What is in this article?:
- Disney Engineer Tames Monster Project
- Early Development
Most of us only experience the finished version of theme park attractions without even a hint of the stages of development that were necessary to turn concept into reality. Revealed here are some typical and not-so-typical experiences of one engineer assigned to a special project at Disney's World's EPCOT Center.
Perhaps the most impressive accomplishment of the project was the short time in which a one-of-a-kind monster was developed. “Emmett Peter, manager of Engineering Services, brought four key engineers together and had a brief discussion,” recalled Lenz. “He told us what we had to accomplish, and outlined responsibilities for each of our respective areas. I was assigned the design of the entire hydraulic system, as well as the main structure beyond what was being supplied. Staff Engineer Mario Scarabino headed a fantastic team of engineers and designers assigned to specific parts of the project. That team and the fabrication team in Central Shops worked virtually around the clock until completion.
“I think the most amazing technological feat about this project,” continued Lenz, “was that in just 29 days from the day I started working on it, we had designed and fabricated the system, built the majority of the equipment, and installed enough hose, tubing, actuators, valves, and electrical controls to run our first system test.” Aside from the cooperation and dedication of all involved, an innovative idea was the key to this success.
The design team studied the concepts established by Creative entertainment and determined that the monster would be able to turn left and right and pivot forward and backward on its base. A joint at the end of an extension from the base (serving as framework for the lower torso) would allow an upper extension (framework for the upper torso) to pivot up and down. A final joint on the end of this upper extension would allow the head to pivot up and down in a nodding-type motion. Provision for pivoting the head left and right on top of this joint was integral to the head being furnished.
These four axes of motion (base turning, lower extension pivot, upper extension pivot, and head pivot) are identical to the movements of an excavator arm on a backhoe. The design team realized that using an existing backhoe arm would speed up the production process considerably by eliminating many design and fabrication steps. Their task then was to find just the right excavator arm that would handle the loads, speeds, and motions required. Their search led to a John Deere 490D backhoe.
“We decided to use that structure because it was about the right size we needed and had proven to be able to carry loads of the type and magnitude that we were working with,” explained Lenz. “The fact that it was an off-the-shelf item certainly made it attractive time-wise. Fred Sollie, an engineer with the Live Show Design Div., did some background work on the 490D. He rented a John Deere 490D backhoe, brought it on site, and all the engineers that were involved in the project got into the tractor and took turns running it just to get a feel for what kind of a structure we were dealing with. Once the team was assembled, we each took off in our own given direction.”
Forgotten movie star aids project
Sometimes improvisation is an engineer’s greatest tool. Faced with a six-week deadline to design the structure and hydraulic system for the fearsome-looking creature pictured on the front page of this article, Matt Lenz, senior engineer, had a system ready for testing only in 29 days. But one obstacle remained: How do you accurately test the system when the nearly 3/4-ton head is not scheduled for completion for a few more weeks? The answer: Make do with what you have.
Disney’s Ride & Show Engineering team found a discarded prop that seemed to be about the same size and weight as the head — the hulk of Herbie the Love Bug, a 1960’s Volkswagen beetle. After sustaining damage, it had been taken out of commission months earlier and was stored in a backlot to await its fate. Senior Engineer Jeff Hudson verified the weight distribution of the head under construction, and then strategically welded additional steel into the VW and made modifications to its frame in order to bolt it onto the monster body. Once the heavyweight VW was mounted, dynamic tests were conducted that verified the design goals had been achieved, Finally, the real head arrived to replace Herbie and the show opened on schedule.
Construction and Operation
The quick turnaround essential to the project meant that some original design requirements were revised. Lenz said, “We sat down with the people from Creative Entertainment to establish what the monster had to do as opposed to what they’d like it to do, time permitting. This allowed me more freedom in designing — a luxury that probably every engineer likes to have. We were almost defining our own specifications for speed, pressure, travel distance, and so on, as the project progressed. About the only constraints we had were weight, and the pressure and flow capabilities of the HPU. Of course, one of the other team members verified everyone else’s work, so nothing was overlooked.”
The backhoe comprised the lower body and the torso of the monster. The joints worked much like a shoulder at the base, an elbow in the middle, and a wrist at the top. Lenz revealed, “We figured the backhoe’s pivot points could take any side loads generated, but an engineer verified every structural element that we were using. I also was involved in determining the static and dynamic loads simply because these figures were needed for designing the hydraulic system and selecting components. If we weren’t satisfied with the integrity of any material or element, we redesigned that particular component.
“I designed my own redundant hydraulic system to integrate with the John Deere backhoe structure. I took out everything hydraulic that came on the structure and put in my own system, including cylinders and proportional valves. One of the first things I did was make real rough estimates of cylinder size, because the cylinders would dictate the size of all other hydraulic components in the system. We knew what the structure would basically look like, and we had some data on the masses of the head and the John Deere elements.
“The cylinders carried the longest lead time of all the elements, because they needed some modifications for mounting. I decided on NFPA-style [tie-rod] cylinders, because they are so readily available. We might have to wait to have modifications made, but we wouldn’t lose any time waiting for the cylinders themselves. After getting a rough size of the cylinders, I verified dynamic loads. To do this, part of our team locked ourselves in a room with representatives from the hydraulic component manufacturers and distributors to grind out the specifications. The cylinders could then be resized based on these dynamic loads. From that point on, everything almost fell right into place. We didn’t have a day to waste, so once I finished calculating dynamic load and sizing the cylinder, I passed my data on to the manufacturer’s rep, who would verify the size of the valves based on the speed, flow, and pressure. It worked very well, almost like an assembly line.”
Motion and Control
Lenz decided right away to use electrohydraulic proportional valves and designed them into the system at the very beginning. The system had to run smoothly, ramping up to constant velocity, then ramping down. So one of the first things he did was establish velocity curves for each of the functions.
In the theme park business, viewers often can distinguish good characters from evil ones just by the way they move. Good characters usually have smooth, fluid motion that is pleasing to the eye, while evil characters move in harsh, almost jerky motions. Even though the monster is one of the bad guys, the designers wanted it to have smooth smooth motions, possibly to give it the moves of a live creature even though it obviously was a machine. Lenz explained, “I relied on adjustments in the valve amplifier cards to make motions start and stop smoothly and to control how much basic proportional control we actually got. I had used this technique before, so I could vouch for its success and versatility.
The monster itself encompassed eight axes of hydraulic motion:
1. left and right turning at the base,
2. up and down pivot at the base,
3. up and down pivot at the joint between upper and lower body sections,
4. up and down head nodding at the top of the upper body (a platform that replaced the bucket of the backhoe, upon which the head was mounted),
5. left and right head turning (integral to the head),
6. head tilt (leveling), which is done automatically
7. left set of wings in and out, and
8. right set of wings in and out.
The wings were synchronized to move forward and backward at the same rate. The hardware encompassed two separate systems: two valves, two sets of cylinders, and two controls that run in parallel. Rather than using a lot of complicated hydraulic or electronic controls to keep the wings synchronized, Lenz again relied on tuning the valve driver cards and flow controls so that one input signal produced synchronized motion of the left and right blades. If one side tended to move slower than the other, tuning one of the cards would speed up or slow down one set of blades.
Two puppeteers operating six different multiple-function joysticks run the monster. Because the character is not run by a computer, every show is live and unique. “Operating the monster by a puppeteer was one of the original requirements of the show and was a big reason the team was able to get the project up and running so quickly,” Lenz explained. “However, the controls engineer, Kevin Schultz, implemented a sophisticated envelope-protection scheme to prevent motion in certain areas. His design depended on linear feedback sensors within the cylinders sending data to a PLC that he programmed with the operating envelope. The complexity and accuracy of the envelope protection was amazing.”
Matt Lenz, senior engineer assigned to Ride & Show Engineering Div., Walt World Disney Co., Lake Buena Vista, Fla.; Thom Pawlyn, market sales specialist, animation/simulation, Vickers Inc., Troy, Mich.; and Brian Poole, sales engineer, Hydraulic Supply, Orlando, Fla., provided technical details for this article.