Micro Robot using atmega 8

[ameya_muley]

I am trying to make a micro robot. Size is 50mm * 30mm. I want to know different type of motor which are small in size & light in weight & can be operated on 3V 40mAmp CMOS battery. & able to operate directly through PORT pins of AVR. :?:

 

[tpetar]

First better check AVR uC datasheet to see maximum allowed current per pin, plus inductive feedback to pin problem. Better add one small SMD transistor to drive motor.



Check this Nano Coreless 7mm DC Motor - 17mm Type 1,5V 20mA micromotor:

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Datasheet
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[ameya_muley]

Sir, Is this type of motor readily available in the Indian Market. Like in Bombay..??

 

[tpetar]

Sir, Is this type of motor readily available in the Indian Market. Like in Bombay..??

I dont know for that. Check possibility for ordering over Internet.

 

[shatruddha]

Hi Ameya
You can use vibrator motors (say pager motor or cell phone vibrator motor) if weight of your bot is less. you will need to do some calculations to see if they fit your requirements.
These motors are readily available in India. I'm sure you'll find a good deal of them at lamington road.
Or just go to any mobile repairing shop, and ask for cellphone vibrator motor. You can get one for less then 20 bucks. These motors you can control directly using your microcontroller, but its always a good idea to seperate your motor power from controller. Using a smd transistor will do good enough for you and using transistors you can use some logic to invert direction of motion as well.

 

[ameya_muley]

Sir you are absolutely right...

I am also thinking about the same...

but sir may I know the basic specifications of that motor as well as may I drive that motor directly throght the ports of AVR Atmega-8.

I am giving Atmega-8 Supply from two Button CR2032 battery (Connected parallel) with 3V & 80mA.

I want to ask one more thing is that Small size IR Tx&Rx pair sensor for Sensing line (LINE FOLLOWER ROBOT).

 

[fouwad]

try using power window motor in car doors, ull find it on spare part shop

 

[shatruddha]

atmega ports can provide upto 100mA I guess. Current requirement for these vibrator motor are quite small. I'm sure you can use port pins, but its always a good idea to do the testing before actually connecting it to your controller.
connect motor to 3V supply and check how much current it draws. Based on your result, decide if you can use port pins or not.
Tx- Rx pair you can go for smd. That will reduce your size and you can embed these sensors as well on your main board.

Using Power window motors is not gonna work for you, since they are quite big looking at your requirement and they have huge torque, which in your case will be redundent.

 

[ameya_muley]

Sir first of all thanx for guiding me..

I wanna ask one thing that is how can I connect Vibrator Motors of mobile with small tyres / wheels... that the main problem I am facing...

I saw one photo in that he placed motor shaft on to the outer diameter of wheel for providing speed... but dont even uderstand how to arrange all these things..

if possible to guide me with the help of diagram for (Easy understanding) plz help me...

Thanks a lot for continuous help...

 

[tpetar]

atmega ports can provide upto 100mA I guess. Current requirement for these vibrator motor are quite small. I'm sure you can use port pins, but its always a good idea to do the testing before actually connecting it to your controller.

100mA can provide in first few sec after that you get smoke effects.

ATMega8 support up to max 40mA, in datasheet there is notice for running part on maximum electrical values.

Also I find on Internet that people runs 70-80mA from ATMega8 pins with temperature increasing.

I dont see purpose of direct motor running over uC pins, you can use small SMD transistor for this purpose.


Interesting part from ATMega8 Datasheet:




Here you can see some datas for vibration motors:
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Best regards,
Peter

 

[shatruddha]

Yeah you are right
Atmega cannot provide 100mA current.

 

[tpetar]

In general its not smart to use motors and other similar inductive loads such as relay coils direct to uC pins. Better use transistor to drive this loads, there is many reasons for this.

 

[ameya_muley]

ya.. definitely I will use transistors to drive the motors but How can I switch the direction of these motors?

may I have to design the H bridge for that. Will any one please suggest me the alternative option which reduces the weight as well as size of my PCB. any SMD motor driver such as (MOTOR Driver L293D). L293D not available in SMD packages.

:roll:

 

[tpetar]

L293D in SMD:

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H-brisge for driving this micro motor can be very small or should I say micro.

You can use SMD transistors/MosFETs, see tutorial and circuit:

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This H-bridge PCB in SMD for this low power motors can be very small around 1cm-2cm x 1cm-2cm.


DC Motor Tutorial
http://www.electronics-tutorials.ws/io/io_7.html


Best regards,
Peter

 

[shatruddha]

Well, if you are not able to get SMD L293, i would suggest you to design H bridge. As tpetar has given a schematic, for your application you can reduce it to just 4 transistors(TRx). You can remove the flyback diodes and 2N2222 transistors, as your circuit is going to be 5 or may be 3.3v and your controller is sufficient enough to drive the gates of TRx directly. Your motor is quite small and draws very less current, and I suppose fly back current will not be a problem in your case, anyways its always a good idea to use them