachment point. A more detailed discussion of the principles of picavet operation can be found on page two.
Notes About Using Pulleys
Pulleys are not necessary. (See Page 2 and Brooks Leffler's Comments below.)
Pulleys at the attachment points are a waste of money. The line does not run through the pulleys at the attachment points once the picavet has been attached to the kite line and the cross is leveled.
Pulleys on the cross allow the picavet to respond quicker to changes in kite line angle than a cross with eye bolts. When using eye bolts, the friction with the line must be overcome before the cross will level. A heavier rig and/or thinner picavet line will cause the picavet to respond quicker.
Lighter rigs benefit more from the use of pulleys on the cross than heavier rigs.
Lighter rigs benefit from the use of smaller crosses.
PICAVET ETYMOLOGYFigure 3 Figure 4 Figure 5 Figure 6 The Aerial Eye article (1:4 Fall '95) by Beutnagel, Bieck, and Böhnke refers to the Standard Picavet drawing above as the classic picavet, but the picavet that was used by Pierre Picavet in 1912 was in an X configuration.
In an effort to bring some historic consistency to the picavet naming process, and to introduce some shorthand that simplifies the written discussion of the various picavet variations, I offer the following definitions; (The shorthand is not my invention but was the result of a discussion thread on Cris Benton's discussion page dated 6/10/02)
- Standard Picavet-
This is the picavet in the image above and described in all the sections found on this page. In Figure 3 one arm of the picavet is in-line with the kite line and the other line is at right angles. You can assume that someone who refers to a picavet, but does not designate a particular variation, is referring to the Standard Picavet. This is the most widely used variation. Acceptable shorthand is
- Classic Picavet-
This the picavet used by Picavet himself. As can be seen in Figure 4 the picavet cross forms an X-shape in relationship with the kite line. Acceptable shorthand is "X picavet".
- Rendsburg Picavet-
This is a variation descibed in the AE article mentioned above. The cross is H-shaped and the acceptable shorthand is
"H picavet" (Figure 5).
The H picavet is another way of making the X picavet. See a related article related to the namesake of this variation.
- Triangular Picavet-
Also first describe in the AE article above, the main cross is T-shaped. Figure 6 shows the relationship of the T cross to the kite line. Acceptable shorthand is "T picavet".
ATTACHING THE PICAVET TO THE KITE LINE"Line Tree" Attached to Kite Line
This is the simplest method to connect a picavet to the kite line. All you need is 6 inches (15.24cm) of coat hanger wire and a pair of needle-nose pliers. Bend the wire to the shape shown. You can use snap swivels between the line tree and the attachment point rings or you can bend the wire directly around the rings.
The line tree will not slip. I have had my kite straight overhead with little tension on the line and my 1.25# (567g) rig did not slip at all. Part of the trick is to orient the weight bearing end of the line tree towards the kite.
To secure the line tree to the kite line, hold the line tree parallel to the kite line and wrap the kite line 5-7 times around the line tree.
Attach the next line tree so that an equilateral triangle is formed by the kite line and the picavet lines.
- Cheaper, Lighter, and easier to make than Brooxes HangupsTM
- Easier to use than Prussik knots.
- Will Not Slip.
Once the rig and picavet are attached to the kite line you may need to manually level the picavet cross the first time. This is the only time the picavet line will slip through the Attachment Point Rings. Once the cross is level the picavet line will only move through the pulleys or the eye bolts.
PICAVET STORAGEPicavet Storage Organizer I've seen many ways to store a picavet, here's the one.
The organizer was made with a 5 inch length of 1 X 2 lumber. A snap swivel is fastened to each end with screws. An eye bolt is attached through the middle of the length of wood. The carabiner is the small inexpensive type frequently found next to the register in hardware stores.
To use the organizer;
- To store the picavet.Clip the Attachment Point Rings with the snap swivels.
- Starting on the cross end, Chain Knot the picavet line.
- The final loop of the Chain Knot is clipped with the carabiner. The picavet is ready to store.
- To use the picavet, first attach the cross to the rig.
- Remove the loop of line from the carabiner.
- Let the weight of the rig undo the chain knot.
- Remove the Attachment Point Rings from the snap swivels and you are ready to attach the cradle to the kite line.
Brooks Leffler's Comments About the PicavetMarch 23, 2002
Walter Anderson raised a good point in his article "My First Experience with KAP," regarding the dearth of details about the Picavet suspension available on the web.
Let me contribute a few basics, based on building many rigs using the Picavet suspension.
First, I use about 5 - 6 arm-spans (precision craft this) of 80 lb braided Dacron line. Picavet's original 1912 design called for something like 80 feet of line, but the scale was about double the size of rigs today. I started with 40 feet, but after a hypothetical question online by somebody now forgotten, I reduced it by, say, 6 - 10 feet. It's easier to install and store, and unless you use a near-vertical kite, there's no real benefit from the extra length.
Second, Picavet himself didn't use blocks or pulleys on the X. He didn't see the need for anything but eyebolts. But I'll admit that those lovely little PeKaBe blocks are sure smooth.
Third, Picavet's design works whether you have an endless line or not. For a while, I even tied it at the two upper connection points so it didn't run through them at all, but that works well only if you always install the rig with the suspension points the same distance apart.
Some of the German purists do a sleeve splice so the line will run endlessly through the blocks, but I just tie a plain old loop knot in one end of the line, slip it into a split ring at the upper flying line connector, then lace the line back and forth and finish it by connecting the bitter end to the same upper split ring with another loop knot.
Finally, despite my use of my brooxes hangupsTM, you don't need anything fancy to hang the Picavet system from the flying line -- the German aces all use the Prussik knot, made with a very simple 4" loop of line.
Both knots referred to here are illustrated in my knots article in vol. 5 #1 of The Aerial Eye.