Crash Testing

The University of Tulsa's Crash Reconstruction Research Consortium has developed a cable system that is capable of passively guiding vehicles into one another. The system is portable and can be taken to any venue, provided a few 3/4" holes can be drilled in the testing surface.

Crash tests require a day to prepare vehicles with a remote braking system and the cables. Once vehicle preparation is competed, another couple hours are required to make final preparations and adjustments. It takes an afternoon to take down and clean-up. Overall, a single crash test takes two whole days.

Crash Testing Kit

The TUCRRC crash testing kit was born from a Senior Design project from Wright State University by members of the mechanical engineering class of 2006. The customer for that project was Russell Strickland of the Fairfield Police Department. The advisor for the project was Jeremy Daily.

The goals of the project were to design a portable crash testing system that could safely crash two moving cars into each other at various angles.

The kit has undergone adjustments since 2006, but the original design has changed little.

The fundamental premise of the system is the tow cable is attached to the outside of the hubs using a frangible rope in a "Y" shape. As the vehicle drifts in one direction, the cable will pull on the outside hub and give some steering corrections. This action is performed automatically and results in the vehicle following the cable.

The following sections provide a brief description of the system we use. These are just ideas and the content contained in this document is for informational purposes only. Fitness of utility and safety cannot be guaranteed; therefore, it is not recommended that anyone create their own kit.

The vehicles are propelled and guided using the same system shown below. The hollow braided rope is fit over 5/16" steel cable. If the vehicle drifts one way, the rope will pull on the appropriate wheel and correct the trajectory. This enables a self guided system.

Wheel Plates and Axles

The wheel plates are cut from 3/8" plate steel. A trailer axle is welded to the center of the plate. A coupling nut is welded to normal lug nuts that are used to attach the wheel plates to the front axles. An anchor pin is used to attach the rope to the trailer axle.

The wheel plates are constructed using t pieces welded together. The base plate is a custom piece cut from 3/8" steel plate. Below is the technical drawing for the device.

A printable .pdf of the drawing is available here. The Solidworks 2011 part file is available here. This part can be CNC cut with a water jet, plasma cutter, laser, or CNC machined on a mill.

The second part is a trailer axle with tapered roller bearings and a hub. The use of the seals and lubrication is optional. They can be purchased at A&N Trailers in Tulsa, OK. The back side of the axle should be counter bored and tapped with a 1/2-13 thread. This enables the axle to be bolted to the plate. Then the back of the axle should be chamfered and welded to the plate. This will prevent the hub from coming off during a pull. Photographs of these axles follow. Each photo is linked to a high resolution image.

 

Lug Bolts and Extensions

Ordinary coupling nuts (1/2"-13) are welded to lug nuts. At least three lug extensions are needed per side. Lug sizes may be different, but the most common are the 12mm nuts. Some SUVs and pickups will use 14mm. A few European cars will use lug bolts. The coupling nuts can be purchased from McMaster-Carr, part number 90977A195. A jig to keep the coupling nuts lined up with the lug nuts during welding is useful, as shown in the following photograph.

Rope

Hollow braided rope is used after splicing loops in the ends to attach to the spindles. Each leg is about 12 ft long and must be the same length to prevent drift. An overhand knot is placed at the center to make the legs the same length. The front loop is attached to another hollow braided loop about the yoke rope. A steel cable is fed through the center of the hollow braided rope and the end is duct taped. The steel cable is 5/16" 7-19 galvanized.

Pulley (Sheaves)

A bronze bearing 3 1/2" block is used to guide the cable. These are rated for 1500# but should only be used once, due to the high speeds and dirty environment. The blocks are drilled into the ground and attached with concrete anchors as shown below.

Brakes

The fundamental safety system for the kit is a set of remote actuated air brakes. These brakes are powered with compressed air and actuated with a radio link controlling a pneumatic solenoid. A digital radio link proved to be much more reliable than an older analog radio.

The braking system has the following parts:

• Radio Controller: Spektrum DX5e DSMX 5-Channel Transmitter at Amazon
• 2 Spektrum Receivers (one for each car)
• 2 Receiver battery packs and chargers
• R/C Switch to convert throttle signal to on/off relay. TU-CRRC uses a Battleswitch from Dimension Engineering.
• Air Solenoid that takes the Battleswitch relay from the radio and opens an air valve. An example is the ASCO 8300 Series. The ones used by TU-CRRC were purchased on e-Bay.
• 12V source to power the air solenoid.
• A pneumatic cylinder with about 8" of travel and at least 4 square inches of area.
• A rod end joint and a steel bracket that can be screwed to the brake pedal.
• Various hose and pipe fittings.
• An air regulator.
• An air tank.

The air sources is mounted in the back seat. A radio controlled solenoid valve is used to apply air to the pneumatic cylinder.