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Topic: RC Car / Motor Control Problem (current??) (Read 3 times) previous topic - next topic

luc373

Hey guys!

I'm pretty new to electronics and arduino, even though i've gone thru a heck of lot of tutorials.. I feel comfy enough to build a self made rc car and my problem is that i just can't get my motors for the wheels to work properly!
I'm using 2    3.3v / 3a motors and when not attached to anything (besides my arduino of course) they work fine without a problem, but when i try to build them into my car they are too weak to push it..

Of course i know that the arduino isn't providing enough current for 1 motor so i've tried to use some h-bridges, right now i tried the l298n which supports 2A per channel but it seems like that won't work either.
Now if i'm connecting 2AA batteries directly to the motor it pushes the car without any problem.. What am i doing wrong??

oric_dan

What is the gear ratio on the motors. How fast do they turn when unloaded? How heavy is the car?

groundfungus

The L298 drops about 2V (depends on current).  That doesn't leave much to drive the motor with a 3V supply.

StanD

Is the DC motor geared down? If not that will explain why it does not have enough torque when you put load (the car weight) on it.
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luc373

i tried hooking it up to a stronger power supply because of the voltage drop but it didn't change anything either.. :/

The motor is geared 1:25, rotation speed of the motor is 4000-14000 nnp (at 3A), the card with everything together weighs  +-1kg

i have to say that i tried different h-bridges and no matter which one i used it seemed like the motor was always going the at the same speed with enable pin at 255.

TomGeorge

Quote
Now if i'm connecting 2AA batteries directly to the motor it pushes the car without any problem..


So without the arduino controlling the motors 3V will run the car on the ground or just freewheel?

Quote
i tried hooking it up to a stronger power supply because of the voltage drop but it didn't change anything either.


Stronger????? Higher current or higher voltage supply?
groundfungus is saying that with 2V of the 3V from the battery being dropped across the controller, your motor is only getting 1V to run.
You should try a 5V supply, this will have 2V drop on the controller and leave 3V for the motor.
To help we will need a circuit diagram and a photo of your project to debug and program problems.

Tom... :)
Everything runs on smoke, let the smoke out, it stops running......VK3DMK

luc373


So without the arduino controlling the motors 3V will run the car on the ground or just freewheel?


it will run the car on the ground



Stronger????? Higher current or higher voltage supply?
groundfungus is saying that with 2V of the 3V from the battery being dropped across the controller, your motor is only getting 1V to run.
You should try a 5V supply, this will have 2V drop on the controller and leave 3V for the motor.


i changed from 2AA to 4AA so basically from 3v to 6v, didn't change anything (though the h-brigde was gettin hotter)

groundfungus

If the drivers are getting hotter, then they are dissipating more power.  Where is the extra power going if not the motors? 

luc373

Can't tell,  the only thing that is connected to the driver is the motor .. :/

TomGeorge

Hi, looks like we are going to need a copy of your sketch and circuit diagram to see where your problem is.

Tom... :)
Everything runs on smoke, let the smoke out, it stops running......VK3DMK

luc373

#10
Nov 25, 2013, 04:45 pm Last Edit: Nov 25, 2013, 04:47 pm by luc373 Reason: 1
i removed everything i could and that is what i am left with:


i didn't draw the current sense pins from the l298n in the schematic but they are both wired to ground.
the schematic is pretty shitty sorry..


+ i added a picture of the motor & the gearing

luc373

#11
Nov 25, 2013, 05:44 pm Last Edit: Nov 25, 2013, 05:47 pm by luc373 Reason: 1
ok.. now i just feel like an idiot...

the circuit works perfectly fine, even though i should take some flyback diodes into consideration..

the main problem was, that the motor was powered fine by just 2AA batteries that were already quite used, but they where for some reason to weak to be used with the h-bridge even if i used 4 of them... now that i replaced them with completly new ones everything works just fine...

maybe the used batteries where not providing 6v but just like 3-4 so after the voltage drop of the h-bridge there was only 1-2v left? is that possible?

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