# (Hopefully) a simple problem

K

#### [email protected]

Jan 1, 1970
0
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?

D

#### D from BC

Jan 1, 1970
0
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?

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

T

#### Tim Wescott

Jan 1, 1970
0
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?
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

"Applied Control Theory for Embedded Systems" came out in April.
See details at http://www.wescottdesign.com/actfes/actfes.html

C

#### CheapscateDave

Jan 1, 1970
0
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?

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

P

#### Peter Bennett

Jan 1, 1970
0
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?

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

G

#### Genome

Jan 1, 1970
0
Peter Bennett said:
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

Do you have some spare sperm to donate? I'm being obtuse here to avoid the

DNA

C

#### Chris Jones

Jan 1, 1970
0
Peter said:
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.

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

Chris

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