MRI is the most powerful diagnostic imaging modality available. The major drawbacks are cost and complexity, limiting its use mainly to industrialized countries and larger hospitals¹ . Multiple studies showed that there are several clinical applications where the diagnostic value gathered from low (B0=0.2T) field MRI is equivalent to costly “high” field (B0≥1.0T) systems^2-6. Cost effective open source imaging (COSI) is a collaborative initiative currently building an affordable low field open source MR scanner with the technical documentation freely available at www.opensourceimaging.org. As part of this initiative COSI Measure has been developed in order to automatically map the static magnetic field. COSI Measure is an open source multipurpose 3-axis system for ~3000€, which can be equipped with other field mapping probes like electromagnetic field sensors, used for 3D printing / CNC machinery application or other applications, that require precise programmable movement and sensor readouts in space and time.The mechanical subsystem has been designed with the free version of SketchUp (Trimble Navigation Ltd.) and is displayed in Figure 1. A strong and robust setup was intended, to support positioning the measurement system in safe distance to the magnetic field of an MRI, while being able to use sensor probes that cover the distance between the driver and the target. The base frame consists of (40x40)mm² aluminum profiles and has the dimensions of (800x800x800)mm³. Four ball screws have been used with a 5mm thread distance. Floating bearings have been used to support the mechanical movement. Ball screws and floated bearings are mounted on aluminum (10mm thickness) plates. Limit switch holders have been designed and 3D printed to control position of the sensors and to keep cabling distances short (Figure 2).The schematic of the COSI multipurpose system is displayed in Figure 2. The heart of COSI Measure is a Beagle Bone Black (BBB)with an 1GHz ARM cortex A-8 processor, 512MB DDR3 RAM and embedded Linux. In addition the BBB is equipped with 2x PRU 32-bit microcontrollers for real time control of the stepper motors. The BBB has 65 GPIO pins allowing for flexible application, HDMI and USB port for standalone application (monitor, keyboard, mouse) and an Ethernet port for remote communication. In addition to the BBB we used a BeBoPr++ and a J5-BOB. The BeBoPr++ is designed to work with the BBB, which can be mounted on top. It is equipped with interfaces to connect up to 5 motor drivers, 6 limit switches and thermos sensors for a possible CNC/3D-printing application. We used 4x NEMA23 stepper motors (3A@36V, 3NM holding torque, 1.8° per step at 200 steps per evolution) together with 4x DM542A motor drivers, which allow 2-128x microstepping leading to a theoretical precision limit of 200nm and half holding current operation for power saving. The motors and drivers are supplied by 2 AC/DC power modules (36V, 9.7A). Six inductive limit switches (4mm detection range) are used to detect the working range of COSI Measure. An emergency power off button has been included. Control of the system can be either performed over a GUI or G-Code. For magnetostatic field measurements a 3-axis Gaussmeter (460, Lakeshore) was used.The working volume of COSI measure is (50x50x60)mm³. It can be easily adjusted changing the dimensions of the aluminum profiles and ball screws. In order to measure backlash and precision, a ball pen was attached to the probe holder (Figure 1). The system supports submillimeter movement as shown in Figure 4a-b with no visible backlash (Figure 4b). The submillimeter vibrations are due to duct tape fixation of the ball pen, which can be conveniently addressed with a customized probe holder. The current maximum speed of the system is 0.4m/s is more than sufficient for field mapping applications. The limiting factors for the speed are the mechanical motor couplers connecting the stepper motors to the ball screws, which will be exchanged for future applications since the electronic subsystem supports much higher. Furthermore the motors and current system are strong enough to easily lift >3kg, which is more than sufficient for field probes. The maximum strength is yet to be determined after the motor couplers have been exchanged. COSI Measure is a programmable multipurpose 3-axis robotic system, which can be utilized for magnetostatic field measurements, electromagnetic field measurements, 3D printing, CNC machinery and various other applications, that require reproducible submillimeter movement and/or measurements. Design files, software, technical documentation, part list etc. will be made available according to the values of open source hardware at www.opensourceimaging.org.