In a previous article I built a magnetic stirrer using littleBits and Erector set parts for the home laboratory. At the end of the article I added a design for a sample rotator (a device used to continuously mix lab samples). I have (somewhat) improved the design of the Erector set and littleBits sample rotator and in this article I document the build.

The Rotator ”Base”

The sample rotator uses a worm drive. I didn't need to change the gear ratio--the motor module is built for torque, not speed. But I was hesitant to mount the rotator mechanism directly onto the littleBits motor axle. Perhaps the axle could take the weight of up to four 50 ml centrifuge tubes. The gear box on the motor module, however, has dainty little gears that remind me of the gears in an analog watch so I was concerned whether these gears could withstand the stresses of such a load.

Parts needed:

4 3 by 5 hole flat plates

2 3 by 5 hole flat plates

Note: The yellow Erector base plates are flimsy, so I had to reinforce them with the two silver Steel Tec 3 by 5 hole flat plates. The holes on the Steel Tec plates are larger in diameter and don't line up well with Erector parts. The yellow plates simply serve to line up the holes properly.

1 5 by 7 hole base plate

2 3 by 5 hole base plates

1 3 by 5 by 3 hole double angle strip

2 Angle brackets

1 Worm gear (with 2 set screws)

1 Pinion gear

1 Axle

4 Large screws

4 Plastic collars (spacers)

10 Small screws

10 Nuts

1 Standard hex wrench

1 set screw hex wrench

1 littBits motor module

1 littleBits wire module

The diameter of the littleBits motor module axle is smaller than an Erector set axle so you may need to use two set screws to center the axle of the motor module. Pictured above you'll notice I included two set screws to mount the worm drive on the littleBits motor axle.

Support to Prop Up the Base

Parts needed:

4 Small screws

4 Nuts

3 9-hole perforated strips

The Rotator

Parts needed:

1 Bush wheel

2 15-hole perforated strips

4 Small screws

4 Nuts

6 washers

To attach the centrifuge tubes to the "windmill" blades I decided to show several different examples. Screw clamps seemed to me to be the most effective method to hold the centrifuge tubes on the rotator, but you can use any number of fasteners such as rubber bands, zip ties, or what have you. The black strap that holds the 50ml centrifuge tube on the rotator is a re-sized Velcro cable-tie from a laptop power cable.

Build the littleBits Circuit

Parts needed:

1 littleBits battery and cable 

1 littleBits power module 

1 littleBits dimmer module 

1 littleBits bargraph module 

Connect the battery and cable to the power module. Next connect the dimmer module to the power module. Then connect the bargraph module to the dimmer module. Finally, connect the wire module to the bargraph module and the motor module.

Switch the circuit on. Adjust the dimmer module until you see all five LEDs light up--this will represent full speed for the sample rotator.

You might have to leave your sample rotator running for quite some time and this will likely wear out the 9 volt battery. I suggest using an adjustable power supply wall wart like I demonstrated in my littleBits magnetic stirrer article.