Newbie working on a robot

Walt&Andy

Hi! My son and I are building at robotic chicken coop (opens and closes the door automatically, activates a buzzer and drops a little feed to call the girls in). We're hoping to raise and lower the door (portcullis style) with a re-purposed cordless drill motor. 2 questions come to mind:

18v cordless drills are *cheap*, 12v are hard to find new or used. What happens if I apply 12v to a 18v DC motor?

How do we control this thing with a BASIC Stamp? Pnp transistor? H-bridge? Relay? Expect any answer you give to trigger a follow-up question about how to wire it up.

Simple answers are appreciated - we're pretty new at this.

Much thanks!

Mike Green

12V vs. 18V drill: Won't run as fast or have as much torque. May run hotter under load, but not much of an issue with occasional brief use. Make sure to use a counterweight and that the door works smoothly.

Use a relay that's rated for enough current (measure the motor's current draw under a realistic load). The Stamp will need a switching transistor (and snubber diode) to control the relay. See Nuts and Volts Column #6 (http://www.parallax.com/downloads/nuts-and-volts-basic-stamps-volume-1) for a discussion of transistor use with a Stamp to control relays and motors.

ajward

doggiedoc did a similar project a while back.

http://forums.parallax.com/showthread.php/142318-It-s-working...-it-s-working!!!?highlight=coop

Walt&Andy

Thanks, ya'll! Will absorb!

electromanj

Congratulations on your project with your son! Sounds like a really fun project.

I second checking out doggiedocs project!

I messed around with a schematic tonight that might help you with your motor control...

This uses two DPDT (double pole double throw) relays to handle reversing the motor. Both relay coils are also interlocked to prevent a direct short in case of program error that would energize both relays at the same time. The only thing I have omitted is a fuse on the supply side. We can figure that out after you guys decide on a motor...

I have attached a couple of schematics on the bottom of this post. The first one is the schematic. The next two are pictures of the states of one relay or the other energized. I tried to color the lines with Paint, but I'm not very good with that so I used some highlighters and took pictures. .....

Can somebody please review my schematics to make sure that I didn't make any mistakes please. Thanks.

traVis.

erco

You can make a fine H-bridge using a pair of more common SPDT relays. No problem if both relays fire at the same time.

http://forums.parallax.com/showthread.php/106382-4-State-Relay-H-Bridge