Son's robotics project

[Dewman]

My 8th grade son has to build a robot with another student and are allowed to spend $50 each.  I think the school provides the motors., but byond that I'm not sure.  The robot has to flip a verticle switch, a horizontal switch and move a golf ball into a hole.  I found out he doesn't have a clue and is behind.  Are there any web sites or other information available which I can access to help him?  Thanks!

[waltr]

A good start is read the "Robot Tutorials" found under this pages title above.
Lots of good starter info.
Then come back and ask specific questions.

[Dewman]

I'm still reading the tutorials (very informative) and I've figured out that this is a simple project.  It is a wired robot (both dc power and controller) so it should not be difficult.  The robot has to move around, flip light switches (both vertically and horizontally), and push a golf ball into a hole.  The school supplies the motors, so my son and his buddy need the rest and it has to be under $100.  The two motors on the robot I understand.  I don't know whether I need a complicated controller to make the robot move.  I've seen some diagrams, but I'm still working out the differential controller.  I guess they're available to buy.  The switches can be moved using servos, I guess.  Do I need a computer board to control these things or not?

[newInRobotics]

If robot can be controlled by a wired handheld gamepad, then microcontroller is not required as robot does not make any decisions by itself. To keep it simple and cheep all You need is 4 Push Buttons and two motors. This gives You differential drive without speed control and without compensator for different motor speeds (because 2 identical motors have slightly different speeds, meaning that your bot will drift to one side or another).

To compensate for motor speed difference You can add pot in series with each motor and adjust them so that both motor spin at the same rpm and bot does not drift to one side or another.

To get speed control You can add dual pot in series with Your motors. Now You can adjust directions with 4 pushbuttons and speed with dual pot.

For anything more fancy than this You will have to use microcontroller. Using uC gives ability to control bot speed using PWM (speed controll without loosing torque), compensate for drift (different motors speed) using shaft encoder. Also, uC allows You to control servos very easily. As nice as it is - it does require programming knowledge.

Good luck.

[Dewman]

I've seen an article about using an old atari joystick to control the differential controller.  I think all I need is one servo or other device for flipping one of the switches and just using the robot itself to turn the switch from side to side.  My real problem now is figuring out the differential controller for the drive train.  Is this something I need to build or can I buy one.  If I have to build it, is it fairly simple to do and does anyone have a design?

[newInRobotics]

I've seen an article about using an old atari joystick to control the differential controller.

You can't just plug it to the motor or microcontroller and expect it to work. To interface such a device with a chip You must write communication protocol defining how one will understand another. It will be much easier to create Your own "gamepad" using one potentiometer (read by Analog-to-digital port of microcontroller) to control speed and another potentiometer to control steering.

My real problem now is figuring out the differential controller for the drive train.  Is this something I need to build or can I buy one.

Setup in my previous post gives You differential motor control. If You want to control servo, You will have to use either 555 timer circuit, or microcontroller. In case You decide to use microcontroller, You will also need motor driver circuit (to spin Your wheels), which You can buy, or build in a form of 2 H-bridges (8 MOSFETs(4x P-channel, 4x N-channel)).

If I have to build it, is it fairly simple to do and does anyone have a design?

You can start looking for design by using Google or PROGRAMMING - DIFFERENTIAL DRIVE tutorial.

[Soeren]

Hi,

My real problem now [...]
Is this something I need to [...]
If I have to [...]

Forgive me for saying, but this really sound like you have completely taken over your sons homework and forgotten him in the process, perhaps out of interest, but I really don't think you're doing him a favor, as you're sparing/blocking him from learning.

If it's out of pure interest, why not make a family competition, where you both build 'bots and have daily/weekly discussions on the topic, exchanging ideas as well.