Hello everybody! I am going to describe how I built a car which can move around, grab and pick up ping-pong balls (or any other small objects of similar size) with the help of a robotic arm and deposit them in a box/ enclosure.
Step 1: MATERIALS REQUIRED
- Four Plastic Boxes (1 for the car, 1 for the 1st rectifier, 1 for the car controller and the last one for the 2nd rectifier plus arm (& gripper) controller)
- Two General Purpose printed circuit boards (1 for each rectifier)
- The components required to build two full wave bridge rectifier circuits (i.e. two 12V/1A transformers, 8 1N4007 diodes, two 4K7 resistors, two 470µF/25V electrolytic capacitors and two LEDs (which will serve as indicators))
- A three pin plug and some wire for the mains supply.
- Three pairs of bolts and nuts (To fix the rectifiers to the box)
- Four DC Motors (I used 12V/1A, 60RPM DC motors with gearbox)
- Two tracked wheels (11 cm diameter) and one castor wheel
- Eight micro switches (with NO, NC and C terminals; NO: Normally Open, NC: Normally Closed, C: Common)
- 13 meters (approx. 40 Feet) twisted pair wire and two meters (approx. 6 Feet) of single-core wire (SWG 23 or 0.61 mm i.e. 0.024”) - one meter of one color and one meter of another color will help in differentiation.
- MECHANIX or any other mechanics kit for designing the arm & gripper.
- Suitable bolts of different sizes, with compatible nuts and washers, respectively.
- A small Aluminum (Aluminium (UK English)) piece 4 cm x 1 cm x 1 cm (I cut it from an old towel rack). This is to secure the arm properly to the motor shaft with bolts and nuts so as to prevent the arm from falling or moving in any random direction.
- Three Aluminum (or Aluminium (UK English)) C-channel pieces 4.5 cm (L) x 3.8 cm (W) x 1.9 cm (H). The size chosen was adequate for enabling fastening of the motor nuts, respectively, from the inside, and at the
same time, ensuring that the motor shaft of each motor was able to rotate in both directions without interference. Note that it is not necessary to use C-Channel pieces – one can use suitable steel brackets/ plates or even wood!
- One bolt (~1 cm diameter; length: ~10 cm), three washers and two nuts. This is for the counterweight.
And of course…..
Soldering Iron, Drill Machine (drilling to be done under guidance if one is not well-versed) and General tools i.e. screw drivers, spanners, files etc.
Step 2: Bridge Rectifiers
Assemble and solder both the full-wave bridge rectifiers on the respective P.C.Bs and connect them to the respective transformers. After checking that the circuits are working, drill a hole (of the size of the bolt you are using to attach the rectifier to the plastic box) on the PCBs and attach the PCBs to the plastic boxes, respectively. Similarly drill two more holes in each box to attach the transformers to the plastic boxes and attach them also. Connect them via the plug to the mains (separate plugs can also be used to power the bridge rectifiers, respectively, but I used a single plug and divided the mains supply for powering the bridge rectifiers).
Photograph shows the bridge rectifier for the Car Controller.
Step 3: Car Controller
For building the car controller, connect the NCs and the NOs (respectively) of the micro-switches 1, 2, 3 and 4. Now fix the four micro-switches i.e. 1, 2, 3 & 4 on the car controller box after drilling suitable sized holes. Solder two wires on the positive-positive terminal of the diode bridge and on the negative-negative terminal of the diode bridge respectively and connect them to the NO and NC of any one micro-switch (1/ 2/ 3/ 4). There is no specific polarity required. The photograph of the Car Controller and its circuit is given.
Step 4: Car
Take the plastic box for the Car (chassis) and drill two holes, on opposite faces of the box, having diameters equal to the inner diameter of the motor nut, taking care to align both the holes to ensure that the motor shafts are linearly aligned. Now insert the motor from inside the box and fix the motor nut from the outside of the box. Repeat this for the second motor. Affix the wheels on the motor shafts, respectively, and also affix the castor by drilling suitable holes on the other (far) end of the box.
Take two suitable lengths of a twisted-pair wire to ensure adequate range of movement of the car and positioning of the car controller box, respectively. Make two holes on the side of the Car (chassis) box and solder one end of the twisted pair wires as follows: Each wire of one twisted-pair wire to one terminal of the Left and Right motors, respectively, and each wire of the second twisted-pair wire to the second terminal of the Left and Right motors, respectively. Make two holes in the Car Controller Box and insert, respectively, the other ends of the two twisted pair wires, respectively. Then connect/solder the other end of the two twisted-pair wires (i.e. four wires), respectively, to the COMMON (C) terminal of the four micro-switches (1, 2, 3 and 4) in the Car-controller box. Switch on the supply and press the buttons. Your car should be working! Two micro-switches would control the clockwise motion of each motor while the remaining two micro-switches would control the anticlockwise rotation of each motor. Pressing both the switches controlling the clockwise rotation of the motors simultaneously would take the car forward while pressing the remaining two micro-switches would take the car backward. It would be useful to label the working of the motors on pressing the respective switches on the controller.
Step 5: Arm & Gripper
The arm and gripper are to be assembled with suitable components contained in a MECHANIX kit or any other similar mechanics kit, and attached rigidly to the car. In my case, it was necessary to add a counterweight to
counterbalance the weight of the gripper motor as the motor weighed ~225 grams. The counterweight was attached at such an angle so as to allow easy movement of the arm. More steel members were added on the side of the arm for strengthening so as to reduce sideways swaying of the arm while operating the car and/or the arm. In the gripper, semi-circular steel members were added to enable easy grabbing of the ball/ object. An additional steel member was added at the bottom to prevent the ball from falling. Two brackets were suitably fixed to the semicircular steel members so that they would push the ball inside the gripper.
Step 6: Arm (& Gripper) Controller
For building the Arm (& Gripper) controller, connect the NCs and the NOs (respectively) of the micro-switches 5, 6, 7 and 8. Now fix these four micro-switches on the Arm (& Gripper) controller box after drilling suitable sized holes. Solder two wires on the positive-positive terminal of the diode bridge and on the negative-negative terminal of the diode bridge, respectively, and connect them to the NO and NC of any one micro-switch (5/ 6/ 7/ 8). There is no specific polarity required.
Take two suitable lengths of a twisted-pair wire (having similar lengths as in Step 4 above) to ensure adequate range of movement of the car and positioning of the Arm (& Gripper) controller box, respectively. Make two additional holes on the side of the Car (chassis) box and solder one end of the twisted pair wires as follows:
Each wire of one twisted-pair wire to one terminal of the Arm and Gripper motors, respectively, and each wire of the second twisted-pair wire to the second terminal of the Arm and Gripper motors, respectively. Make two holes in the Arm (& Gripper) Controller Box and insert the other ends of the two twisted pair wires, respectively. Then connect/solder the other end of the two twisted-pair wires (i.e. four wires), respectively, to the COMMON (C) terminal of the four micro-switches (5, 6, 7 and 8) in the Car-controller box. Switch on the supply and press the buttons. The arm and gripper motors should work! Two micro-switches would control the up and down motion of the arm motor while the remaining two micro-switches would control the clockwise and anticlockwise movement of the gripper motor (i.e. to hold and release the object, respectively).