Problem

There are surprises in the Guthrie Theatre's Peer Gynt. Some are in Ibsen's fantastical story. Some are in Tim Carroll's production of Robert Bly's translation, which adds a surprise party for Gynt during which he collapses and imagines himself into the play. And some are in, well, in the floor.

The many scenes unravel in a barn-like wooden structure, with few props. But Carroll and scenic/costume designer Laura Hopkins wanted that barn to have a life of its own. The simple floor begins to shift in Act 2, then undulates, coming to life to symbolize Peer's journey.

Technical director Jeff Dennstaedt and assistant technical director Craig Pettigrew had only a drawing of the deck and a partial model of a floor to go on when they began work. Some 20' to 25' would be stationary, but 21' from upstage to downstage and 38' from left to right would eventually be in motion.

Hopkins wanted three zones of floorboards. Upstage boards would move the most, rippling into the middle, with downstage boards flowing more than rocking. Boards would also be different heights. The floor would have to be solid initially for moving and dancing, and it could not reveal the trick that occurs well into Act 2.

Actors crossing the stage would have to get used to an up-and-down motion; when walking upstage or down, they would need to navigate boards that moved at different paces, as well. It was up to the tech staff to make sure the planks did not gap and create trip or shear hazards, a factor for how high each zone could go.

When a fan asked how the undulating floor works, crewmember Craig Rognholt says that he simply joked, “There are 67 trolls living under the stage that stand up and then sit down on cue.”

If only it had been that simple.

Solution

Dennstaedt and Pettigrew enlisted shop members in research and development. “I cannot tell you the number of ideas we kicked around,” Dennstaedt recalls. These included pneumatic cylinders and lift frames; they worked some out on paper, others on the shop floor. “We weren't looking for the right answer but something to help us move toward the right answer, so we knew what we needed to do next,” Dennstaedt adds. All attempts yielded an idea or two. The first idea they mocked up, a camshaft that would lift each plank independently, turned out to be most fruitful.

They made a second camshaft mockup with three sets of lobes to lift planks to various heights, did some troubleshooting on the floor, fixed glitches, got it running, walked on it, and there it was.

Three zones of boards travel at different speeds, some going up while others go down. Shafts push up near one of the hinge points of a board. The downstage zone had five rows of planks, ranging from 2¼" to 5" high. In the center, seven rows raise to 8", and 10 rows upstage raise to 12".

They had shied away from the shaft idea initially after looking at some of the tortional forces involved. The tolerances would be “so tight it would be tricky… The lineup of parts would have to be dead-on,” says Pettigrew. Could they find ways to get better alignment and still control the degree of tolerance? They decided on UHMW (Ultra-High Molecular Weight) polyethylene pillow blocks, a good, inexpensive way to get a low friction alignment. “We needed to secure the camshaft to the framework that dropped into the traps on stage,” says Pettigrew, explaining why there needed to be a pillow block between every plank's lifting arm.

“The inclusion of some bushings helped by getting a better fit to the shaft with the other components. As we put things together and coupled everything into a line and ran it, we discovered things along the way,” says Dennstaedt.

As they worked, they created parameters to help them solve the problem. First, the planks had to have one point rigidly connected to the floor. This point had to pivot and/or glide. (Gliding produced stable results.) Second, the plank that attaches to the camshaft also had to attach to the floor on a glide to help keep the planks in line and provide the cleanest “scissor” action across the deck. Third, the hinge points had to have no pinch points. Fourth, even minor adjustments of the hinges to the cams, guides, and pivots would significantly affect the height and motion of the undulation. Next, the pivot and guides needed to be parallel to the camshaft in order to move each row of planks in a line. Finally, since the center plank (US/DS) in each zone of the deck had to raise the highest, that plank needed the hinge point the farthest from the cam, thereby creating the biggest lever arm on the middle plank in each zone. The boards that had to raise the lowest needed the hinge closest to the cam.

They realized the planks had to attach to the camshaft. “When we tried just using casters as rollers on the underside of the planks, we found there was nothing to ensure that, if you walked on one plank, the next plank in that row didn't pop up uncontrolled,” says Pettigrew.

To create a wave motion, three camshafts would control the three zones of planks. Three motors control the operation, independently for each deck zone, adjusting the sequence for a variety of undulating looks.

While watching on monitors from under the stage, Rognholt operates a Hudson Scenic hydraulic valve controller and three Hudson Scenic Digital Winch Units, which control the drive motors and, therefore, the speeds in different zones, including acceleration and deceleration.

Over 7,000 pieces make up the 21'×38' deck, divided into three sections: 10 rows of 12' planks driven by a hydraulic motor upstage, seven rows of 10' planks driven by a hydraulic motor center stage, and five rows of 8' planks driven by an electric motor downstage. “We found after load in that the action of the actors on the deck was more intense than we were originally planning,” says Pettigrew. “This caused us to add six pop-up frames to reinforce the deck. They are parallel frames that rise up under the deck pneumatically. These were installed with an interlock system that will only allow the deck to run if the pop-up frames are disengaged and clear.”

They manufactured most parts in-house, a labor-intensive process. “We pretty much had the whole thing set up in the shop, including the drive motors themselves,” says Dennstaedt, “and we waited for the other shoe to drop when we took it to load in.” The install went smoothly, something both tech directors credit to the Guthrie carpenters who realized the challenge and embraced it.

Check out the process, documented in these videos: Shifting a wooden floor

If you have encountered a problem while designing or building a concert, event, exhibit, or play, please tell us about it at davi@comcast.net.

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