# Coupled System of Dual-Axis Clinostat and Helmholtz Cage for Simulated Microgravity Experiments
## 2 Design and Construction
### Mechanical Components of the Clinostat  
In the construction process, we strictly applied the postulate to limit ferromagnetic material as much as possible. Timing gears, pulleys, construction connectors for the clinostat frames, and the other cultivation parts are made of poly (lactic acid) (PLA) or polyethylene terephthalate glycol (PETG) filaments using 3D-printing technology. The cultivation sphere is made from polyester, and its parts are connected with screws and bolts made of nylon.  
The mechanical part of the clinostat consists of the static mechanical housing and the cultivation area. The frames are made of typical V-SLOT-type aluminum profiles. The metal parts were cut and formed with the use of a milling machine, and the assumed accuracy is below 0.1 mm. The \"plastic\" parts were printed using a 3D printer with 0.2 mm accuracy. The angular uncertainty of perpendicularly mounted parts is below one angular degree. We do not test what might be the maximum deformation for a heavy load. In recent experiments, we used a payload with a mass of about 1 kg and did not notice any significant deformation effects in the whole construction. The cultivation chamber was adopted from a commercially available geographical globe. The rotating alumina frame is driven by two-timing gears and one belt (cf. Figure 1--the motor mounted at the back vertical edge). To pass rotation from the second stepper motor to the sphere, a two-timing belt mechanism was used. The rotating frame axle is mechanically independent from the sphere axle, whereby it can rotate at its own speed and can change orientation. The gearbox is kinked at a right angle and the belt is guided with idler pulleys to power sphere rotations. Each timing belt has its independent tensioning mechanism. The axles are made of aluminum pipes in which water pipes and electrical cables are embedded. The water supply system is made of a peristaltic pump (DP-DIY type, 12 VDC, efficiency of 5-10 mL/min, made by INTLAB(Seri Kembangan, Malaysia)), polyurethane tubes of internal diameter equal to 2 mm, rotational connectors, and perforated silicon tubes located close to the cultivation area. A peristaltic pump prevents reversing water flow. To reduce angular velocity fluctuations resulting from uneven weight distribution, additional counterweights were used--for example, to balance the LED lighting system.  
The cultivation process has to be protected from external light sources to keep it controlled. The sphere has a diameter of 320 mm (Figure 3) and is divided into two semi-spheres to allow access and enable the preparation of seeds, cleaning, and harvesting. Inside the sphere, there is a plastic cylindrical basket with a radius of 95 mm, located symmetrically at the main cross-section, which is the base for cultivation. Directly attached to the plastic sphere, a second (apart from the main computer mounted to the main frame--cf. Figure 1) small, single-board computer of the Raspberry Pi type is used to acquire data from sensors. The clinostat stepper motors (Nema 24 manufactured by Nanote(r)) have 4 Nm torque. Each motor is driven by a DM556 stepper motor driver manufactured by Leadshine(r). The total size of the clinostat fits a volume of 620 mm width and length, respectively, and a 963 mm height.  
In addition to the clinostat, a static copy--the reference device--was constructed. It is used to compare results from the zero-mean-gravity experiment to normal-Earth-gravity circumstances. Figure 4 shows the static version.