Arduino Forum

Using Arduino => Project Guidance => Topic started by: TyErd on Apr 25, 2012, 02:56 am

Title: dc motors help.
Post by: TyErd on Apr 25, 2012, 02:56 am
Hey guys, for a project, i want to be able to power 4 DC motors.

Motor rated voltage: 7.2V
Motor stall current: 2.5A

I only need these to go one direction but I want to be able to control when each motor stops and starts. I've heard transistors are the best way to go for this. If it is, do I need a transistor for each motor? and then connect each base to an output pin on the arduino. Are TIP122 transistors good for this?

Also do i need a potentiometer for this? if so is one enough?
Title: Re: dc motors help.
Post by: rytcd on Apr 25, 2012, 07:13 am
to be clear, these motors will be moving individually?
Title: Re: dc motors help.
Post by: TyErd on Apr 25, 2012, 09:43 am
its a tank that im making. When it goes forward, all 4 motors will move turn so it moves forward. When it needs to turn left for example, the motors on the left will turn off and the motors on the right will keep running.  
Title: Re: dc motors help.
Post by: rytcd on Apr 25, 2012, 10:07 am
I'm curious, why 4 motors instead of 2?
Title: Re: dc motors help.
Post by: TyErd on Apr 25, 2012, 10:29 am
I might actually use 2 motors, it would be easier... but with 4 motors its faster. But speed isn't really important at this stage, so lets just say I'm to use 2 motors instead of the 4. Would i have to use 2 transistors? connect the base of each transistor to two output pins on the arduino? Also do i need multiple potentiometers for this?
Title: Re: dc motors help.
Post by: nickn4 on Apr 25, 2012, 10:42 am
i think you might be bether off with a Motor Driver / H-bridge since they can offer you to control speed & reverse motors.

it will also help you to study more on the arduino since this will be a little different than just two transistors
btw: i build a schematic once wich (in threory) allowed me to drive & reverse both motors independently with transistors and only 4 data lines to the arduino, but the schematic failed (still not sure why) but i think because the current did not get stable in some way.. soo i dont recomend using transistors
Title: Re: dc motors help.
Post by: AWOL on Apr 25, 2012, 10:58 am
If you want fully solid-state control of speed and direction you'll need at least four transistors (bipolar or MOSFETS) per motor to make an H-bridge, which will also give you braking.
Or, you could do the reversing with a DPDT relay (which will still need a transistor to drive it), and the speed control could be done with a single transistor, or, more likely a Darlington pair or a logic-level MOSFET.

If this is a tracked tank, you'll need to make sure your motors are running at pretty much the same speed if they're driving different sprockets, or you'll run the risk of shedding the track.
Title: Re: dc motors help.
Post by: TyErd on Apr 25, 2012, 11:56 am
I don't need speed control, just to be able to turn on/off...
Title: Re: dc motors help.
Post by: AWOL on Apr 25, 2012, 12:00 pm
on/off in one direction only?
Title: Re: dc motors help.
Post by: TyErd on Apr 25, 2012, 01:34 pm
yep, i'm only gonna use two motors now.
Title: Re: dc motors help.
Post by: AWOL on Apr 25, 2012, 01:38 pm
In that case, a single transistor will do the trick.
Still waiting for the motor specifications.
Title: Re: dc motors help.
Post by: TyErd on Apr 25, 2012, 10:21 pm
what i said in my 1st post is all i know unfortunately. and that Output shaft stall torque: 10Kg/cm Gearbox ratio: 86.8:1 but i don't know how much of that is helpful.
If one transistor isn't enough, I could just simply add another right? Also if i inserted a potentiometer, do i only need one?