Very Computer

We are building a mobile robot and are planning to use the HC11evbu and
stepper motors. We need a light 12V rechargeable power supply. I was told
there are batteries that are lighter and more powerful than lead-acid, but
can't find any in the cataloges I have.

 If anyone knows of a better kind of battery and where I can find one I
would greatly appreciate it.

  thanks

     Steppers are inefficient; they draw current even when stationary.
If your main wheel drive motors are steppers, your power consumption
will be excessive.  You need servomotors.

     There's much to be said for lead-acid batteries: cheap, reliable,
easy to charge and discharge, good power density per unit volume.  
NiCd battery packs for model cars are the next step up.  The more
* battery technologies start to get expensive and require
elaborate charge/discharge control.

                                        John Nagle

Depending on what your budget and weight restrictions are, why not look at
the batteries for cordless power tools. 12V NiCad are common and aren't that
heavy (I don't have a scale so I can't tell you exactly). After that I would
look at laptop batteries. 12V NiMH are the standard, with Lithium Ion being
the best overall, but at the highest price.
My advice would be find someone with a cordless drill and ask to borrow it.

Good luck.

<Steppers are inefficient; they draw current even when stationary.>

John,

Steppers do not of necessity draw current when they are stationary.  They have
residual
holding torque when unpowered.  For more holding torque, then partial voltage
is applied to them.  A good stepper driver will permit you to specify the
degree of holding torque.

I submit that an unpowered servo, unless driving through a worm gear, will have
less holding torque than will an unpowered stepper.

No free lunch here!

Bob / Romar