Re: [CAD_CAM_EDM_DRO] steppers best?

Steppers are easy, but the rest of this depends I think ...
If you have a stepper driver and feed steps into it, the motor moves.

What are you allowed to do re: electronics ? Can you buy stuff ?
Budget 10$ or 100 $ or ?
One option you have would be an electronic timer ?
I.e. n milliseconds, with the stepper triggering at x intervals. This
would give you an absolutely correct traverse, as long as you
mechanicals are not overloaded. Some kind of 555 timer, or a commercial
timer (some commercial timers may be 5-10$ on ebay), but is it allowed
or within the rules ?

Is the goal to make the 5-10 m traverse as fast as possible or as
accurate as possible ?
Can you buy a stepper driver kit and build that ?
This would allow you more possibilities, and they are cheap (a.20$).
For speed, you would need to to get some kind of ramping into it, if the
goal is to go the distance as fast as possible. You might be able to do
it with a timer, and 3 pots and some kind of decay i.e. one adjusts
acceleration time, one adjusts hi-speed time, and one adjusts
deceleration time.

If you can make/build/buy a kit for an electronic timer or counter, for
x steps, and program it onsite, you might get something very accurate.
If electronic control of acceleration is too much, maybe caps to boost
the amps on acceleration ?

I believe counters are very easy to do with basic microchips, but have
never done them.
Can you use the web to look up a sample electronic circuit, and then
build and use that ? Parts are likely to be 5-10 $.

If you want, you could hook up an lcd so you can show the set number of
steps to everyone. It would look cool, and add little to the cost or
complexity.

Sounds like fun, good luck

>
> We (high school kids and I) are building a small electric car for a
> competion. It must be 40 cm by 25 cm and be calibrated to travel
> between 5 and 10 m. We'll be told the exact distance at the
> competition. We have a VEX kit (and encoder for it), a Legos RCX,
> small perm magnet DC motors with a PWM controller, and lastly some
> salvaged steppers from a FAX. We could do something "crude" and use
> some rev counter (threaded rod, fishing line wrapping on spool etc) to
> turn the switch off, and coast to a stop, but I'd like to try
> something a little more sophisticated.
>
> I'm looking into being able to run the VEX without a radio control -
> autonomous only, and then jumper, or have a set of DIP switches to get
> various distances, but am not sure it I can run without radio control.
>
> We could also do a timed drive with the RCX.
>
> But I'm leaning toward steppers. We just salvaged some nice little
> units from a FAX - 7.5 degree, 100 ohm, no torque measurement yet, but
> I think they'd move our little car pretty easily. Our level of
> expertise with steppers is that we can make them do single steps with
> a 4 switch/diode test setup in David Benson's Easy Steppin'. So we
> have a ways to go to get the 5 - 10,000 steps we'd need to get the 5 -
> 10 meters, and my questions are these -
>
> 1 -Are steppers our best choice?
> 2 - Is it pretty easy to do the microcontrolling effort to choose a
> certain number of steps (DIP switches etc) and then stop, or is this
> more like an iceberg - a lot deeper than it looks?
> 3 - Other considerations?
>
> I'm the guy who was looking for the Allegro 5804s a month ago who want
> to get something to "move" as one goal. We just learned of this
> competition, in the last couple weeks, and it looks like a nice path
> to take wrt "motion control".
>
> Thanks
>
>