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Pneumatic BMX Gates Go to the Beijing Olympics
Joseph Ogando, Senior Editor -- Design News, April 29, 2007
When BMX racing makes its Olympic debut at the 2008 Summer Games in Beijing, the riders will kick off each race through a patented pneumatic starting gate. Thanks to its advanced electronic controls, this Pro-Gate design has set a new repeatability standard for the Olympics and any other BMX competition sanctioned by the International Cycling Union (UCI).
The elite riders who will pass through the new gate may not devote much thought to the response times and kinematics of pneumatic systems, but they are acutely aware of which systems are the most consistent. “The start is obviously one of the most important parts of a BMX race. If the gate performance varies even a little bit, the riders notice and complain,” says Johan Lindstrom, BMX coordinator for the UCI.
Before BMX racing earned its spot in the Olympics, variability was actually the norm in starting equipment. Lindstrom explains that local tracks have a wide variety of gates and “voice boxes,” the electronic controls that deliver ready-set-go commands and light signals to the riders before tripping the gate. For world championship races, the UCI had in recent years adopted a widely used electronic control system from Cartessa Corp. But the physical design of the gates and their pneumatic systems continued to vary from track to track. “Most of the gates looked like they had been put together by individuals working in their basements,” Lindstrom says.
Everything changed once BMX made the Olympics. “In the Olympics, there can’t be any question marks. There is a lot more pressure to develop standardized equipment,” Lindstrom says. “And with standardization, we saw we had an opportunity to improve the gates.”
That’s where Pierce Barker III comes in. His company, ProStuff, had been making single-rider BMX practice gates and multi-rider gates for BMX tracks for the past four years. Last year, he began working on the gate that Lindstrom ultimately chose for the Beijing Olympics. Like the earlier gates, the new Olympic model is built mostly from a collection of standard Parker Hannifin components — including pneumatic rams, FRLs, exhaust valves, hoses, connectors, industrial shock absorbers and aluminum profiles for some of the gate and accumulator structures. "They're all good, reliable components," says Barker.
Yet what's most interesting about the gate isn't so much the componentry as ProStuff's design philosophy. Barker has a day job as vice-president of Barker Rockford, a systems integrator that has been building industrial and military machines for about 50 years. "We approached BMX gates the same way we would approach any machine-building project — with a focus on safety, performance and reliability," he says. And that machine-builder's mentality has resulted in gate designs that are arguably the most advanced in the world.
Safe Gate
One of the things that immediately struck Barker when he first started looking at traditional BMX gates is just how inherently unsafe some of them were. He explains that the largest starting gates — competition models with space for eight riders — can weigh between 200 and 600 lbs. Typically driven by 4-inch pneumatic cylinders, these heavy steel gates rotate downward at rates up to 920 deg/second, he says. Yet even with all that heavy metal moving so fast, previous gate designs had little or no deceleration control. "The gates drop 90 degrees and just bang into the ground," Barker says. BMX races really do start with a bang, ones that can be louder than 100 dB.
All that banging has some scary safety implications. "Imagine getting a hand or foot caught under one of these gates," Barker says, adding that bad starts do sometimes put inexperienced riders in the trajectory of the falling gates. One such miss-start, for example, involves an over-eager rider going over the top of the gate just prior to it dropping, creating a pinch hazard. "A lot of what we saw out in the field when we began to develop our Pro-Gate products just didn't cut it from a machine safety standpoint' he says. “We didn’t want to design anything that was going to get someone in trouble later.”
Lindstrom agrees that safety was a top concern when choosing a gate design — but not so much the safety of the elite riders who will use the gate at the Olympics. “They’re professional riders who know enough to avoid the gate, but it’s a concern for young, inexperienced riders,” Lindstrom says, noting that children now start racing at six years old.
Barker enhanced gate safety in a couple of ways. First, he reduced the weight of the gates, by making them from aluminum. Less weight, in turn, allowed him to downsize the pneumatics and, consequently, the amount of energy needed throughout the gate cycle. "Less energy in means there's less energy to control at the bottom of the cycle," Barker says. ProStuff's Olympic gate uses a 4-inch cylinder running at 80 psi — far less than the 135 psi commonly used with heavier gates. ProStuff’s smaller gates require only 2-1/2-inch cylinders running at 40 psi.
Whatever energy is left at the bottom of the cycle, ProStuff takes care of with an adjustable cushioning mechanism. The last 5/8-inches of rod travel on the Parker air cylinders, which corresponds to roughly the last 3 degrees of gate rotation, can be cushioned by compressing exhaust air in the cylinder's rod end through the use of cushion valves. On its heavier models, like the eight-up version to be used in Beijing, ProStuff supplements the cushioning with industrial shock absorbers. Its practice gates and multi-rider models with individual gates rely solely on the cushioning.
ProStuff also developed proprietary control software to modulate the gate's double-coil DC solenoid valves as they first accelerate the gate and then switch over to the cushioning mode. "We control the amount of energy needed at any given moment to accelerate and decelerate the gate," Barker says.
Barker had another kind of safety in mind when he developed the Pro-Gate — electrical safety. Most of the models he noticed in the field run on 110 volts. “You’d go to a track and see the gate connected to the power supply by an extension cord,” Barker says. Even ignoring the potential hazard created by extension cord in frequently-wet outdoor environments, there’s another problem: “People trip on the cords and disconnect the power,” Barker says. “On other systems, if you lose power the gate drops. It happens all the time when people least expect it.”
The Pro-Gate, by contrast, runs on just 12 volts DC, which was possible in part because of its scaled-down pneumatic requirements. Barker also uses locking power-cord connections to prevent accidental disconnection. And most importantly, the double-coil solenoids on the Pro-Gate require power for movement in either direction. “If you cut the power, all motion stops, which is as it should be from a safety standpoint,” Barker says.
The safety provisions don’t stop there. Barker has also developed break-away hinges for some of his gate models. And one of his favorite demonstrations is to close a Pro-Gate gate on his hand. “Try that with another gate and you’d lose that hand,” he says.
Consistency and Reliability
As Lindstrom pointed out, though, safety isn’t the thing that most worries Olympic BMX athletes. They care more about gates whose cycle times don’t vary — whether from track-to-track or from race-to-race. According to Lindstrom, the UCI has met those concerns with a new repeatability standard that requires the gates to fall 90 degrees in 310 milliseconds with a cycle time variation no more than +/- 7 percent.
And for an idea of how finely tuned the athletes are to small variations, remember that BMX riders are professional athletes who won’t get far without quick reflexes. When Lindstrom first started developing the 310 millisecond gate-fall spec, he found that riders could easily pick up on variations greater 10 percent. “Ten percent seemed to be a breaking point in what people would notice,” he says. The UCI decided to drop the spec to seven percent to be sure that even a particularly observant rider would not notice any variability.
The UCI actually designed its spec around the capabilities of the Pro-Gate, according to Lindstrom. “It’s a super-consistent gate,” he says. How consistent? Barker says the gates consistently perform better than that spec and typically vary by less than 10 milliseconds versus 60 milliseconds or more for previous gate designs. Barker attributes the consistency to both the mechanical design of the gate itself and to the electronic controls, which use DC electronics. “AC is faster, but DC is more consistent,” he says.
Besides the improved safety and performance, the Pro-Gates’ controlled deceleration feature had offered a couple of side benefits. One is noise reduction. Barker says his gates produce from 70 to 80 dB of noise, versus the 100 or more from bang-on-the-ground models.
And the gates are proving to be reliable, according to Lindstrom. At the 2006 UCI Worlds in Sao Paolo, the gates went through 3,970 drops without breaking down or malfunctioning. That would be unusual for a steel gate. “Over time they work harden, become brittle and fracture like glass,” Barker says. “I’ve seen contests where the repair welder is on the starting line as often as the riders.”
