Drill-powered Centrifuge

This instructable will teach you how to build a high performance centrifuge based on the use of a commercial drill modified with a 3D printed part. This project was made by Olivier Dalstein and myself, it is our first instructable and we hope that it will be useful to you!

Centrifugation has many applications ranging from the cleaning of water to lab work, either in biology (blood centrifugation) and chemistry (settling of a suspension). However, for an efficient separation high speed centrifuges (> 5000 rotation per minute) are needed, which are a costly equipment (around 2000 €) that require a considerable investment. Drills cost less than 100 €, plus you may already have one at home. If not, you can always ask to your handyman dad/grandad.

By looking around in the instructables database we saw that similar prototypes of centrifuge based on the use of a Dremel already existed, but we decided to post this one anyways for a few reasons : 1) we believe that our setup is more suited for larger volume of water as a drill can hold larger structures than a Dremel 2) Drills are a more common tool than Dremels and 3) we propose an experiment to get an accurate measurement of the rotation speed based on the use of a photodiode controlled by an arduino.

To build the centrifuge you will need the following parts and supplies.

• 1 drill

• 3D printed PLA structure

• 1 bolt

• 1 nut

• Plastic Centrifugation falcon tubes (15 ml)

• (Optional) Wood boards to building a stable station

The falcon tubes were the only part we didn’t have, we bought five 15 ml centrifugation tubes for one euro on Aliexpress.

The structure was printed from a Ultimaker 3D printer using PLA as material. The model was made with the free software Sketchup Make, the attached file .stl correspond to our final prototype. Note that the schemes are made to be used for falcon tubes of 15 ml and the structure should be modified if tubes with a different diameter are used. The structure has 5 holes in the middle part to be more versatile on how you want to connect it to your drill. If you don’t have a 3D printer yourself, you can use a 3D printing service.

The assembly of the centrifuge is fairly easy. The 3D printed structure can be attached to the metallic part using a screw with a nut. Doubling the nuts on the screws prevents the untighting of a nut due to the vibrations. After that, the screw is simply attached to the drill as a broach, using the tightening system of the drill. If the nut untighten when you spin the drill, you are spinning in the wrong direction.

In the videos and photos shown in the other steps we used a custom-made metal piece that we had lying around along with 4 screws and 8 nuts. However, this is not necessary and only 1 screw with 1 nut can be used as long as the screw is not too small.

At this point it is already possible to centrifugate using equilibrated tubes (same mass). However, it is not very convenient as the drill needs to be maintained in position by the user. In order to get a more stable setup, a station was built with wooden boards. This section will not be detailed as it would only be relevant for drills that have the same size as the one we used. Basically we placed the drill in the desired position and attached three pieces of wood (two on the sides, one on the back) using screws to maintain the drill in the desired position. The drill start button is left accessible on the front side. The setup in use can be seen on the first video of this article.

To demonstrate the capabilities of the centrifuge, we separated pollutants (chalk and small dirt particles) from water. The tubes were centifugated at maximum speed (see next step) for 5 minutes. After centrifugation the water is clear (left), showing that the separation of the suspended solids was successful.

To measure the rotation speed of the centrifuge, we used a photodiode connected to an arduino. There are plenty of tutorials for basic signal collection using arduinos available on instructables if you are interested. In this setup a light source (smartphone) is placed above the structure and the photodiode is placed below. In order to get only one peak of current for each full rotation of the centrifuge, 3 of the 4 holes were covered with aluminum foil. Note that to get a constant current from the photodiode, you must use a light source powered by a continuous current (smartphone, flashlight or anything powered by a battery) and not by alternative current (lamps connected to an electrical plug).

At maximum speed the period between two current peaks is 6.5 ms, which correspond to an average of 154 rotations per second or 9200 rotations per minute. This is a high speed similar to the speed of laboratory grade centrifuges.