Hi all!

Roman wrote:

> 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)

This is worth to try!  Sounds like amnesty for TeamUR the Second.  It will
be saved for later.


>> 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.

I understand.  To move, the robot needs a support (good ol' Newton!) but the
friction is not everything. You must agree that after while of skidding the
robot should start moving but nearly it didn't.  It looks for me that there
is micro-acceleration and micro-deceleration of rotation of the stepper's
shaft (in my case: without gearing).  I think that even with the rubber
wheels this micro deceleration can be drastically decreased when the rubber
band stretches "on step" and releases the energy between steps. It makes the
whole movement smoother.  I tried it with the "shiny chain" and the rubber
band.  The band really makes a difference.


>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/

I saw The Ants.  Love them but look at this PIC bot:
http://chanhak.com.ne.kr/robot.html/


>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.

Yep!  As I wrote in response to Peter's feedback: I am already experimenting
with one purchased some time ago in my local hobby store: Hirec HS-55 servo
"it looks very promising. Dim. 7/8"x5/8"x3/8", very light comparing to the
currently used steppers, A LOT of torque: 18oz.in!."


>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.

What you are saying is that I should leave the electronics controlling the
servo and send the pulses?  This is a very good idea!  As I saw servo
hacking somewhere in the Internet I need to replace the potentiometer with
resistors to force continuous rotation.  But if I will stop pulsing the
servo should remain in the same position.  Is it true?


> 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.

Solar bugs...  I tried this approach on the very beginning.  I am not a big
fan of biocore. I am rather PIC-er.  Unfortunately looks for me that this
type of propelling tends to be somewhat unpredictable because of high
rotation speed of DC motor.  Besides I would like to give to my robots an
ability to climb some object since the are supposed to be desktop robots and
my desk is never empty :o)

Thanks for your time!  I am sure that I will run in some more problems soon
(with PIC for example) and it will be an opportunity to let you guys know
how is going.

Irek
http://teamur.netfirms.com

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