### Author Topic: Help In Constructing Simple Circuit To Drive 2 DC Motor..  (Read 2407 times)

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#### drew1.0beta

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##### Help In Constructing Simple Circuit To Drive 2 DC Motor..
« on: September 23, 2008, 10:40:51 AM »
hi everyone..
here's the story,
i'm currently doing an electric wheelchair as my Final Year Project with a partner. We'll be using two 12V dc motor to drive 2 rear wheels. Meaning, two wheels in front are free to roll. Can anyone help us to contruct the circuit? we'd like to have 4 buttons:
a) move forward ( both motors turn clockwise)
b) reverse ( both motors turn anti-clockwise/counter-clockwise)
c) turn left ( only the right motor turns, left motor stops)
d) turn right ( only the left motor turns, left motor stops)

We dont plan to use any microcontrollers ie PIC,PLC ..etc..
only 'normal' circuitry..is that possible?
THANKS ALOT!!
-andrew-

#### Webbot

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##### Re: Help In Constructing Simple Circuit To Drive 2 DC Motor..
« Reply #1 on: September 23, 2008, 12:40:17 PM »
The key information you haven't given is the amount of current that the motors take (each). Not only in normal running but also the stall current (ie when you hold onto the output shaft and stop the motor turning).

You need these values to decide how much power your motor drivers will need to supply.

Seems like you may be better off using a joystick rather than 4 buttons.
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#### ArcMan

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##### Re: Help In Constructing Simple Circuit To Drive 2 DC Motor..
« Reply #2 on: September 24, 2008, 09:12:19 PM »
Well, you don't need a motor driver to do what you want to do.  A simple relay circuit will do.  Better yet, just use buttons that are rated at a high enough current for your motors.

#### Webbot

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##### Re: Help In Constructing Simple Circuit To Drive 2 DC Motor..
« Reply #3 on: September 24, 2008, 09:20:46 PM »
But a relay will give either: full speed ahead, full speed in reverse, or stop. So whoever is in the wheel chair may get flung about a bit. Do you need an 'accelerator pedal' ie do you need to smoothly change the speed?
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#### ArcMan

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##### Re: Help In Constructing Simple Circuit To Drive 2 DC Motor..
« Reply #4 on: September 24, 2008, 09:35:59 PM »
But a relay will give either: full speed ahead, full speed in reverse, or stop. So whoever is in the wheel chair may get flung about a bit. Do you need an 'accelerator pedal' ie do you need to smoothly change the speed?

Yeah.  I wouldn't want to be the test dummy for that contraption.

#### Webbot

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##### Re: Help In Constructing Simple Circuit To Drive 2 DC Motor..
« Reply #5 on: September 24, 2008, 09:42:51 PM »
Yeah.  I wouldn't want to be the test dummy for that contraption.
Hold on - it was YOUR idea to drive it like this - now you've dropped it. Suggest you come up with a better solution - otherwise you will be nominated as the crash dummy  !
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#### drew1.0beta

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##### Re: Help In Constructing Simple Circuit To Drive 2 DC Motor..
« Reply #6 on: September 25, 2008, 09:35:20 AM »
thanks for the reply guys..
full speed ahead is ok i guess.because i'll be using gears..
When the motor runs without load, it's not that fast actually..
so i think i wouldnt need an 'accelerator pedal'..
any pics of how the relay circuit looks like?
is it possible to do it using only push buttons,logic gates and relay?

here's something i did, i doubt it'll work tho.. :/
( its just the circuit for the logics)
when A = ON, Left Probe = high, Right Probe = high (move forward)
when B = ON, Left Probe  = low, Right Probe = high (turn left)
when C = ON, Left Probe = high, Right Probe = low (turn right)
« Last Edit: September 25, 2008, 09:37:14 AM by drew1.0beta »

#### Trumpkin

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##### Re: Help In Constructing Simple Circuit To Drive 2 DC Motor..
« Reply #7 on: September 25, 2008, 12:15:54 PM »
Quote
any pics of how the relay circuit looks like?
Read this http://www.kpsec.freeuk.com/components/relay.htm
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