Sprint drives Vampire ride

09 February 2010

An exciting application of control technology saw UK theme park, Chessington World of Adventures turn to Sprint Electric for DC drives to use on its rollercoaster. Trains on the Vampire ride at the south-west London theme park and zoo make an average of 720 laps of the track in one day, causing a great deal of strain on the DC motor control system.

The Vampire ride is a swinging, suspended rollercoaster at Chessington World of Adventures
The Vampire ride is a swinging, suspended rollercoaster at Chessington World of Adventures

The Vampire ride became the UK’s first suspended rollercoaster when it opened in 1990 and the only coaster to fly above tree height. During the summer season, the Vampire ride attracts 17,000 visitors a day.

Three trains make, on average, 720 laps of the track over an eight-hour day. This creates a substantial workload for the ride’s DC motor control system. The ageing control system was becoming costly in both maintenance and downtime. Chessington World of Adventures needed to improve the ride’s reliability ahead of the summer’s peak-season.

Chessington World of Adventures had two options: Redesign the control system to use AC motors and AC drives, or keep the existing DC motor control system and retrofit it with modern DC drives. Redesigning with AC technology would mean a lengthy and costly Health and Safety review. Keeping the already installed and proven DC technology proved both easier and more cost effective.

System integrator B & G Controls of Sittingbourne, Kent, was contracted by Chessington World of Adventures due to their knowledge of fairground applications. B & G Controls chose DC drives from Sprint Electric because they had previously worked together on another demanding ride application at Chessington World of Adventures.

David Garwood from B & G Controls explained: “Two 430 Ampere PLX digital DC drives were installed to control the Vampire’s flight. Each flight has many twists and high-speed turns, but the two lifts create the serious demand. To raise the three trains and 24 passengers, the drives operate at 90 per cent current for the first lift and 100 per cent current for the second.”

To make the ride’s load-run-disembark process a smooth one for the park’s visitors, the PLX has to interface with an existing SLC-500 series PLC from Allen Bradley. “The PLX DC drives’ software made it possible to re-program inside the drive, some of the signals coming out of the PLC to suit the application better. Signals such as Field o.k. and Tacho o.k. required logic function and timer function PLX application blocks to re-create what the PLC needed of them,” explained Sprint Electric’s research and development director Aris Potamianos, who helped with the software integration and commissioning.

Other PLX safety features ideally suited to this application are the drive’s coast-stop input and the ability to revert automatically from tachogenerator speed feedback to armature voltage feedback. The PLX's coast-stop input ensures the ride control can effect an almost instant isolation of the drive from the rest of the process in the unlikely scenario of hardware or software failure inside the PLX. The coast-stop input forces the drive to cease supplying armature current to the motor irrespective of drive operating conditions.

Another useful safety feature is the PLX’s ability to automatically revert from tachogenerator speed feedback to armature voltage feedback in case of mechanical or electrical damage to the tachogenerator or its connection medium to the drive. The drive will give a warning of this failure to the PLC but it will continue to be under closed loop speed control until the next convenient stop instance when the fault can be attended to.

With the installation and commissioning complete, Chessington World of Adventures’ engineers said they were pleased with the re-vamped control system, having noticed the ramp up to full speed is a lot smoother now.

Garwood concluded: “The test runs during the park’s closed season were really successful. We were all looking forward to seeing the improvements when the park opened again in the summer.”

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