Introduction: Waving Robot

About: We are an international community that designs circuits from used components.

In this Instructable, you will be making a waving robot.

I constructed the circuit shown in the first photo. You can also implement this control system with MOSFETs. However, MOSFET transistors are hard to find in old electronic circuits. The link the to article about MOSFET motor driver on Hack a Day website is:


- pliers,

- wire stripper,

- screwdriver,

- soldering iron (optional),

- solder (optional).


You will need: 2 mm metal wire, 1 mm metal wire, a few screws (you will need 2), a few NPN BJT power transistors(you will need one), a few PNP BJT power transistors (you will need one), two heat sinks, heat sink transfer paste, small wheel, a short piece of high power wire, dc motor, wires, block of wood, matrix board, two 100 ohm power resistors, two 10 ohm power resistors, two 10 kohm resistors, two 470 uF electrolytic capacitors, one 100 uF bipolar capacitor, one 470 uF bipolar capacitor, electrical tape, two bolts, two washers and two nuts.

Step 1: Attach Transistors to Heat Sinks

The next step will explain how to choose transistors.

You put heat transfer paste onto the heat sink and attach the transistors with the screwdriver.

In the two photos shown, there are a total of four transistors. Two NPN attached for first heat sink and two PNP attached to the second heat sink.

Step 2: Make the Circuit

From the circuit, you can see how to choose the power transistors.

Maximum current: Vs / Rc2 = 3 V / 10 ohms = 300 mA

Maximum power occurs when Vce (collector emitter votlage) is half the supply voltage.

Maximum power dissipation: Vce * Icemax / Rc2 =1.5 V * (1.5 V / 10 ohms) = 225 mW (assuming the motor is short circuit)

Maximum collector-emitter voltage: 3 V

Maximum base current: (Vcin - Vd - Vbe) / Rb2 = (3 V - 0.7 V - 0.7V) = 1.6 V / 100 ohms = 16 mA

The resistors are used are recycled. Thus not the best choice for this circuit. The four diodes attached to the motor ensure that the motor will not damage the transistors, capacitors or power supply during discharge. You cannot forget that the motor is made form inductors that feed high current into the circuit after the power supply is off. After the power supply is switched off, the motor might spin due to inertia and generate power that will be fed back into the circuit thus damaging all components.

The circuits is connected to a square wave generator. You can realise a square wave generator with 555 timers. However, 555 timers is made to drive speakers not high current motors that this circuit allows.

I used 1000 uF for C1 and C2 but the robot you see on the video worked with a pair of 470 uF. 1000 uF will drain too much current from power supply and might explode. However, higher C1 and C2 resistors will keep the robotic arm spinning for longer during each cycle. Lower C1 and C2 resistors will cause the motor to turn off before the cycle ends.

I suggest that you set the power maximum supply current to low. There are high current power supplies and high current batteries out there that can really blow up the capacitors. I did not attach a 10-ohm resistor in series with power supply and circuit because my power already has 10-ohm internal resistance and the motor was not spinning fast enough.

The bipolar Cin capacitor looks like a normal electrolytic except that is can conduct current in both directions without failing. You need to try 100 uF and 470 uF to obtain the preferred response. I tested the circuit with an electrolytic capacitor because I did not have the bipolar.

If the motor is not spinning then try to double the square wave amplitude.

If the circuit is not working then try to double the square wave generator amplitude. Do not increase the supply voltage. The D1 and D2 diodes ensure that both transistors are off when V1 is at half supply voltage. Keep in mind that if you increase the amplitude then you need to check the maximum base current specifications.

Step 3: Attach Motor to Board

This motor was taken from an old video cassette recorder (VCR).

This is why you need a high power wire, for the plastic tube that you attach to the motor rotor as shown in the first video.

Step 4: Make the Arm

You use pliers to make the arm as shown.

You are now done.

Robotics Contest

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Robotics Contest