Let's Make Robots!

Need help on motors and motor driver

Please help me out- I want to make a basic robot like the start here bot but with an arduino micro processor instead of picaxe. Getting enough money to make it is a problem as I've got only $50. So I can't buy a motor shield for the arduino that I will try to assemble myself an a breadboard. I have been through a tutorial that teaches you to make a motor shield using a L293D motor driver but the problem with that is that the stall voltage of motors you can use with it is very low (1.2 V) while most motors that I know of have a stall voltage of greater than 3 V and I'll be using those motors. My question is- if I provide the motors with external voltage of 2.4 volts using rechargeable batteries, which is under the stall voltage and use the motor driver to provide the extra voltage then will the motors work as they do? Will continuous exposure to current under the stall value destroy the motors out will they be fine? Is their going to be any change in the programing part? While answering, please keep in mind that I'm an absolute beginner and using the L293D is my only hope of using a motor driver and staying in the budget.

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I think you have it confused. The 1.2 number comes from the chip's amp rating. It's stall current, not voltage. It can handle voltages up to 36V. You need to look at your motor's stall current and make sure it's under 1.2A if you're going to use the L298D. The stall current is the electricity it uses when the motor is on but held stationary; the worst case situtation. If it pulls more current than the L293D can handle it will burn the chip up. Any current under the chips rated maximum is ok, no damage will be done.

You should also look at the SN754410. Very similar to the L293D but can handle more current (bigger motors) at a similar price.

Jax- Sorry but I'm a bit confused as I've been through many webshops and all of them advertise things differently. I'll look back and post again. SN754410 is no good as it can't make a motor reverse (atleast the blog that I read on making a breadboard motor shield using L293D said so). David- Any good motor which is compatible with the L293D and are cheap will do. If those motors aren't good in quality then please suggest me a tutorial to make my own motor board with a better motor driver.

The SN754410 has the same quad half H-bridge design as the L293D. It does all the same things but with a much longer name :) Same pins, same size, same connections.

The instructable you linked to is the basic schematic to use. You will have forward and reverse capabilities with either chip. There are other ways to set it up but that one is the easiest.

For motors you probably want something like:


or maybe these

This is also suitable (edit: just noticed it has a weird backshaft to it. Maybe not as cool as I thought at first).

This list is nice because it lists what each motor's stall current is right in the description. Be sure not to exceed the 1.2A or 2A, depending on the chip you go with.

I noticed you're in India. Have you seen hobby2go? They only have GM9 motors but maybe they will be cheaper since they are in your country.

The motor that I'm thinking of buying 4 of these- http://arduino-direct.com/sunshop/index.php?l=product_detail&p=120. They seem to look good and cheap. If you have any other suggestions please let me know. Also can you suggest me how many L293D will it take to run these motors. Will 1 be sufficient?

A standard L293D setup a you linked to will not work. Stepper motors are a different beast. They don't take steady current like a normal DC motor, they need fast little pulses to make them move. They tend to use more current than a standard DC motor of similar torque as well. I recommend sticking with the usual DC variety.

you can stack the 293 or the 754410 to nearly double their current handling capability.

Jax- Thanks for the links. Believe me, hobby 2 go is actually costlier than the your duino webshop and many webshops that ship out of China (due to the tax policy of our govt.). Solar botics don't ship in India but the other 3 webshops are good though they may go out of my budget. I think I'll go with the 754410 if there is no difference in the reversing of motors. Thanks for all your help, you as good as saved my life. Birdmun- Thanks, I'll definitely try that sometime.

No problem. You seem eager and I am happy to help. In fact I'll send you an email with another possible option. I have some capabilities that may help you but maybe the taxes will make the offer not very attractive. I will leave it to you to decide.