414 Mars 2020 Specific Requirements  

There are several key and d riving requirements derived from the Mars environment and mission  requirements :   1. The mission objective to look for compounds that provide evidence of life on Mars levied strict  Contamination Control and Planetary Protection handling , design,  and assembly constraints ,  including:  reducing organic materials used for assembl y and treating them to minimize outgassing  and deposition on crucial components, cleaning  all surfaces to prevent contamination from  migrating due to handling, and eliminating/reducing viable compounds from spores and organic  materials from Earth.   2. The actuators located on the extremities of the rover arm are subjected to wide diurnal  temperature  changes , which is highly stressing on electronic components and bonded materials.   3. In addition to pyrotechnic release devices, the rotary percussive drill generates an environment that  can be defined as a combination of a random vibration, sine vibration, and pyroshock. This  environment varies depend ing on several factors , including the hardness of the rock being drilled  into, the percussion frequency used for drilling, and the weight -on-bit applied.  Ref. [7] contains   more information on the coring drill . The dynamic environment fatigues  components and can  amplify natural modes in hardware, which then couples  with fatigue induced from extreme ther mal  cycling.  

maxon Catalog Flat Motor and Gearbox Design  

maxon has 50 years of experience designing and manufacturing brushed and brushless DC electric motors,  gearboxes (both planetary and spur), feedback devices , and control electronics. The brushless DC motors  are offered in several families of types, covering both ironless winding and iron- core winding types. The  iron-core winding types are in turn divided into external and internal rotor  families where the rotor mounted  permanent magnets are respecti vely outside or inside the windings. Both the M20 and M32 motors are  derived from maxon’s “flat motor” family  (Figure 3) ,  which are of the BLDC external rotor  type.  

For industrial applications, compared to other BLDC  types, the flat motors represent a simple, low -cost  design that delivers high torque in a short (but large  diameter) envelope. When operated without a  housing in Earth atmosphere conditions, the  exposed spinning outer rotor also enables excellent  convective cooling and hence high continuous  power ratings.  

maxon’s flat motor family covers various diameters (14, 20, 32, 45, 60 , and 90 mm), all of which share the  same basic design. A large -diameter rotor provides the structural support and acts as a magnet return for  a ring magnet. This rotor is supported by two ball bearings housed in a flange/bearing support structure.  The bearings are preloaded by use of a spring. A stator sheet stack is  wrapped with magnet wire and  mounted to the bearing support structure whil e being electrically connected to a printed circuit board (PCB) ,  which  also holds three Hall sensors  that detect the main magnet position.  

maxon has the industrial heritage for the flat motor  design, which  has been built several  million times,  including over 1 million units for commercial truck exhaust gas cleaning systems , an application that   provides real world proof of the robustness of the basic design.  

Flight Fidelity Modifications to the Catalog Designs  

It was known from previous maxon work that commercial motor designs usually require some modifications  to allow reliable operation in a Martian environment , in particular , the wide temperature range cycling,  Figure 3. maxon flat motor standard features