I've been working on the AFRON $10 Robot Design Challenge in between a massive garage reorganization project and installing fuel injection on my vintage Jeep Grand Wagoneer.
spring mousetrap instead of a DC motor.
What about a boat of some type? Or some kind of solenoid powered scooter thingy? There's opportunity to add some physics lessons to the robot this way, sure.
On the other hand, I'm concerned about the practicality of each approach. A simple tabletop wheeled robot seems most conducive to teaching programming and basic electronics.
I found a source for really inexpensive robot parts. Yes, from China. In the unlikely event that they arrive before the deadline, they represent quite a cost savings in the design without sacrificing functionality.
|See ebay seller ce10wy among others|
I've found hobby DC motors for well under $1 but a geartrain is hard to put together and can be costly. Using a motor to drive a large wheel directly is probably best in that case.
I spent a lot of time thinking of ways to develop actuators for steering or environment manipulation but none are cheaper than, as well as superior to, a $3 micro servo.
It seems I'm turning this into a shopping exercise more than anything else.
|Tower Pro SG90 9g servo, $3|
An ATmega328P costs just about $3 from Digi-Key, yet an ATmega168 or ATmega8 cost more. Cheaper options exist that are less Arduino-compatible, and some that are totally incompatible.
I've spent quite a bit of time on motor control. There are a few small ICs that can drive low voltage motors from low voltage power supplies (2 x AA). A cheaper option is a MOSFET h-bridge, but finding the right MOSFETs has been a significant challenge.
As for sensors, discrete infrared LEDs and phototransistors seem cheapest. My Microrobot uses these and I recall they worked reasonably well for basic obstacle avoidance, but I've not used them for line following.
I'm pretty confident I can make a functional, decent, mainstream line follower for $20 or less. Bulk discounts will definitely help get the price pretty low.
I don't expect to win the competition at this point. I'm sure others will come up with truly brilliant, creative designs leaving me slapping my forehead in dismay.
Still, I'll consider my efforts a success if I can come up with a useful design that can be used to teach kids.