Let's Make Robots!

Accelerometer.. Which to buy?

I wanna get an accelerometer for my bot.

Inverse kinematics

Been trying to understand inverse kinematics for programming my quadruped Crap-Crab. I started out by reading Wikipedia's version, which lost me completely (WTF?). But then I found the explanation by this guy and it turns out, as I thought to begin with, that it's simply a matter of applied trigonometry.

Here is exactly what I need in a nutshell:

Servo problems!

I'm having a lot of problems with the servos I'm using to build a quadruped robot. I should start by mentioning that I bought the servos from Dagu like 4 years ago, BUT most of them had never even been unpacked until recently.

The problems are the following:

Homemade digital compass

Some time ago OddBot posted this circuit for a homemade digital compass based on hall effect sensors:

Compass_Schematic.jpg

Unfortunately CircuitBurn couldn't make it work. However I'm inclined to try again. A cheap DIY compass would be great.

So if anyone has ANY idea as to how this could be achieved let's hear it. It could be an improvement on OddBot's circuits or something completely different and wacky :D

Hooking up a Schmitt trigger (74HC14)

I need to hook up a 74HC14 to clean the signal from a QRB1134 IR sensor. I think I know how but I need to make sure. Could it really be this simple:

*Connect pin 14 to 5V (from Arduino)

*Connect pin 7 to ground

*Connect pin 1 to the signal output of the QRB1134

*Connect pin 2 to the Arduino analog in

*Place a .1uF cap between the 5V and the ground wire

Here is the datasheet and an example I used:

www.robotokulu.com/ROBOTOKULU_dosyalar/74HC14.pdf

TLC5940 anyone?

Allthough these chips are actually called LED drivers they are apparently capable of controlling servos...up to 16 of them :) There is even an Arduino library available for doing so. Pretty cool stuff. But I was wondering if anyone has any experiences with this? If yes then I'd like to know more about it. If not well then consider this a tip to keep in mind the next time you run out of servo pins ;)

NiCad vs NiMH batteries

I wanna buy a charger and some batteries so I've been doing a bit of research on the different types. However the information I found is somewhat confusing and outright contradictory. And in any case I'd like to hear about the experiences you guys have had using NiHM and/or NiCad batteries...

Which would be the better choice? Pros and cons?

Advice on accelerometers

Some questions about accerometers:

1) Which would be a good buy? I am putting together an order at seeedstudio cause they seem to have all the stuff I need at good prices. I'm thinking of throwing in this accelerometer, but I don't know if it's any good? I also saw that polulo has this cheaper model. So which would be the better buy? Or perhaps a 3rd option?

Cheap mini wireless cameras

I was playing around with some code for machine vision (object/facial/color/motion-detection) a long time ago, and I'm thinking to put a camera on a robot sooner or later and see where that'll take me.

So I was looking for cheap wireless cameras and I was astonished to find these:

900MHz Mini Wireless Color Camera w/Built-in Microphone - $25.50

Multiple swithces to analog input?

Just had an idea. I'm planning to use a LOT of (tactile) switches on a walking robot. For instance I wanna put several under each foot. But it seems like a waste of pins to use a digital pin for each switch (or use multiplexers). So I thought I might be able to connect the switches in paralel and read several at a time from an analog input using resistors of different sizes connected in serial with each switch. Like this:

switches_s.jpg