(Hopefully) a simple problem

Jan 22, 2007 6 Replies
K

I have a simple drive system for a home-made robot. It used 2 windshield wiper motors and a 12V battery. I have 4 relays under computer control (NC, GND, NO) and I'm trying to design a circuit to apply forward and reverse voltage to each motor, giving maneuverability.



Trouble is I can't design the circuit using a single 12V battery, using two and creating +12V and -12V makes it easy - but this means that the forward battery will drain faster than the 'reverse' battery.



Is it possible to do this with just 1 battery and the relays?



Vote
Twitter Facebook LinkedIn
D

How about....

1 relay interrupts the 12V supply for motor on/off control. Another DPDT contact relay does the battery polarity reversal for forward/backward control. D from BC
Vote
Twitter Facebook LinkedIn
T

Search for "H-bridge". It's a standard problem, with a standard solution.

Try not to connect battery + to battery - too often.

Tim Wescott Wescott Design Services http://www.wescottdesign.com Posting from Google? See http://cfaj.freeshell.org/google/ "Applied Control Theory for Embedded Systems" came out in April. See details at http://www.wescottdesign.com/actfes/actfes.html
Vote
Twitter Facebook LinkedIn
C

Yes you can use 2 spst relays for each motor and reverse the polarity:

both NC to minus both NO to plus OP to motor

both relays on or off no motion ry1 on fwd ry2 on rev.

Dave

Vote
Twitter Facebook LinkedIn
P

Use two relays for each motor, one on each motor lead, connected so that when the relays are not energized, they connect their motor lead to ground, and when they are energized, they connect the lead to the positive supply.

With this scheme, when the relays are not energized, both motor leads are grounded, so it doesn't move. When one relay is operated, its lead goes to +V, and the motor turns one way. Operating the other relay will make the other lead +V, and the motor will turn the other way.

If you happen to energize both relays together, both motor leads will be at +V, and again, it won't move.

Peter Bennett, VE7CEI peterbb4 (at) interchange.ubc.ca new newsgroup users info : http://vancouver-webpages.com/nnq GPS and NMEA info: http://vancouver-webpages.com/peter Vancouver Power Squadron: http://vancouver.powersquadron.ca
Vote
Twitter Facebook LinkedIn
G

Do you have some spare sperm to donate? I'm being obtuse here to avoid the possibility of alerting my competitors to your existance.

DNA

Vote
Twitter Facebook LinkedIn
C

And use relays with a break-before-make contact configuration...

Chris

Vote
Twitter Facebook LinkedIn

Join the Discussion

Have something to add? Share your thoughts — no account required.

Didn't find your answer?

Ask the community — no account required