A challenging weekend

Wearing sunglasses and a large-brimmed sun hat, London Underground’s head of train systems engineering is standing in the rain in a Leicestershire field. Writes Nigel Wordsworth

Close by, the professor of Railway Engineering at the University of Huddersfield is looking worried, the director of Future Railway is trying to get comfortable on a wooden seat, while the commercial director of Transport Scotland, looking dapper in a bow tie, is checking his watch.

It must be the Institution of Mechanical Engineers’ (IMechE) annual Railway Challenge.

The Leicestershire field in question, near Melton Mowbray, actually contains the Stapleford Miniature Railway – a long- established and well-maintained 10.1/4” gauge railway that opens to the public twice a year. With almost two miles of track, no regular public visitors to inconvenience, and no infrastructure complications to worry about, it is the ideal venue for the IMechE.

hird occasion

This is the third time that the Institution has run its Railway Challenge. Teams of students, graduates and apprentices from industry and academia are tasked with designing and building a locomotive which has to achieve set performance criteria. In addition, they have to present a business case and explain their designs to a panel of experts.

The specification is changed every year to prevent a successful team from simply wheeling out last year’s design. Previous challenges have included tests of ride comfort, energy recovery and traction performance, and this year a noise test was added.

Philippa Oldham, head of transport and manufacturing at the IMechE, explained: “The Railway Challenge gives students, graduates and apprentices a fantastic opportunity to test their engineering skills and to get a taste of a real business experience.

“The Challenge is run along the lines of a real-life tendering process, and teams have to prepare a business case, finance, design, and build a locomotive from scratch.”

This year’s technology

The teams gathered at the Stapleford Miniature Railway, in the grounds of Stapleford Park, in the middle of June. Four teams presented locomotives for scrutineering (technical checks) on the Saturday. Five entries had been planned, but one – from the University of Sheffield – had simply run out of time. Three of the teams had competed before – Interfleet, which won the first year, 2013 winners the University of Huddersfield, and the University of Birmingham – and there was one new team, from Transport for London but entered as London Underground.

All four used a power source to run one or more generators which in turn powered electric traction motors. However, there the similarity ended.

The University of Huddersfield’s entry looked most like a conventional railway locomotive and had two twin-axle bogies. One bogie was powered by the traction motors using a chain drive, the other was used for a mechanical energy recovery system.

Each axle on the energy recovery bogie had two cages on it with a mechanical spring between them. These cages could be locked to the axle using clutches, and the outer edge could be fixed to the bogie frame using a friction strap around the circumference. By altering the locking mode of each cage, energy could be stored and recovered. For instance, locking one cage to the frame and the other to the axle would wind the spring up as the axle retarded, storing energy in the spring. Reversing the lock and releasing the spring would cause the locomotive to move forward as the spring unwound.

Interestingly, this system made it possible to store and recover energy in either direction. It was a neat idea, although perhaps mechanically a little complicated.

Interfleet’s entry was a much more utilitarian shape, being a box which tapered at each end. It looked similar to that used in previous years and was the same frame, although heavily modified.

Team leader Emma Taylor explained that two vertically-mounted 5kW motors had replaced the four horizontally-mounted 750W devices used previously. The transmission was new and used bevel gears and a chain drive. A new control system stored energy during braking into super- capacitors.

New dampers had been added to the secondary suspension to improve ride comfort and a new outer casing was insulated from the frame to reduce noise transmission.

As in previous years, Birmingham did not use a petrol generator but had a hydrogen fuel cell. This was wonderfully quiet so the team was looking forward to the noise test.

Rob Ellis, the team leader, pointed out that although the outer shape was similar to previous years, being another tapered box, the interior was completely different. This locomotive doesn’t have a unitary frame, instead it is built using a modular system so everything could be easily changed as the design developed, a feature that team member Ivan Krastev was particularly keen to show off.

The Birmingham design used only two axles. This was explained as representing one bogie of a larger system rather than a complete locomotive in itself. The two axles had passive steering of up to 5 degrees to cope with the tight radii on the Stapleford track.

This year, the motors were nose-suspended. Rubber bushes had supplemented conventional springs to improve ride comfort and yaw stiffness had been increased.

Novel design

The new entry was London Underground. It was even more of a functional box, strictly rectangular and looking quite large. In fact, it was too large and was outside of the gauge in the specifications – a confusion over static and kinematic gauging apparently. Whatever the reason, the team lost points for it.

The locomotive was smartly presented in blue and white livery – courtesy of vinyl offcuts from the Central line. Under the skin was a complete industrial petrol-driven generator, still in its frame, which powered the traction motors directly.

However, the novel thinking was in the braking system. In fact, as team leader Luke Foy explained, the locomotive had three braking systems – a rheostatic system for regular use, an emergency friction brake, and the energy- recovery system. This was quite novel for the competition and everyone was interested to see how it would work.

The basic design was hydraulic. A pump attached to one axle on the front bogie drove hydraulic fluid around a closed loop, as did a hydraulic motor on another axle on the rear bogie. This may seem to be a pretty pointless exercise, and in normal running the whole system just freewheels. However, when recovering energy, this hydraulic fluid is pumped into an accumulator which contains a diaphragm. On the other side of that diaphragm is nitrogen gas, pressurised to around 30 bar.

As the hydraulic pressure increases, so does the pressure in the nitrogen, storing energy. When the flow is reversed, the nitrogen expands, forcing the  hydraulic fluid back out of the accumulator from whence it is channelled to the motor, propelling the train forward.

The team was made up of both graduates and apprentices, and all had played their part. In fact, while Fergal Stranney and his team had grappled with the hydro-pneumatic energy recovery system, which was an idea they had seen used on a smaller scale in a bicycle by the University of Michigan, one of the apprentices had been designing the emergency brake.

Bookwork

While scrutineering was taking place, representatives of the various teams had to report to the station building to make their presentations. This challenge simulated a design team making a financial case for their products to be developed and to ‘sell’ the idea to a potential customer. Ten minutes was allocated for the presentation itself, using PowerPoint on a laptop to make the case, and then a further ten minutes for questioning from the panel of independent judges.

Three of the teams had done this before, one or two even included  previous participants. However, London Underground, as the newbies, didn’t know what to expect. Long faces emerged from the meeting, and there was talk of at least getting one point for spelling the name of the team correctly.

The first day’s running

After scrutineering, the teams got in some much-needed testing on track. Some had found time to try out their locos on other tracks close to home, others had done very little so every moment of running was crucial.

There were the inevitable teething troubles. The London Underground entry was alleged to have failed inside the tunnel and had to be rescued. In fact, it was in the cutting outside, but still, a few anxious moments ensued as the fault was traced to a loose pneumatic fitting.

Later in the day, the teams took part in the first challenge which was for ride comfort. An accelerometer was attached by the judges to each vehicle and then it was driven around the loop of the track around the far side of the lake. As the ride was likely to improve at slow speed, each team had a maximum time of 8 minutes to make the trip.

This caused the first drama of the weekend. Huddersfield set off to do its run and didn’t reappear. One of the clutch bearings, which fix the spring cages to the axles, had seized. As the loco has four such bearings, there were worried faces amongst the Huddersfield team.

There was no way the loco could return to the station under its own power, and with the seized bearing it couldn’t even be towed, so spanners were produced and time was taken. This meant that London Underground was delayed taking its run and, when the accelerometer fell off partway round, it was decided to postpone that element until the following day.

Sunday dawns

Sunshine and showers was the forecast for Sunday. The day started with the former as spectators either hiked to the Haven, site of the day’s tests, or went out on a steam-hauled passenger ‘special’.

London Underground had a trouble-free run for the Ride Comfort Challenge this time, but Huddersfield, who were making a second attempt, had a recurrence of their bearing gremlins. Taking over ten minutes to complete the eight-minute course, that was the end of their participation which was a great shame for the team which had won the year before.

The track was then made ready for the other Challenges. Locomotives would run out to the Haven and around the loop. They would then stop just before the bridge over the lake spillway. When instructed by the ride-aboard judge (David Clarke), they would speed up to no more than 15km/hr and then brake to a halt in front of judges alongside the lake just before the end of the loop. Once stationary, the train’s position  would be marked and it would be released, just using the energy recovered in braking, to see how far it went.

Depending on the system employed, the judges had to take initial and final readings to make sure that no additional energy was used and that the train hadn’t exceeded the 15km/hr speed limit. In the course of the day, both occurred and the offenders were sent back to do it all again.

Once the Energy Recovery Challenge was complete, the competitor ran forward to the start of the gradient up to the tunnel. From a standing start, the time taken to climb the hill was recorded and formed the basis of the Traction Challenge while noise readings were taken both at the start of the climb and at the top for the Noise Challenge. Again, a team could make a second attempt but each was limited to only 40 minutes to complete all three tests.

Interfleet were first to come around. Stopping as required, the energy recovery run went to plan. However, when released the locomotive only managed to move just over one metre using the recovered energy in the super-capacitors. The team was surprised, six metres had been achieved in testing. The judges consulted and there seemed to be a loss of energy while the loco was just standing still, and even a loss as it was moving before it started braking.

The team backed up to try again, and there was a slight improvement but only to two metres. Lots of head scratching ensued.

To make matters worse, a short shower of rain dampened the track. As the loco started up the hill, the team claimed that they experienced wheelspin which affected performance. Sanding is not allowed in the competition, but perhaps some dry towels could have been forthcoming?

Present in spirit

The sun was soon back out and, watching proceedings from deck chairs, the Sheffield team was contemplating what might have been. Martin Evans, Sheffield’s team leader, explained that the project only really got started after students had returned the previous October. It had been decided to have all of the four years’ represented with two PhD students heading up the team.

By the time the design was done the undergraduates had to break off for exams, so build had only commenced about four weeks previously. Components had been delivered, but nothing was yet finished. Still, that would give them a flying start for the 2015 event.

The current design uses a petrol generator and an AC/DC converter to power DC traction motors. A separate third-year project was developing a spring-based energy recovery system for low speed running combined with a flywheel system for higher speeds. It will be interesting to see that combination on track next year.

Hydrogen or steam?

Birmingham’s loco, which had been almost silent due to its fuel cell, emerged from the loop sounding like a steam engine. The ‘chuff-chuff’ was, in fact, due to a failed motor. As there was no way to disengage it, it was getting worse all the time. A decision was taken to skip the energy recovery element as the running could cause further damage and to press on to the noise and traction tests. Even with the damage the loco was still very quiet and the team was hopeful of a good score.

Just one run was made up the hill and the team retired gracefully back to the station.

Much anticipated

So that left London Underground. Everyone wanted to see how the novel energy recovery system would perform.

The loco came around with half of its top cover removed. The commercial generator had a thermal cut-out installed and, in the confines of the metal body, it had been overheating. Taking the top off seemed like the best answer.

After going around the loop, the loco set off to do its energy recovery run. Stopping in front of the judges, pressure measurements were taken and the train released. Sixteen metres later, it slowed to a halt. Everyone was impressed!

But wait, the judges had recorded too high a pressure drop. Some extra stored energy had been used over and above that recovered in the braking run. The distance was disallowed. The team backed up to make another attempt.

This time, when the train stopped, it hadn’t recovered enough energy. Try again.

On the third attempt, caution reigned. Using less than the total stored pressure, a distance of just under 10 metres was recorded. It was a winning distance but, as points are allocated based on relative performance, the margin had been reduced.

And time was running out. Three attempts at energy recovery left time for only one hillclimb. It would have to count.

The start was faultless but would the missing engine cover affect the noise reading?

Towards the top of the hill, the thermal cut-out did its job and the train stopped. A mad dash from the driver to reset it and get it restarted did the trick, but time was ebbing away and the chance of a win in the Traction Challenge must have gone with it.

That brought the trials to a close. Every team had experienced mechanical trouble, some worse than others, and no-one knew who would win. London Underground had been impressive on energy recovery, but had stopped on the hillclimb and, they felt, blown the presentation. Birmingham had been unbeatable on noise but had missed out energy recovery. Interfleet had been generally reliable, but hadn’t impressed on energy recovery although at least they recorded a result for that test. It could be anyone’s contest.

So who won?

Teams, judges, officials and spectators gathered in the marquee by the station building to hear the result. IMechE President Mark Hunt, who had been at the event all day, thanked everyone for attending and for the competitors’ hard work. He also thanked Lady Gretton and the Friends of the Stapleford Miniature Railway for their hospitality in allowing the IMechE to stage the Railway Challenge at such a fine venue.

Then it was time for head judge Bill Reeve to announce the winners. He also thanked the teams, and commiserated with Sheffield, before saying how pleased he was that every entrant had won something.

The University of Birmingham had once again showed the way in green technology with their fuel cell and that had won them the Noise Challenge.

Despite suffering the “odd little frustration along the way”, the University of Huddersfield had worked extremely hard to recover from an in-service failure – something experienced by all full-scale railway engineers. If possible the judges would have awarded the team a special award for perseverance, but in any case they had won the Business Case Challenge.

Transport for London, appearing as London Underground, was the newcomer this year. While it was “worrying that London Underground couldn’t build a loco to fit a loading gauge”, the team had entered a novel energy recovery system. Mechanical systems seem to have the edge over electrical systems at low speed and it was no great surprise that the team had won the Energy Recovery Challenge. A little more of a surprise was that it had also won the Ride Comfort Challenge, and by a country mile.

Interfleet had been by far the most reliable entry. They still had problems, but had completed every challenge on time and were also winners of the Traction Challenge (despite the damp track).

It was all very close, but the overall winner, with all of the challenges and also a reducing score for reliability taken into account, was newcomer London Underground. Team captain Luke Foy thanked his colleagues, their employer and the IMechE. He also thanked Hydac for the accumulator technology that had been used for the energy recovery system.

Then it was time for photographs, to break down the locos and put them back in their vans, and to reflect on the weekend. A lot of work had been put in by all of the teams, including Sheffield, and the result had been some impressive engineering. Once again, a lack of testing had been evident and it does seem that all of the teams need to get started earlier for next year’s event so that they can all complete all of the tasks set for them.

Now we need to know what will change for next year’s regulations, and encourage a few more teams to take part in this excellent Railway Challenge.