Let's Make Robots!

ganging servos together

I am in the design phase of building a robot arm roughly 40 cm long that can pick up several pounds ( 1 kg for easy math).  To get a 40 kg-cm torque servo is a pretty expensive servo ($60 at pololu.com although anywhere else anyone knows something cheaper, please share!). 

Has anyone ever tried to gang several servos of the same brand and type together to work in concert?  I was going to put a balancing weight on the far end which will help, but still calls for a pretty expensive servo (30 kg-cm)

Ultrasonic HC-SR04 library for AtMega 8 (ie Dagu Mini Driver)

Does anyone know of a library that will work with a Dagu Mini Driver (Arduino NG AtMega 8) and an HC-SR04?  At first I thought I must have two sensors that are dead, but when I hook them up to an Arduino they work fine.

I tried our friend Google, but none of the ultrasonic libraries list if they are backwards compatible to the AtMega 8.  I tried two different libraries and neither seems to work.  I tried different pins, still no joy.

Thanks in advance,





motor driver suggestions - 6v 6a stall

I am looking for suggestions on how best to drive my Pololulu motors on my MopBot.  This bot is basically a swiffer mop attached to the bot which it pushes around so it requires more torque than the usual small bot I have done before.  These motors are rated 450 ma @6v with no load and 6 A stall.  I am using 6 NiMH AA batteries in series for about 7.2V - 7.5V although could go higher if needed.

sanity check please...


The problem I am trying to solve is I want to create an IR beacon that can be used with IR detectors on my robot so it can zero in on my charging station when the batteries are starting to go. 

My question is how to wire up multiple leds in a circuit.  I googled and found a formula on instructables.com but it comes up with a very low resistor value which I just don't trust.  I have a 9V wall wart which puts out about 10V with no load.  I have 3 IR leds which are rated 1.6V forward voltage and can pull a continuous 100 mA.

Robot water level sensor idea


I spend 2 - 2.5 hours each day commuting to and from work, and I have plenty of time to think about things. 

One thing I have been thinking about is that I have never seen anyone use liquid as a way to keep a robot level.  I can't imagine that I am the only one to think of this; people must have looked into it and discarded it as a solution, or we would have three of these on our workbenches right now.  Or am I onto something really, truly original?