Let's Make Robots!

How to make a battery charger (Question)

Are there any "rules" when choosing a battery charger? Lets say I have a 5v supply with 500mA current. What should the charger specifications be?

Coaxial helis

I sorta got into "flying" robots recently and I have found answers concerning most of my questions, but there is a particular thing I don't understand about helicopters; how do the coaxial system work (I mean, how can I make one from scratch). I understand that each rotor cancels the other's torque, but how does all this mechanicaly work? Are the rotors dependant on each other for speed (I suppose that's not true because the heli turns probably by increasing torque generated by one rotor and decreasing torque on the other).

Anyone knows the HS-35D Micro Servo Motor?

This servo motor looks very nice and it's very small, but it costs a LOT. I think it would fit just fine in applications such as helicopters or quadcopters. 

HS-35D Micro Servo Motorhere it is: http://www.robotshop.com/ca/hitec-hs-35d-micro-servo-motor.html

Detecting laser beams?

Using an Arduino, I guess I would modulate (PWM) the laser module and have the photocell light sensor pick up the frequency. Would this work?


Servo time/speed and position control (using an Arduino)

Is there a way to control servo position and speed at the same time? ex: you want to build a biped but you don't want the movements to be jerky.


Interfacing two arduinos in the same robot

I'm wondering if I can make two arduinos interface with each other i.e. one for the servos and another one for sensor reading and receiving commands by RF (no need for tx-rx). Sorta like a master and slave thing. I would just want actually to make variables that both arduinos can read and write. Is it possible by hooking the tx rx pins together?


Momentary push button to on/off switch?

Is there some way to make an on/off switch using a momentary push button? I think the buttons feel more natural. They are smaller too. Just wonderin'...

Measuring voltage with an Arduino

I was wondering if I could measure battery voltage simply by hooking the battery's + to an analog Arduino pin so that my robot can know when it's low on power. From what i've understood, a battery of 1.5 volts is dead when it outputs 1.4 volts (gonna do some research about this). I guess I can apply this approximation to different voltages battery. The only problem is that, if I want to use a battery with voltage superior to 5v (Arduino analog pins set 5v as a maximum), how do I divide the voltage? Again, I guess I'll need op-amps to do that and voltage dividers, but what do I exactly do?

Using an RF receiver/transceiver pair along with a wireless camera to process the images and send commands to a mobile robot

I would like to create a setup I will be using for a lot of my upcoming robots. A small wireless camera that will be ultimately outputting through USB to my computer. The computer processes the video and sends commands to the robot via RF. I guess the serial connection will be no more than 1900 bds. How can I coordinate RF and image-processing in a single program for autonomous navigation/other tasks (I can almost hear GroG saying "MyRobotLab" ;)?