Assembly in Action: Gear Products Aid Actuator Motion On New Mars Rover
February 23, 2010
Forest City Gear has supplied 60 space-qualified gear components, housings and carriers to Aeroflex in Hauppauge, NY, a major contractor on the newest Mars Rover for the Jet Propulsion Lab (JPL). Scheduled for launch in late 2011, the Mars Science Laboratory mission will determine whether Mars was or still might be capable of sustaining microbial life and, thus, be inhabitable.
Mars Rovers have been on the Red Planet since January 2004, sending back a nonstop data stream. The newest generation Rover, the Mars Science Laboratory, will be twice as long, four times the overall size and ten times the weight of the previous Rovers. It will be lowered to the surface of the planet by a tether mechanism, similar to a sky crane. (The tether mechanism will last approximately 7 seconds in the Martian atmosphere.) Forest City Gear supplied various spur, helical and spline gears for the Rover. The gears will be used for the vehicle’s drive gears, gearboxes, planetary gears and wheel assemblies.
Forest City Gear finished, hobbed and shaped the gears using dozens of cubic boron nitride grinding wheels made specifically for this project. The diameter of the gears ranged from less than 0.25 inch to 4.5 inches. The gears have fine surface finishes and a maximum pitch of 96. The gears were produced in lot sizes ranging from several pieces to 100 pieces.
Forest City made many of the gears from start to finish according to prints supplied by Aeroflex. For other components, Aeroflex outsourced the blanking to other vendors. Forest City then cut the gears or ground the blanks. Jared Lyford, production manager at Forest City, noted that, on many of the parts, the profile cornering and tip relief were particularly challenging, especially on some of the various alloy materials, where performance and weight factors also held top priority.
Of particular note is a three-tiered, internally geared carrier used in a drive assembly on the Rover. This component was machined from bar stock of an advanced engineered alloy that has properties similar to titanium, but is better able to hold the fine pitch and undercut gear design. This alloy remains stable during heat treating and behaves more predictably during precise machining and undercutting. The alloy actually shrinks, rather than expands, during heat treating.
“Our relationship began with a modest order from another vendor for some small gears on the first-generation Rover wheel drives,” says Fred Young, CEO of Forest City. “The shaping of the high crown design was a problem for the customer’s previous suppliers, who couldn’t get a cutter with enough back-off to successfully cut the crown shape. The crown hobbing had a shorter relief, and a different cycle was needed at the back edge.”
Confronted with this issue, Young suggested a design modification to accommodate the crown hobbing by shortening the spline face width, widening the relief groove voids, and acquiring a smaller-diameter hob than could be typically manufactured. These suggestions were quickly accepted by the customer, and parts were delivered in short order-with the added benefit of a weight reduction that translated into saving thousands of dollars per ounce on the final payload.
A similar situation arose on the second Rover’s gears. Aeroflex came to Forest City for a specification check on its gear supplier’s work. When Forest City’s quality department determined that the sample gears were out of tolerance, Aeroflex gave the company the order on the spot.
Because Aeroflex required 100 percent inspection on every dimension of every part, Forest City devised its own software programs to facilitate processing of the massive data files.
For more information on gear components, call 815-623-5242 or visit www.forestcitygear.com.