Machine Design

A measured response to spec checks

The IndyRacing League (IRL) rule book stipulates maximum and minimum heights for certain parts of the race car in reference to other components as well as to the ground.

An IRL IndyCar on the Tech Pad

In the past, such measurements were made by hand, referenced from a flat plane placed against the bottom of the car. This method brought a host of problems. For example, the car could rest at an arbitrary plane with reference to the ground, or a car configured for an oval track would have left and right-side tires of different diameters. Besides the tires, cars designed for oval tracks are built with a certain pitch.

IRL, recognizing the problems, contracted with several consulting firms including Pi Research, Indianapolis (, a motorsport-electronics designer and manufacturer. The goal: Carry out electronic design necessary to meet specific rulebook measurement requirements. The companies, working together, designed an automatic XYZ positioning system to provide necessary measurements within 2 min.

Known as the IRL Tech Pad, the automated system now qualifies entrants at all IRL races. It incorporates six range-finding lasers from Pi Research to establish a reference plane for each critical measurement. The lasers measure the car underbelly, creating X and Y coordinates. System software, written in C++, uses a proprietary form of averaging to calculate a transformation matrix that maps the flat reference plane. The matrix then adjusts vertical, lateral, and longitudinal vectors to orient to the reference plane. From here, newly measured points are corrected to the adjusted vectors. Resulting are true, accurate spec measurements.

Pi Research turned to Maxon Precision Motors USA, Burlingame, Calif.(, for Tech Pad motors and controls. The Tech Pad positioning system rests in a steel and aluminum structure that incorporates ball-screw technology. Maxon's 32-mm, 80-W brushless motor drives the X axis while the company's 45-mm, 250-W motor drives the Y. Each motor features a three-channel line driver encoder for position feedback. Additionally, two45-mm motors drive the two laser-loaded axes. The Maxon motors and controls provide XY positioning accuracy for the laser heads to within ±5 microns (including mechanical backlash). The lasers themselves measure the Z axis, and are accurate to within ±50 microns.

Maxon's MIP50 controller runs the entire positioning system, offering PID position control and PI current control. The controller interfaces using an RS-485 port, allowing multiple units to be multidropped in a parallel configuration. The units are configurable for dc brush or brushless motors.

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