Vampire ride runs smoother with DC drives

Chessington World of Adventures, a popular theme park and zoo in southwest London, offers 25 different rides and attractions. One of the most famous is the Vampire ride. It 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 thrills adrenalin junkies of all ages – it is one of the few rollercoasters Europe-wide available also for small children, starting at a height of 1.1 m. At peak periods, 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 last summer’s peak season.

It 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 the companies had previously worked together on another demanding ride application at the theme park.

“Two 430 Ampere PLX digital DC drives were installed to control the Vampire’s flight,” explains David Garwood from B & G Controls. “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% current for the first lift and 100% current for the second.”

To make the ride’s load-run-disembark process a smooth one for the park’s visitors, the PLX had to interface with an existing SLC-500 series PLC from Allen Bradley. “The PLX DC drives’ software made it possible to reprogram, 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,” explains Sprint Electric’s research and development director, Aris Potamianos, who helped with the software integration and commissioning.

A PLX safety feature suited to this application is the drive’s coast-stop input. This 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 tacho-generator speed feedback to armature voltage feedback in case of mechanical or electrical damage to the tacho-generator 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 addressed.

With the installation and commissioning completed, Chessington World of Adventures’ engineers were pleased with the revamped control system, having noticed the ramp up to full speed is a lot smoother than before the retrofit took place. MRO