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Innovations Lead to Improved Small-Vehicle Simulation

MTS senior engineer Dave Fricke discusses new simulation technology that controls both rider loads and chassis motion to improve the accuracy of motorcycle and ATV testing.

Q: What testing challenge prompted MTS to pursue new technologies?

When considering the requirements for small vehicle structural testing, it is important to factor in the effect that the rider has on the vehicle. The rider can be both a source of load input as well as load reaction for the vehicle. Obviously, a rider’s physical influence on the vehicle will increase as a vehicle size decreases. This influence also is magnified in harsh operating environments, such as those encountered during off-road riding or motocross racing, as riders intentionally use their body masses to control vehicle movement.

Motorcycle, scooter and ATV test engineers have always been looking for ways to accurately reproduce the effect of the rider at the handlebars, seat and foot-pegs. These loads can be vital in evaluating how the vehicle will perform during real-world conditions. Up until now, however, test labs have had to depend on “passive” rider systems for simulation. These have consisted of humanoid dummies, or other mechanical configurations of springs, masses and dampers. These passive systems can be “tuned” to reproduce specific rider loading and damping effects, but cannot provide a general solution for all riding conditions, and would probably do more harm than good if strapped onto a motorcycle during an extreme event.

Another part of the challenge was caused by the physics of the extreme events themselves. On the track, an event like a motocross jump and landing might require eight or 10 meters of vertical motion. In the laboratory, we need to duplicate these events in less than a half-meter of vertical motion. Somehow we had to “shrink” these extreme riding events to make them fit within the practical limitations of simulation system design.

MTS has a long history of innovation in this area. Advanced control methods have been developed that can compress the time it takes to duplicate an event, which shifts the frequency of the motion and consequently reduces the motion required. MTS’s “long stroke” vehicle simulators, which have the most motion capacity for structural simulation in the world, still require techniques like this to simulate large events like slalom maneuvers.

“Jump” simulation is a different challenge, however. Although the vehicle’s wheels are used to generate and absorb launch and landing loads, it is gravity acting on the entire vehicle chassis that returns it back onto the track. To get the reduced chassis motion required without using the suspension to pull it back into position, the chassis motion needed to be controlled directly.

Q: What solution has MTS developed?

The active rider/restraint design team, led by Paul Carroll, engineered an innovative actuator mechanism that attaches directly to the motorcycle or ATV. The fixture allows rider loads to be introduced into the chassis, yet can also be used as required to restrain and position the chassis in order to simulate extreme off-road maneuvers. Blending the system control requirements to get the best combination of rider loads and modified chassis motion was my responsibility.

Vertical foot-peg loads are applied from below the vehicle, and handlebar loads are applied at an optimized angle via an adjustable H-frame assembly. On the track, instrumented components are strain-gauged to measure the handlebar and foot-peg loads. We then use RPC® (Remote Parameter Control) software to reproduce these forces in the laboratory via the active rider mechanism. For motorcycle applications, the control system also applies differential foot-peg forces to hold the vehicle in an upright position. The current design also makes it possible to add or substitute a seat input as well. Even though a rider can be seated at times on a motocross course, the foot-pegs and handlebars see the most significant loading during the large impact events.

The foot-peg attachments actually serve a dual role. Along with a forward vertical chassis attachment, they are also used as the attachments for the active restraint system. When simulating a jump event, the normal simulation control will begin to require vehicle motion that exceeds the physical capacity of the simulator. We’ve developed a control method that anticipates this, and switches control of the foot-peg and front vertical inputs from “rider” mode to “restraint” mode.

For example, when simulating the vehicle launch, the restraint system will become active, and use low-frequency loads at the attachments to catch, carry and pull the chassis into the correct position. To duplicate landing loads, the system will then switch back to controlling the rider forces on the foot-pegs. The idea is to have the restraint system active only when required and only at low frequencies. Most of the time, and at higher frequencies, just rider loads are generated.

Q: How will vehicle test labs benefit from applying active rider/restraint technology?

: For off-road vehicles, jumps are some of the most damaging events a vehicle will ever see. The addition of the active rider/restraint to a simulator can significantly improve the accuracy of jump simulation. Even for less severe simulation, test engineers have been struggling with the limitations of passive rider dynamics. Unfortunately, a human is not passive; he is constantly changing the way he couples and decouples his mass to the vehicle chassis, and oftentimes two different riders will load a vehicle very differently, even for the same sequence of events on the test track. The active rider technology allows the test engineer to simulate both riders without physically changing the simulated rider mechanism, as would have been done with previous passive solutions.

In general, lab simulation aids understanding of complex component loading and chassis dynamics. For extreme events such as a motocross jump, it can be a huge benefit when compared to dangerous, expensive and non-repeatable tests on a track or race course. Now, thanks to the new active rider/restraint technology, motorcycle and ATV manufacturers can realize the same benefits of laboratory simulation that the automotive industry has enjoyed for years.


MTS Systems

14000 Technology Drive
Eden Prairie, MN USA

Tel: 952.937.4000
Tel: 800.328.2255
Fax: 952.937.4515
Email: info@mts.com