Building the low gravity simulator presented a unique challenge in the importance of symmetry and dynamic movement. We ran into slight issues when 3D printed parts were slightly asymmetrical, causing imperfect revolution building mechanical stress into the structure. We included bearings and slip rings to counteract wire tangling and ensuring smooth rotation.
Build Process
Background
In order to simulate the conditions of reduced gravity for our cyanobacterial growth experiments, the team began developing a Random Positioning Machine (RPM). An RPM is a ground-based research tool designed to approximate microgravity by constantly reorienting a sample around multiple axes, thereby canceling out the effect of a single, constant gravity vector. Unlike clinostats, which only rotate around one axis, RPMs use two independent axes of rotation, allowing for a more uniform simulation of weightlessness. This makes them especially valuable for testing biological systems intended for space applications, such as bioreactors for life support or construction on Mars.
The goal of our design process was to create a compact, low-cost RPM that could house a bioreactor vessel while still being adaptable to our team’s experimental needs. The initial step in this process was to design a system that mirrored prior research examples, particularly the low-gravity bioreactor presented in this paper: [1] . By using this as a reference, we ensured that our concept aligned with established design principles while leaving room for modification to suit our project constraints.
Below is a picture of the preliminary idea for the RPM machine:
As this was still in early development, the model was made to very closely resemble the low gravity bioreactor found in this paper: [1] . However, as development started moving forward, it became necessary to design the bioreactor to fit the teams specific needs (such as our media, budget, manufacturing method, choice of hardware). The attachments on the side of the vessel were each made to hold an unique, necessary component of the bioreactor ( such as a sparger and battery pack ). As a result, the second draft CAD was developed:
A video of the model working in order to visualize the location of the motors:
Building for validation
However, although the intention of this model was to meet the needs of the team and research question to the best of our ability, there were still some oversights that were eventually resolved with the final draft of our model. The first of such oversights included the issue of creating a low gravity environment. In order for an RPM to simulate low gravity, there must be a symmetrical application of force in order for the gravity vector to cancel and thereby induce the low gravity environment [1] . Therefore, we removed many of the attachments that were attached to the vessel in order to prevent such asymmetric geometry from occurring. In addition, a plan was made to use a counter weight to prevent a bias in the gravitational vector due to the motor on the top of the vessel. Furthermore, another key oversight was bought up by UBC Physics and Astronomy’s Technical Services Director Mladen Bumbulovic who suggested that we use a smaller vessel which would aid the accuracy of the validation methods later on. In addition, an aerated bottle was used in exchange for a vessel made up of 3D print as not only would that remove the need for a sparger, but it would also allow for better autoclavability and ease of use of the dry lab team ( as they are familiar with the bottle ). Finally, a tray for electrical and bigger hole for bearings were made, and the product was split into smaller parts in order to fit onto the 3D printing bed. In order to prevent circuit elements from twisting from the low gravity bioreactors rotation, we used a slip ring to connect electrical components housed on top of the vessel. Below is the our final draft CAD before product:
Physical Assembly:
After finalizing the CAD design, the team proceeded with the physical assembly of the RPM. The 3D-printed components were produced in modular sections and then carefully aligned to ensure that the rotational axes remained balanced and perpendicular. Hot glue was applied onto rough, sanded 3D surfaces for better adhesion. Silicone sealant was also used as an adhesive. Slip ring wires were soldered onto the matching wires as shown in the circuit diagram below.
Photographs of the low-gravity bioreactor
Circuit Diagram
The circuit for both NEMA 17 stepper motors was assembled initially assembled using this circuit diagram:
This circuit diagram has been found to work with one stepper motor and one driver, however, this circuit had a lot of heating issues and is only suitable for low torque, low current and short-term run times. This circuit contains the Arduino microcontroller we used, DRV 8825 motor driver, stepper motors, and 12 V power adapter. However, upon implementing this, our motors were having difficulty spinning, which led us to modify the circuit by adding a capacitor of 100 μF into the circuit to regulate voltage fluctuations:
This circuit diagram is the same as the previous, just with a capacitor in parallel with the 12 V voltage source from the wall. Upon doing so, we were able to successfully spin the two motors in the circuit without interruptions and heating issues, which may arise when doing long runs or not using heat sinks on the drivers.
1. Ellena G, Fahrion J, Gupta S, Dussap CG, Mazzoli A, Leys N, et al. Development and implementation of a simulated microgravity setup for edible cyanobacteria. npj Microgravity [Internet]. 2024 Oct 25 [cited 2025 Oct 1];10(1):99. Available from: https://www.nature.com/articles/s41526-024-00436-x
