Controlling DC Toy Motor

[marcos.placona]

Hi guys I've been searching on the forum for ways to control a dc toy motor with my picaxe 08m. I found that I need to use a transistor for that to be ablle to use different power source but found so many ways to do that. Now I'm a bit confused on how to do that, I was wondering if I can do it using the cheap bc548b, and if with this one, I would be able to control the forwards and reverse of my motor.

Does any one have a good way of doing that using such transistor? Or will I need to buy the BCX38C?

Cheers

 

[beny1949]

have a look in manual 3... there are several different ways to interface a motor. if you want bi-directional control then a L293D may be the answer.

its all in the book!

 

[MiB1986]

Hello,
assuming your motor is two pole, ie two wires, put them one way and it turns one way, switch the wires and it goes the other way its very simple.

What voltage is the motor, its usually written on it, ie 3v, 6v etc...

yes you will need some form of transistor but this is because of current more than anything as the 08m can only handle little current like 20mA and your motor can probabily pull 300mA if not more.

Any transistor will pretty much do as long as its high power, such the TIP range, i personally use darlington driver chips, these are very easy to use.

IF you use a driver chip you can use the code below.

Otherwise your into Push - Pull Amplifiers, common collector is the best i have found.

for simple code to make the motor turn...


high 1
low 2

and to turn the other way

low 1
high 2

good luck...

 

[marcos.placona]

@beny1949: I've read the manual and that's why I was so confused, 'cause there's several approaches for it, and I wasn't sure about which one would suit the best.

@MiB1986:That's exactly what my motor is, a two pole 3v.

The transistor I have here are the bc548b, and I guess they won't do the job, 'cause as far as I fould find, it will just support up to 100mA

I think I'm gonna buy the BCX38C, as they seem to go s far as 500mA, and it will be enough, I guess.

I just didn't understand very well how to use this transistors and still be able to go forwards and backwards. I know that if I switch the wires, I can have it going both ways, but am not sure on how to "switch the wires" in my circuit and code.

Thanks you very much for your answer,

Marcos Placona

 

[manuka]

Marcos- quick reply sorry. What current drain is your motor? A basic BC547 etec is fine if only modest toy drain. You need an "H bridge" (so called as it's elements are in the shape of an H) for code controlled motor reversal. These can be DIY with transistors, but most folks use the L293D IC. Do a Google. Stan

 

[Michael 2727]

For driving toys/robots you should take into account the Stall Current of the motor being used, if your little buggy or robot arm gets jamed up against an object the full
stall current may be drawn by the motor.
This can sometimes be in Amps.
In many small battery devices the batteries are not capable of delivering such currents, which probably saves the transistors/H-bridge from exploding.
Use suitably rated transistors and a good heatsink if making a DIY version.
you can use MOSFETS as well as BJTs or Darlingtons to make a H-bridge.
Even some small motors can draw 1A in a stall.

 

[Wrenow]

Good point on finding the stall current. Some common toy motors, like the common Mabuchi550 size draw only an amp or so under normal load. But, hit a stall, and they can pop up toabou8t 90A! And some of the guys who put two or 3 of these in their R/C Model Warships wonder why their 20A ESC (electronic speed controller) lets out the magic smoke and stops working sometimes. Or the wiring catches fire. Must be a lousy ESC, they think. Surely it couldn't be anything else, as the motors only draw a total of 6A on the bench, leaving plenty of overhead capacity. But, get some moss on the props, or a rock, or something else that stalls the motors, and the poor little bugger is trying to handle well over 200A! no wonder it gives up he ghost.

The Tamiya Solor Motor 02(?), which is a Mabuchi 500TB, draws less than 1A at stall, by the way.

The ESC's by the way, come in various current handling ratings, some forwards only, others with forwards and reverse. They are controlled by a regular Servo signal , and thus interface nicely to a Picaxe for controlling motors.

Cheers,

Wreno