2D Clinostat for Simulated Microgravity Experiments

Ground-based microgravity simulators, such as rotating 2D clinostats, are valuable tools for studying gravity-related processes. This work presents a versatile, g-value-adjustable 2D clinostat designed to hold a single 90 mm Petri dish.

The drive unit is an SM-28BYJ-48-5V stepper motor coupled to an external 12/44 gear set. The 28BYJ-48 is a 5-wire, 4-phase unipolar stepper motor operating at 5 V. It includes an internal gearbox with a 64:1 reduction ratio. Stepper motors are controlled by electrical input pulses, so the rotational speed is proportional to the pulse rate. In full-step mode, this motor rotates 11.25° per step (or 5.625° in half-step mode). The minimum step angle is therefore 5.625°/64. With the two external gears, one full rotation of the wheel corresponds to approximately 7,500 steps. Consequently, the rotating wheel can operate at a speed of 0–10 rpm.

The motor is controlled by an Arduino via a ULN2003 driver module. The ULN2003 module is bolted to the back of the tilting part of the clinostat, above the motor.

A clinostat is used to reduce the directional effect of gravity on biological samples by continuously rotating them, thereby averaging the gravity vector over time. Although the magnitude of gravity remains 1 g, the constantly changing orientation can prevent organisms and cells from establishing a stable “down” direction, which helps to suppress gravity-driven phenomena such as gravitropism and sedimentation—provided that the rotation is sufficiently fast relative to the response time of the investigated process.

Clinostats are therefore widely applied in plant physiology, cell biology, and microbiology as ground-based microgravity simulators, and they are often used to pre-screen experimental setups before conducting spaceflight experiments. At the same time, results should be interpreted with care, because rotation can introduce side effects such as residual centrifugal acceleration, fluid motion, and shear stress, especially in liquid-containing vessels like Petri dishes.

This clinostat was built for amateur experiments. I used it to germinate garden cress (Lepidium sativum) plants.