Advanced technology guides pods through concrete maze

Advanced Transport Systems has developed a personal rapid transport (PRT) system that is currently being trialled at Heathrow. These driverless vehicles, or pods, are already taking British Airways staff from car parks to the Terminal 5 building, with passengers expecting to get the full service by the end of the year. The design of the Urban Light Transport (Ultra) vehicle has cost some £25 million and six years to implement, but despite development of PRT systems going on for some 50 years, none have yet to work, or be proven viable. So what makes this system so different? Primarily technological and computing advances are the enabling factors. Ultra is reliant on innovative control systems and laser sensors for positional, speed and directional information. But they also rely on computer processing power to make millions of calculations a second and autonomously control precise movements as the vehicles navigate through the network of purpose built 1.5m wide concrete guide ways, designed by Arup, laced throughout out the Terminal. Much of the vehicle design has been carried out by ARRK Research and Development. The Essex based company has historically been an automotive supplier and consultant, working with a number of major OEMs in the industry. But, it is increasingly looking to transfer its technologies in to other areas. All in all, many of the components and systems used are commercial off the shelf. However, the innovation came in the integration of all the components with the guidance system to result in a reliable and effective PRT vehicle. Although, Ultra has four wheels, the similarities with a car end there. "Because it is driverless, it requires a sophisticated onboard guidance system to work," says Mike Gilmore, business manager at ARRK R&D. "It actually stays on the guide ways so well that after a while the vehicles starts to leave a single line black rubber tyre mark from repeated use. "As the vehicles use a rather unusual configuration, the design of the suspension and set up of the steering needed to be treated accordingly. So we used software to simulate the movement of the vehicle to understand the suspension and steering characteristics." The vehicle uses double wishbone suspension on both the front and rear made from machined aluminium, as well as standard automotive coil over damper units, joints, bearings and bushes. "It was decided to use a rack and pinion steering gear operated by an electric power steering unit," says Gilmore. "But this set up meant having separate front and rear sub-frames fabricated from aluminium to house suspension mountings, motors, the transmission system and batteries." To minimise the weight and cost of each pod, the main chassis is again predominately fabricated using an aluminium ladder frame. But to add stiffness, but not compromise weight, the team used aluminium honeycomb sandwich panels on both the floors and bulkhead panels. A welded steel tubular upper frame is used to support exterior and interior bodywork, side doors as well as the front and rear hatches. The body panels are constructed of self coloured ABS, and are bonded straight on to the vehicle frame. Large glass screens and windows add a very futurist styling to match the vehicles technological underbelly. All in all, the vehicle weighs around 820kg, and will be driven by a synchronous 7kW AC drive motor and powered by four 45Ah lead acid batteries. This will allow up to four passengers to be driven from a pick up point to a specified drop off point at up to 25mph from ground level rising up to the airport terminals. PRT systems should not be confused with larger and heavier mass transport vehicles that run to a schedule and point to point basis. Instead these run an on-demand service, arriving just as passengers need them. They then take two to four people on a non-stop basis to various destinations via the shortest route available, and are not restricted by set routes or stops. Analysis shows that buses, trams and trains, which are regimented to a schedule, do not meet the demands of passengers which have to wait for the next one to arrive. Additionally, mass transportation systems have any benefit eroded, both economically and environmentally, when they are below a certain capacity. "This is personal rapid transport," says Gilmore. "We think this works out to be 70% cheaper than infrastructure or monorail systems, and the biggest cost saving is that they do not use a driver." Each vehicle operates relatively autonomously, although it is in continuous communication with a central control system to monitor movements so it can override vehicle decisions to improve passenger flow, pick up time or prevent an accident. If the worse does happen, the bumpers are designed to progressively absorb impact energy and limit passenger deceleration. However, the system has undergone over 12 months of extensive testing on a test track in Cardiff without a significant failure. All electric van suits urban use. ARRK has also had significant involvement with other electric vehicles, teaming up with Modec to produce an all electric van. Like its work with the Personal Rapid Transport vehicle, ARRK designed the chassis, brakes, suspension, body and trim, and advised on styling. The in-house team also sourced all third party materials, and fully managed the production and testing of prototypes. Mike Gilmore, business manager at ARRK R&D says: "With Modec, we pretty much started with a blank sheet of paper. We had our vehicle designers doing everything from the chassis to the body, trim and steering with the CAE guys running simulation work in parallel. "The vehicles have a payload of 2,000kg and a range of 150miles. This made them perfect for use in urban and inner city environments. Additionally, a key element of the design to improve its functionality is the small turning circle. The vehicle is available as a chassis cab or box van, and uses a large 'box cassette' battery which is easily exchanged, giving high fleet flexibility to users. Tesco, for example, has brought a fleet for it home delivery vans." Like most companies, Modec wanted to know all the costs from the outset, and know how to reduce them. This meant that ARRK put particular focus on designing the vehicle for the optimal production volumes.