RE: [CAD_CAM_EDM_DRO] steppers best?

Hi Ebiz (?),



Yes, stepper motors could indeed do it. My first "robot" had a pair of NEMA
#34 steppers hooked up to some surplus 3:1 timing belt pulleys, and a pair
of small cart wheels. I used an 8085 uP (you old timers will remember this
one); I'd suggest a PIC for your 'Bot.



Stepper motors (probably the ones you have) can be driven with a simple L/R
driver if they're unipolar. You know the other driver solutions.



If you want to go the servo route, then the encoders can provide steps
traveled, and accomplish the same task. You just need a transistor to turn
them on (darlington, TIP121?).



If you can put an LCD display on the project, then a few push buttons can
allow you to edit a distance count (you wouldn't *have* to work in
inches/mm, just calculate the required number of steps, and enter it. A
7-segment multiplexed LED display could also work.



Dip switches? That could work, but can take up a lot of bits! SPI can aid
in reading 20 or so bits in serially.



You could use a 4 x 4 switch matrix, and read in decimal numbers. Plenty of
easy-to-find keyboards out there.



I suppose you could also just use 4 dip switches, and an "enter" pb, but you
probably want a way to verify the entry. On a RDF receiver I bought, they
just flash the selected frequency back to you for verification on ONE
7-segment LED. This could work!



Well that boils it down! Use a 16-key keyboard, and a 7-segment LED. That
would be my recommendation at this time.



Good luck! Tell us how you made out!



Alan KM6VV

Currently building a hexapod robot w/ 18 R/C servo motors.

> 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

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