African Robotics Network (AFRON)

The AFRON "10 Dollar Robot" Design Challenge

Submission by Dave McIntyre

  1. Proposal – and base cost
  2. The device is in category 1, (tethered) and is intended to work exclusively with a Raspberry PI.
    My robot is a facial expression device. It consists of eyes and lips which move under the control of a Raspberry Pi. It has a microphone to listen for commands so it should be possible for example to train it using speech recognition software on the Pi and an appropriate use of the GPIO pins to for example “eyes right” or smile.
    It is intended to be hand built by the end user, having said that, many of the parts could be more easily and cheaply “factory built”.
    The cost is estimated to be approx. $6 for all the necessary parts. If the Raspberry Pi is not connected to a monitor with sound, a small speaker could be added within the remaining budget.
  3. Educational Application
  4. The aim is that by studying expressions and how they are built up together with the use of language to control the device skills will be developed in both the use of existing software and development of the control sequences which should readily generate positive outcomes (“eyes right” for example would be a very simple control sequence).
  5. Parts

  6. These are formed on a drinking straw former and consist of winding approx. 5m of fine enamelled copper wire (I recovered mine from a defective mains charger) onto approx. 2cm of tube. The cores are metal paperclips bent to shape. ($1)
    Eyes – cardboard disks
    Mouth – neoprene ‘O’ ring ($1) – I used a piece from an old seal making a look with a dab of superglue
    Boards – card
    Electronics, each solenoid requires a driver as the current needs to be approx. 100mA With a smoothing capacitor in place, the Pi should be able to provide sufficient current as the solenoids are activated only for short pulses. So, for each channel – NPN transistor (BC108), two limiting resistors and reverse diode across coil. (could be replaced with array of drivers chip). The whole assembly can be glued to the solenoids. ($2)
    Microphone insert with preamp with wire to connect mic to Pi (and plug). ($1)
    To assemble some glue will be required. Hot melt is very effective.
    Misc – card – glue -solder ($1)
    Estimated total $6.
  7. Tools
  8. Knife/Scissors to cut card ($3)
    Soldering iron ($15)
    Optional (electric drill or hand brace to speed up winding coils) $40
  9. Step-by-step instructions for creating your robot
  10. Wind the solenoids.
    Cut the card shapes and glue into place. Glue in solenoids. Solder drivers on. Split ribbon cable from Pi GPIO and take cores to drivers
    Plug microphone into Pi
  11. Mass manufacture
  12. I do not anticipate a cost saving, but manufacture of solenoids/actuators and punching boards from plasticard would create a more reliable product.
  13. Software
  14. None written.
  15. Tests undertaken
  16. I discovered this too late, but have tested the concept of using the hand made “drinking straw and paperclip” solenoid to move the position of a card “eye” and soft neoprene lip. It needs some work to refine the optimum number of turns and it may be improved by finding a suitable slightly smaller ridged tubing material.
  17. Pictures of your robot – none at present
  18. Videos of your robot in action– none at present


The concept could be extended by adding light sensors which would allow the eyes to be programmed to “look” to the light. This could probably be included within the $10 budget. Outwith the budget, a webcam would allow software to be written to attempt to copy facial expressions.

Drawings - hand sketches

Eyes solenoids
Eyes top view
Eyes front view
Lips solenoids
Lips top view
Lips front view