3D Printed DIYbio Magnetic Stirrer V2

This is version 2 of our 3D printed DIYbio magnetic stirrer. Our original design used an 80mm computer fan and 2 13x2.5 mm neodymium magnets hot-glued on (hot gluing magnets can demagnetize them, see here).

Improvements in version 2 include:

• larger platform;
• sturdier platform to hold more weight;
• 12V DC motor + motor controller for better speed control;
• easy to customize 3D printed magnet rotor;

The support structure bears weight on the platform, through the support structures down to 4 inner feet and onto whatever surface the stirrer is on. It can easily hold a 6L water container without the platform sagging which would otherwise cause the rotor to make contact with it and disrupt operation.

We've included the SketchUp file so you can modify parts like the case size, supports, motor mount, and the rotor in case you have a different motor you want to use or different sized rare earth magnets.

• 12V DC motor (27mm diameter, around 70mm in height);
• DC barrel adapter (female);
• 12V DC wall plug;
• motor speed controller;
• M3 10mm nuts/bolts (x20);
• jumper wires;
• neodymium magnets (13mm diameter x 2.5 height) (x6)

3D Printing

All the 3D printed files are available as a zip file here. But you can also view and download the files at Thingiverse here if you'd like.

Wiring

Wiring is very simple.

1. The positive and negative wires from the DC barrel adapter go to the positive and negative power screw terminals on the motor controller;
2. The positive and negative wires leading from the motor — connect to the positive and negative motor screw terminals on the motor controller and — that’s it.

Turning the knob all the way counter-clockwise turns off the power to the circuit acting like a power switch as well as a speed controller. Everything is covered in the video here.

Assembly: Magnetic Stirrer

1. There are spaces on the supports, controller mount, and the motor mount to fit in M3 nuts. If they just barely fit but you can't quite get them in, put the bolt through and as you tighten it, it will force the bolts into place. You can hot glue or friction weld (see our video tutorial on friction welding here) them in place;
2. Friction weld nuts into the leg posts of the cover;
3. Place the electronics into place, bolting the motor mount into place and then the support structures in place;
4. Press fit 6 magnets into the magnet rotor;
5. Press fit the rotor onto the shaft of the 12V DC motor. Open up the rotor's opening if needed if it is too tight. You can use a tiny dab of hot glue placed at the top of the shaft and push the rotor down in case it is too loose. Make sure it is pressed down several millimeters below the support structures or it will make contact with the stirrer's cover once fully assembled;
6. Use M3 x 10mm bolts to secure the inner and outer feet onto the bottom of the case. You can hot glue or friction weld them in place so when you remove the bolts to disassemble the stirrer you won't lose the feet;
7. when putting the outer feet in place and closing the cover, keep the knob close to but not sticking out of the opening in the case. Once the case is on and in place, pull the knob through and drive 2 more M3 x 10mm bolts into the holes in the bottom.

Assembly: Stir Bars

The stir bars are printed in 3 pieces; 2 covers and a middle section that you press fit the magnets into.

When the magnets are pressed into place, friction weld the top and bottom covers on. Check for gaps in your welding to make sure water can't get into your stir bars.

Operating the Magnetic Stirrer

!!!Safety!!! Exercise extreme caution when using electronics around liquids. Always fill and close your containers away from where your stirrer is located. Keep a cut-off switch or access to the wall plug convenient in case you need to immediate cut power. If you spill water, unplug everything and clean it up. Don't risk electrical shock!

1. Once everything is assembled, place a stir bar into a flat-bottomed glass or plastic container;
2. Secure a lid on top of the container;
3. Plug in the 12V power adapter in the back of the stirrer;
4. Turn the knob clockwise slowly to activate the motor and spin the rotor until you get the degress of spin you desire.

Applications

A magnetic stirrer is designed to allow long-duration hands-free stirring especially of a closed container. There are several applications you could use your stirrer for but keep in mind 3D printed stir bars are not food grade nor are they rated for high temperatures or corrosive chemicals.

• stirring hydroponic nutrient solution;
• mixing grated soap to produce a liquid soap;
• separating seeds (like tomato seeds) from pulp for seed harvesting;

This stirrer is designed to be highly versatile and easily modified by users with 3D design or electronic skills. Feel free to use this design as the basis of a better design. Just please make sure to share it!