In this Instructable I demonstrate how to build a sample rotator using Erector set parts and littleBits. The sample rotator, or media rotator "is a common piece of standard laboratory equipment that is used for continuous mixing of lab samples, for example for slowly reacting or dissolving components" (1). I've broken the process of building the rotator into six steps. First, build the rotator base. Then build the support to prop up the rotator base. Next build what I call the "windmill," or the arms where the centrifuge tubes containing the samples are attached. I then demonstrate different methods for attaching the centrifuge tubes to the rotator and how to build the circuit to drive the littleBits motor module. Finally, I show the adjustable power supply wall-wart I use to power my littleBits projects.
Update: My littleBits sample rotator was featured on Dangerous Prototypes!
littleBits are color coded electronic modules that connect together magnetically to create simple electronic circuits. They are designed for ages 8 and up so hobbyists, designers, makers, and artists can add light, sound, and motion to their crafts and projects. Since they connect up magnetically (no need for circuit boards, breadboards, or solder), you canít accidentally connect them the wrong way. With littleBits you can quickly build electronic circuits in a matter of minutes.
The color coded modules are divided into four categories. Blue, for power, currently includes three modules-the power module to which you connect a 9 volt battery, a coin battery module, and a USB power module. Pink for "input," currently includes almost two dozen modules such as push buttons, switches, potentiometers, light sensors, and so on. Orange, for "wire," includes several wires, branching connectors, and logic gates. Finally, the green "output" components include a little over a dozen modules such as motors, a fan, a buzzer, several kinds of LEDs, and a speaker.
An example of a circuit might be the blue power module connected to a green motor module. Switch on the power switch located on the power module and the motor spins. (2)
(1) Source: http://www.teklalabs.org/sample-rotator
Step 1: Build the Rotator Base
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In the littleBits Base Kit, the motor module comes with an adapter for a Lego cross-axle so you can add motion to a Lego project. There does not seem to be a littleBits adapter as of this writing for other construction toys such as Kínex or Erector. I decide to see if I could use the littBits motor with Erector set parts to build a simple motorized project for your home laboratory.
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.
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. In the second picture you'll notice I included two set screws to mount the worm drive on the littleBits motor axle.
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
4 Large screws
4 Plastic collars (spacers)
10 Small screws
1 Standard hex wrench
1 set screw hex wrench
1 littBits motor module
1 littleBits wire module
Step 2: Build the Support to Prop Up the Base
4 Small screws
3 9-hole perforated strips
Step 3: Build the "Windmill"
1 Bush wheel
2 15-hole perforated strips
4 Small screws
Step 4: Attach the Centrifuge Tubes
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.
Step 5: Build the littleBits Circuit
1 littleBits battery and cable (1)
1 littleBits power module (2)
1 littleBits dimmer module (3)
1 littleBits bargraph module (4)
1 littleBits wire module (already attached to motor module in step 1) (5)
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.
Step 6: Adjustable Power Supply
You might have to leave your sample rotator running for quite some time and this will likely wear out the battery that came with the kit.
It is somewhat difficult to find the specifications on a 9 volt battery, but some sources suggest that a 9 volt battery can provide 200mA (milliamps) and others say 500mA of electric current but you canít always trust what you find on the internet. According to the schematic for the littBits power module there is a thermistor installed in the circuit which appears to limit the current to 500mA so, I have 9 volts and 300mA selected on the adjustable power supply.
The first module I tested was the motor with no load on it and the motor did spin up. The next circuit I built included the dimmer bit (potentiometer) and the bar graph bit.
The last three pictures show the circuit switched on and then increasing the power with the dimmer bit.
To conclude, I showed you how to build a sample rotator using Erector set parts and littleBits including the rotator base, the support to prop up the base, and the "windmill," or the arms where the centrifuge tubes containing the samples are attached. I demonstrated different methods for attaching the centrifuge tubes to the rotator and how to build the circuit to drive the littleBits motor module. Finally, I suggested an adjustable power supply wall-wart to power littleBits projects to save on having to buy more 9 volt batteries.
I've also built a magnetic stirrer out of littleBits and Erector set parts and posted the article on Science 2.0:
For more DIY projects please visit my column Square Root of Not on Science 2.0: