What is in this article?:
Ride simulators are fun, but nothing beats a thrill ride for striking fear into the hearts of participants.
Plenty of power
Providing power for the XScream are two hydraulic power units, which were provided by Intermountain Hydraulics & Automation, Smithfield, Utah. Jeff Loosli, of Intermountain, says each of the 50- hp hydraulic power unit uses a Parker Hannifin PVP60 axial-piston pump. These variable-displacement pumps feature pressure compensation to maintain system pressure and are sized for a maximum displacement of 60 cc per revolution. Loosli says this translates to roughly 28 gpm when driven at a nominal speed of 1800 rpm.
But high-velocity moves demand more than the combined 56 gpm the pumps can deliver. Therefore, flow from each pump is supplemented by a bank of five accumulators — four 10-gal. and one 212- gal. To minimize accumulator size, 14 gas bottles are incorporated into the accumulator network to store compressed gas.
When the attraction is idle or in a low-flow demand mode, the pumps continue running to charge the accumulators with pressurized fluid. The accumulators act as springs to store potential energy. But instead of storing mechanical energy as a spring does, they store fluid energy.
Once the accumulators are fully charged to specified pressure, the pump’s pressure-compensator reduces its swashplate angle to where displacement is just enough to maintain system pressure. But once a ride cycle begins, flow demand causes the pump’s displacement to increase to accommodate the flow. When flow demand exceeds the pump capability, system pressure drops, so pressurized fluid flows from the accumulators to supplement pump flow. Ultimately, then, the accumulators allow using a much smaller pump. This reduces the physical size of the pump and peak energy demand.
Sophisticated motion control
As would be expected, controlling motion of the X-Scream requires more than having an operator simply move a joystick to shift directional control valves. Instead, motion is controlled through a computer that commands two Size D10 proportional valves. Because of their large size, these valves are controlled indirectly through a solenoid operated pilot valve. A small linear displacement transducer sends a feedback signal of the main valve’s spool position back to the computer for tight control. This is in addition to the motion control loop closed by the resolvers mounted to the beam.
Harris says the computer stores more than 100 different ride profiles that can be run at random, or the operator can select a specific profile based on the whims of the occupants. Daredevils may opt for the most terrifying ride the XScream can muster, while others may find the dizzying height frightful enough and choose a ride that is more tame.
Air cylinders bring relief
The X-Scream provides two elements of fear (see related article beginning on page 24). First, most riders would have an inherent fear of the car somehow falling off the track and plummeting to the ground far below. As if that thought isn’t scary enough, another fear is that of falling out of the seat.
Gary Bird, mechanical engineer at Interactive Rides, Logan, Utah, says X-Scream has four independent locking mechanisms on each chair and titanium restraining bars. “These restraints lock in place through a purely mechanical pawl-and-ratchet mechanism. Once they are locked in place, there’s no way to release them without actuating the pawl lever.”
To release the pawl, explains Bird, when the car returns to the home position, the ride operator indicates an all-clear situation on the control panel. The control computer then signals 16 normally closed solenoid valves (two for each seat) to open. Each of these valves routes compressed air to a double-acting cylinder that releases a pawl lever.
“Every safety-related system on the X-Scream has at least one backup, so we use two independent restraint systems for each seat. Each restraint has its own pawl lever, which is why we need two cylinders.”
If electrical power is lost, or the car cannot be brought back to the home position, the valves cannot be actuated. So in the extremely rare situation where the air cylinders cannot be actuated, a mechanical release can be activated to release the pawls.
In the end, when the car is tucked away securely at the loading area, the familiar ka-chunk of the air cylinders surely brings a sigh of relief to passengers grateful to be back on the ground — or at least 100+ floors above it.