Hi Irek, shame about the jerky problem. You really
need more gearing, like a 1:5 pair of gears, as you
probably won't get the performance you want with 1:1
connecting the stepper to the chain, even with your
small cog.

Steppers *will* vibrate quite a bit, and even with the
right gearing you might find that because you have hard
shiny chains it will still not get precise location on
the ground. It is fairly important to have good gripping
rubber between the stepper motor and the ground. :o)
My little stepperbot here:
http://www.romanblack.com/deskbot.htm
has 1:7 gearing on the steppers, and rubber tyres.
Without the rubber tyres it slides and does not drive
in a straight line or get accurate distance etc.
Even with the rubber tyres it loses/gains 1mm in every
50 or so, without rubber tyres it is more like 20mm
error out of every 50!! Skid city.

Another thing to think about is the h-bridges, they are
normally 3v to 4v (saturation) when turned on, so you
may only be getting 4v on your motor and losing 4v on
the bridge. Better to use 4 fets and drive the motor
unipolar (has half the coil resistance and 10x less
loss on the drivers).

You can get tiny stepper motors in any 3.5inch floppy
drives, dead drives are available everywhere. The best
advice I can give is a redesign using at least 5:1
gearing, *rubber* tyres, and low saturation drivers.
:o)
-Roman


Irek Rybark wrote:
> The second robot [TeamUR the Second] was supposed to be a [my!]
> technological breakthrough because I decided to go for the stepper motors.
> I was hoping for more precise motor control.  The first stepper motor
> control attempts were very promising.  Since I am electronics engineer it
> was easier for me to build a robot and test it rather than try to calculate
> all this mechanical crap like torque, friction etc.
> http://teamur.netfirms.com/tmr002/tmr002.htm
> It looks that I was wrong.  I put a sprocket directly on the motor's shaft
> and unfortunately the torque was not enough big to move it.  Of course the
> first mistake I made was the size of this sprocket.  Replacing with the
> small one helped a lot.
>
> And here comes the disappointment.  The robot should have a nickname "Jerky"
> because of how it moves!

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email listserv@mitvma.mit.edu with SET PICList DIGEST in the body