411 Mars 2020 maxon  Commercial Motor Development from Commercial -Off-the-Shelf   to Flight -Qualified Motors, Gearbox es, and Detent Brake s: Overcoming Issues  and Lessons Learned 

Michael LoSchiavo*, Robin Phillips**, Rebecca Mikhaylov * and Lynn Braunschweig**  

Abstract  

Building on previous collaborations, maxon and the Jet Propulsion Laboratory ( JPL) established a  partnership to modify Ø20- mm & Ø32- mm Commerc ial-Off-The-Shelf (COTS) BrushL ess Direct Current  (BLDC) flat motors and a Ø22- mm planetary gearbox.  The commercial design was modified to meet the  requirements for  the Mars  2020 rover, a Class B  [1] interplanetary mission operating in the Martian surface  environment , while maintain ing as much of the industrial heritage as possible . Numerous i ssues   encountered during development were successfully addressed, and qualification of the design and  acceptance testing for the 10 F light Model (FM) actuators installed on the Mars  2020 rover was completed  on time for the rover assembly schedule.  

Mars 2020 Overview and Previous Missions  

maxon brushed motors have significant flight heritage on JPL Mars missions . The Mars Pathfinder  Sojourner rover contained 11 brushed direct current ( DC) motors based on the RE16 d esign  [2]. The Mars  Exploration Rover s (MER ), Spirit and Opportunity , each utilized 39 maxon brushed DC motors, based on  modified commercial “RE” series designs. At the end of the Opportunity rover’s mission , all of the drive  wheel motors were still functioning, having survived 5111 Sols (Martian day/night thermal cycles) , with  each  motor complet ing ~9 × 107 revolutions . Spare MER motors (4×  RE20 and 5× RE25) were also used as part  of the Phoenix lander. m axon has continued to develop brushed motors for the Martian applications Interior  Exploration using Seismic Investigations, Geodesy and Heat Transport  (Insight ) mission and ExoMars   mission  by modifying newer commercial designs , however , these designs were  not viable options for Mars  2020 due to the brush sensitivity to a pyroshock environment.  

Mars 2020 is the first step in a potential multimission approach to a Mars Sample Return mission and future  human exploration of Mars [ 3,4]. The primary objectiv e of the Mars Science Laboratory (MSL) and its  Curiosity  rover  is to search for habitablity . Mars 2020 [5] and its Perseverance rover  will seek signs of past  life and  collect Martian cores for  possible  later collection and return to Earth. The Mars 2020 project  maximize d the use of build- to-print hardware to reduce development risk and much of the project utilizes a  large amount of spare MSL hardware (specifically the cruise and descent stages) . Mars 2020 also levied  design constraints to remain within the MSL footprint in terms of mass, volume , and power on major  components , such as the rover chassis, which houses the Sample Caching System  (SCS) , and large robotic  arm.  

The SCS is one of the most advanced robotic systems ever developed for planetary exploration, pushing  more robotic Degrees of F reedom (DOFs) into a smaller volume than has previously been achieved. Within  the SCS, the Adaptive Caching Assembly (ACA) and Coring Drill  [6,7,8,9,10] requires  complex  mechanisms that need gearmotors smaller in volume than any equivalent hardware developed for MSL.  Additionally, solenoid brake channels in the motor controller were traded for additional sensor channels,  which required any new motors to utilize a passive holding torque mechanism. Tasked with Mars 2020’s  mission objective to drill, capture,  and store core samples along with volume constraints from the MSL 

* Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA   ** maxon international ag,  Sachseln,  Switzerland  

Proceedings of the 45th Aerospace Mechanisms Symposium, NASA Johnson Space Center , 2020