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Author Topic: motor problem [newbie]  (Read 936 times)

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Offline extreme.alyTopic starter

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motor problem [newbie]
« on: April 03, 2011, 05:44:35 PM »
ok i have a motor, extracted from my rc airplane..and im trying to do sumthing with that motor and teensy 2.0..
when i connect the motor to +5v and ground, it works.. but when i connect it to a pin instead of +5v, and give the pin a HIGH output, it doesnt work.. any idea why?

Offline Kylepowers

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Re: motor problem [newbie]
« Reply #1 on: April 03, 2011, 06:08:50 PM »
Dose the board have a motor controller on it? You need that because the pin even on high setting would not provide the power required for the motor usually. Most boards need a controller between them and the motor.

Offline waltr

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Re: motor problem [newbie]
« Reply #2 on: April 03, 2011, 08:23:40 PM »
How much current (Amps) does the motor draw at 5V?
Most processor output pins can only supply about 25 mA!!!

Offline extreme.alyTopic starter

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Re: motor problem [newbie]
« Reply #3 on: April 04, 2011, 02:54:54 AM »
ohh! thank you! :)

so instead of a motor controller, can i simply use a transistor (or sumthing else)? I have very little idea about transistors..
connect the 'Collector' and 'Emitter' to the motor having a different power source and 'Base' to the output pin?
if yes, is there any 'specific transistor' i'll have to buy or any transistor would work..?

[EDITED]
i just realized that i'll be supplying power to teensy using usb port of my laptop...
so if the above usage of transistor is correct, can i use the OTHER USB port of my laptop as a power supply to the motor? is there any issue?
« Last Edit: April 04, 2011, 03:18:07 AM by extreme.aly »

Offline TrickyNekro

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Re: motor problem [newbie]
« Reply #4 on: April 04, 2011, 05:44:17 AM »
Do you need both speed and direction control, or only speed control?

I can show you some pretty neatty, transistor based circuit, but tell me your needs first ;-)

And it would be much better not to use you usb port to supply current to your motor, better use an external battery...
Motors get noisy, and a computer is a very noisy environment itself.
Unless reckoning for some expensive smoke, and weird odors, please use a battery, especially now that you are a beginner ;-)
For whom the interrupts toll...


P.S. I've been inactive for almost a year... Don't give promises but I'll try to complete my tutorials. I'll let you know when..

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Offline waltr

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Re: motor problem [newbie]
« Reply #5 on: April 04, 2011, 07:53:01 AM »
ohh! thank you! :)

i just realized that i'll be supplying power to teensy using usb port of my laptop...
so if the above usage of transistor is correct, can i use the OTHER USB port of my laptop as a power supply to the motor? is there any issue?

Before any of us can answer your question you need to answer the question I asked, which is:
How much current does your motor draw?

Offline rbtying

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Re: motor problem [newbie]
« Reply #6 on: April 04, 2011, 08:02:38 AM »
It's from an RC plane, so I would think somewhere between 5A and 50A (ie, much more than a USB port can supply)

Offline extreme.alyTopic starter

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Re: motor problem [newbie]
« Reply #7 on: April 04, 2011, 08:49:34 AM »
Before any of us can answer your question you need to answer the question I asked, which is:
How much current does your motor draw?
I have a multimeter.. how can i find out how much current it draws?

Do you need both speed and direction control, or only speed control?

I can show you some pretty neatty, transistor based circuit, but tell me your needs first ;-)
well i need both..but direction control more importantly!

Offline waltr

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Re: motor problem [newbie]
« Reply #8 on: April 04, 2011, 09:28:49 AM »
Quote
I have a multimeter.. how can i find out how much current it draws?
Put a smallish value resistor in series with the motor to power supply. Then measure the voltage drop across the resistor and calculate the current using Ohm's Law.

Quote
well i need both..but direction control more importantly!
Then you will need an H-bridge motor driver or controller.
You will need to know the motor's current before selecting a driver.

Also, list exactly what functions you need for the motor.
If you only need to control the motor's direction and not speed (on at full speed) then a couple of relays can work.

Offline TrickyNekro

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Re: motor problem [newbie]
« Reply #9 on: April 04, 2011, 09:53:59 AM »
Quote
I have a multimeter.. how can i find out how much current it draws?
Put a smallish value resistor in series with the motor to power supply. Then measure the voltage drop across the resistor and calculate the current using Ohm's Law.

And I though that most multimeter come with an amp meter nowadays too....  ;D

Look, if the motor doesn't draw more than 500mA with load (which means you use your hands to stall it - stop it completely from turning and measure the current there)
then some simple transistor solution can come in handy... Or else you can use some ICs like the L298N which will do for currents up to 3A ( I think it's somewhere there) with sufficient heat sinking.
And there other ICs that can handle even bigger loads...

For very heavy loads way up the 10A you will need unfortunately a MOSFET approach...
MOSFET way seem easy to use, but they are tough sons of b..... The gate capacity can completely ruin the driving circuit, so do really rely on what google shows up... Most circuits there are made by hobbyists and don't take into consideration many many things...


Best Regards, Lefteris
Greece
For whom the interrupts toll...


P.S. I've been inactive for almost a year... Don't give promises but I'll try to complete my tutorials. I'll let you know when..

Cheers!

Offline extreme.alyTopic starter

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Re: motor problem [newbie]
« Reply #10 on: April 04, 2011, 09:57:26 AM »
Put a smallish value resistor in series with the motor to power supply. Then measure the voltage drop across the resistor and calculate the current using Ohm's Law.
okay, teensy gives me 5.00v..i connected a 330ohm resistor and motor in series... now the voltage across the resistor is 4.5v-4.6v..that make 0.014A... 15mA correct?
but the motor is not working.. =s when i remove the resistor, it starts running again.. is that fine?

EDITED
oh i forgot to tell you that, the motor i'm using is of the TAIL of the helicoptor for now..it is a very small motor..shouldnt have power problem for now..
« Last Edit: April 04, 2011, 10:41:09 AM by extreme.aly »

Offline waltr

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Re: motor problem [newbie]
« Reply #11 on: April 04, 2011, 10:53:04 AM »
The resistor value is too large. Try a smaller value resistor, less than 10 Ohm maybe even 1 Ohm.

Your current calculation is correct but the motor needs to run with the resistor in series. Try for a resistor value that gives less than a 0.5 Volt drop or even less.

Also, measure the Voltage drop with the motor stalled as Tricky Nekro suggests.

Offline Soeren

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Re: motor problem [newbie]
« Reply #12 on: April 04, 2011, 04:17:55 PM »
Hi,

okay, teensy gives me 5.00v..i connected a 330ohm resistor and motor in series... now the voltage across the resistor is 4.5v-4.6v..that make 0.014A... 15mA correct?
but the motor is not working.. =s when i remove the resistor, it starts running again.. is that fine?
You should do it from a separate 5V supply, not from a microcontroller output with a 40mA limit and neither from an USB port.

The reason it drops 4.5 to 4.6V over the resistor is because the pin cannot supply the current needed by the motor (which have 0.4V to 0.5V at the 13.6mA to 13.9mA).

It does however tell us that the motor will consume somewhere between 136mA and 174mA when a proper 5V supply is driving it (had you been more precise, so could the calculation be).

Even if the motor could run from the pin, it would destroy it in a short time, as it's an inductive load and can generate large peak voltages.

So, put the teensy, the various resistors etc. aside for the moment and connect the motor to a 5V supply via the 200mA range of your DMM, which will give you a direct readout of the current drawn. Then tell us what it amounted to.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline TrickyNekro

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Re: motor problem [newbie]
« Reply #13 on: April 04, 2011, 11:38:23 PM »
Doesn't your Multimeter have an amp meter???

That can't be really! Unless it's 3$ cheap...

Best of all, use the amp meter in series with your motor and a separate power source such as a battery....
For whom the interrupts toll...


P.S. I've been inactive for almost a year... Don't give promises but I'll try to complete my tutorials. I'll let you know when..

Cheers!

 


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