# owi arm and arduino power supply

I’m trying to control my owi arm using arduino and l293d IC. The motor wouldn’t run from the driver output. I tried powering the motor driver using external power supplies rated at 500mA and 1A. When I check with a multimeter across the driver output terminals there’s a voltage difference of 4.7V. But the motor doesn’t work most of the time. Occasionally it works for a few seconds. What could be the problem?

Hi, Welcome to the forum.

Please read the first post in any forum entitled how to use this forum. http://forum.arduino.cc/index.php/topic,148850.0.html . Then look down to item #7 about how to post your code. It will be formatted in a scrolling window that makes it easier to read.

Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?

Can you please explain what an " owi arm" is?

Thanks.. Tom... :)

What are the specifications of the motor (rated voltage and stall current)? What are the specifications of the power supply (rated voltage and current)?

While you are reading the page linked by TomGeorge, look at #11, too.

Owi robotic arm has 5 geared dc motors which is designed for manual control with d size batteries.
I’m using matlab to control the arduino and here’s the complete code for rotating the base motor.

``````clear a;

a = arduino();
while (pot1 >= 0 & pot1 <= 4.90)

writeDigitalPin(a, 'D8', 1); %rotate base towards left
pause(0.5);
writeDigitalPin(a, 'D9', 0);
pause(0.5);

if  (pot1 <= 0.01 | (pot1 >= 4.90))
writeDigitalPin(a, 'D8',0);
pause(0.5);
writeDigitalPin(a, 'D9', 0);
pause(0.5);
break
end
end
``````

The ‘pot1’ in my code refers to the potentiometer that I’ve used for position feedback.
The power supply steps down the supply from mains to 5V at 500mA using transformer and 7805.
The motor’s rated voltage is 3V and stall current is 3170mA.
I’ve attached the motor specifications and circuit connections.

Your power supply = 5V at 500mA. The motor stall current, at 3170mA, is over 6 times more current than the power supply can supply. The stall current is drawn every time that you start the motor. You need a power supply that can handle the stall current of the motor. And if you will start more than 1 motor at once, a power supply that can handle the combined stall currents.

Can you suggest some viable alternatives? Can I safely assume that my driver IC can handle that much current?

The ancient and inefficient L293 motor driver sucks up 2V itself, so you need a 5V motor supply to get 3V to the motors and 3A times how many ever motors that can start at the same time. So 5V 15A would be the very minimum, in my opinion. I would also use a separate supply for the Arduino and sensors as motors put a lot of noise on their supplies. Your 5V 500mA supply could be good for the Arduino supply. L293 motor drivers are not going to be happy with 3A either.

I can also suggest that you have a look at modern motor drivers like the ones from Pololu.

Hi,
Thanks for the schematic;

Is that really how you have the transformer connected to the LM7805?
I think you are missing some wiring.
Where are the bypass capacitors that the data sheet for the LM7805 recommends.

Thanks… Tom…

@TomGeorge I’m pretty sure that’s how I’ve connected the transformer and the 7805… But that really isn’t much of a concern to me cuz I’ve tried several other regulated power supplies too and the same result- motor doesn’t run. Here’re the pictures… they’re a bit too messy… but I can a send a zoomed in pic of any particular connection if you need them.
Thanks.

@groudFungus thanks for your suggestions but I think I’ll have to all explore my chances with l293d first as that’s the only driver IC that I have at hand now.
So I tried to power a single motor and driver IC with a regulated power supply having a maximum current delivery of 5A… but still I couldn’t get the motor to run. What confuses me the most is that when I started working on this a few weeks back the motor was running even when I powered the driver IC from the arduino 5V supply (which I later discovered was a very bad idea). Anyone here who could shed some light on what could be going on?

Hi, Can you post where you got the motor driver module please? Re-draw your circuit diagram, there is a problem with how you have connected the transformer secondary, and you need more than 470uF of filter capacitor. How many terminals are there on the secondary of the transformer? What are the specifications of the transformer?

The pictures you posted show the UNO with more than just the 4 wires you show in your diagram.

Can you post a picture of your transformer and the circuit you have connecting the LM7805. Have you looked at the LM7805 data sheet and seen how to place bypassing capacitors around it?

Can I suggest you pull ALL the wiring off your project and then re-wire it SLOWLY, the pictures show so many wires compared to the circuit diagram.

Do you have a DMM?

Thanks.. Tom.. :)

@TomGeorge I think I bought the driver module online in 2017. Yes, there are 3 terminals on the transformer secondary, the middle one is simply grounded. Transformer rating- 12-0-12 V, 500mA. (I had tried with several other company designed regulated power supplies too but still the same results...) The extra wiring on the picture are just the ditto of what I had drawn but for 2 other motors.

Someone who had faced the same problem suggested that I power the motor driver with the12V suupply from microcontroller development board. So now my motors runs at a greater than 12V voltage from the l293d output. I know this runs the risk of damaging my motors but for now I'm going to concentrate on the rest of my project and come back to this later.

Thanks for all your support :)