Irek Rybark wrote:
>
> Yeah!
> Roman, thanks for the professional feedback.  I was hoping that there will
> be someone with *robotic* experience.

It's only professional if you pay! ;o)

> Ok. Then dreams about attaching stepper directly to the sprocket are really
> unreal?
> With the gearing the whole thing becomes too big for me.  I was thinking
> about building a robot with the dimensions below 1". The robots currently
> have ca. 2" and in the next generation should shrink rather than grow... :o)

Your motors had tiny metal cogs, if you find a larger
plastic gear that matches, and glue it to wheels with
rubber tyres you may get 3:1 or 4:1, and have tyres.
simple and still small, maybe smaller than the chain
setup you have now. The extra torque from re-gearing
makes all the difference. :o)


> Now I am aware that one of the problems is this "hard shiny chain" I was so
> proud of.  Mechanically there is no way to have this chain *not skidding* on
> the floor. There is no mechanical part, which can accumulate step's energy
> and smoothly release it.  Probably a drive made with pulleys and rubber band
> should help a lot. What do you think?

Not really. Part of the problem is the acceleration
and deceleration of the bot, when stopping and starting.
You *really* need rubber if you want decent traction,
unless the whole bot runs on a rubber tabletop.

> > My little stepperbot here:
> > http://www.romanblack.com/deskbot.htm
>
> This is a real beauty! :o) Especially impressive for me is that your robot
> "has enough torque to push a full coffee cup without slowing, in fact it
> will push about 1kg across a smooth table".

Yep it's quite torquey, the 7:1 gearing and heavy
bot weight make it like a little tractor. But again,
without the rubber tyres (only plastic wheels) it
won't push nothin'.

It really sounds like you want to make these bots
small, the best advice is to look at what the REAL
experts are doing, like the "ants";
http://www.ai.mit.edu/projects/ants/

For tiny bots you can get tiny "RC servos" which
have a motor and gearbox built in. They can be modded
to give continuous rotation. Try the RC (radio control)
web sites. Rubber wheels are a must. :o) You can also
add a tiny infrared sensor to the gearboxes, giving
you position feedback to the PIC at 32 pulses per wheel
rotation etc. Little servos are going to use 10x less
power than steppers, are smoother, more torque, etc etc.

One way that appeals to me is the "angled motor direct
drive" concept. You use tiny pager motors, with a tiny
rubber wheel not much bigger than the shaft, say 2mm shaft
and 4mm rubber "wheel" like a rubber grommet around the
motor shaft itself.

The gearing is provided mainly by the tiny size of the
wheel. The 2 motors are angled at about 45 degrees to
give some ground clearance. This gives decent start
torque and good speeds too. The secret is to put a
tiny IR encoder wheel on the back end of the motor,
and use good PWM control of motor voltage, giving
good slow speeds, good high speeds, good traction, good
energy efficiency, good positional feedback etc etc.
See the basic motor configuration of the Beam photovore;
http://www.robotbooks.com/beam_solar_robot_kits.htm
and improve it with a couple of optical encoder wheels
from a mouse. :o)
-Roman

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