eVOLVER Forum

Would full fan spin speed be okay (for bacteria)?

A spill damaged one of the fans on our eVOLVER and we are working on getting a trained replacement but in the interim, we have replaced it with a standard fan from the manufacturer and moved the 3D printed magnet chassis into the new one. This fan will only spin at full speed, but I have tentatively and surprisingly found that the OD measurements and calibrations are less noisy compared to many of the other sleeves, and the turbidostat growth rate is higher and has a tight range (see Vial 9 on the bar plot below). For the time being, we have no need for variable spin speed. Unlike the other PWM controlled components which simply have voltage values ranging up to the maximum of 4095, it is not clear to me how the numbers sent to the Arduino for the fan translate into power management. but I am also not very familiar with Arduino code. . Since our OD calibrations and measurements are precise (I have not assayed accuracy as of writing), I was wondering if there was a way to get the trained fans to operate at full power the same way or if this would require placing standard manufacturers fans into the sleeves and if there was any reason to not do this with our bacterial cells, especially given that this full speed likely also discourages biofilm formation somewhat.

When you say full speed, do you mean that the fans are spinning as if you are applying 12VDC from an external power supply? Applying a constant 12VDC for long periods of time runs the risk of the magnets coming detached from the fan head. The arduino code is actually applying 12VDC (0 value for the Tlc PWM chip) for just a few milliseconds at a time. The number value sent to the arduino effects this for loop, the bigger the number, the longer the fan will receive power before being shut off. If you are using an external supply, I would recommend supplying a lower voltage.

I’m not sure what you really mean by “trained”. We eventually plan to use fans with a tachometer and PID control to achieve higher precision stir rates, but we aren’t doing anything special with the fans in the current setup beyond attaching the magnets.

The only other issue I can think of is if the vortex from stirring protrudes down low enough to effect the OD measurements, so as long as this isn’t happening you should be fine. With a standard culture volume around 30ml I don’t think this is likely.

You can easily provide higher stir rates within custom_script.py - you could experiment with values to find something that is closer to what you want. If you want to enable higher stir rates within the GUI, you could modify this variable. Do this at your own risk though, we have the max set to a typical range that we know works well and have not extensively tested faster rates for longer periods of time. Like I said, you don’t want the magnets to detach from the fans. As long as you don’t hear any buzzing or intense noise it’s probably ok.