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Topic: The motor saga contiuous -Chapter L298N (Read 5041 times) previous topic - next topic

Tjaart

Hi All
I am having trouble to drive two 3.6v dc motors with a L298N driver.( not the shield). $) See i found battery operated screwdrivers on special, at half the prize of a normal geared DC motor. 8) AWESOME !!!!!!!.......not

Printed in motors: RS380S               from Google: no load> 200mA, loaded> 0.8 A, stall> 24A.
With massive torque from being a screwdriver and only going to drive smallish wheels it will never get to stall, and they come with a slip clutch. even comes with rechargeable battery's and charger.

The built: laptop to arduino uno and L298N and there she goes....and there she goes.....    :smiley-eek-blue:  ARW
the motors only sit there and wine/buzz.
After a lot of Google and reading this: http://forum.arduino.cc/index.php?topic=206825.0

1. Possible issue could be that the L298N Vs = 5V-50V ( at the time of selecting a suitable driver the data sheet only specified 50V,
   google suggested the threshold? of 5V)
? If this is the issue what about supplying the motors with 5.5V
? Could the wining/buzz be caused by my code
?( Now before I wire it all up again and post a video of it on Youtube ) Reading the above mentioned post.
  WHAT is the save way to wire up motors/ inductive loads to and arduino powered by the laptop usb.

Kind Regards

jremington

Quote
WHAT is the save way to wire up motors/ inductive loads to and arduino powered by the laptop usb.

ALWAYS use a separate power supply to power motors, not the Arduino and not a laptop USB port. Be sure to connect all grounds together.

A motor briefly draws its stall current when it starts up.

The L298 driver is good for small, relatively high voltage but low power motors, but not yours. Use a modern motor driver like those available from Pololu.  http://www.pololu.com/category/11/brushed-dc-motor-drivers

ajofscott

For that price he could buy several GWS Brushed ESC units with 2 Amp BEC

MarkT

If the stall current is 24A, then that's what will flow(*) (if only briefly).  If you reverse
the motor suddenly you'll get _twice_ that, briefly.

(*) If the power supply can provide it.  If not the power rail will "droop" (actually it
is crowbarred to near zero volts), and in the L298 this then crowbars the 5V supply
as well, as the chip has in built diode between the supplies.

The L298 is good to an amp or so, 2A with forced cooling, its totally inadequate
for this motor.  Proper high-current MOSFET or MOSFET H-bridge is more the thing.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

keeper63


If the stall current is 24A, then that's what will flow(*) (if only briefly).  If you reverse
the motor suddenly you'll get _twice_ that, briefly.


You'd probably never want to "suddenly reverse" any gear motor of such a nature anyway, simply because under load (provided your power supply and controller could handle the current) you would likely damage the geared transmission or other mechanical components. Whether you cared or not would depend on the application, I suppose.


The L298 is good to an amp or so, 2A with forced cooling, its totally inadequate
for this motor.


2A per channel - but you can parallel the channels and get ~4A for a single motor (again, you would need a large-(ish) heat sink and/or forced cooling).


Proper high-current MOSFET or MOSFET H-bridge is more the thing.


To the OP:

If you can't afford such a bridge, and you want to build your own high-current bridge, my advice would be to go for a hybrid approach that uses a (high contact current) relay (1x DPDT) or two (2x SPDT) for the h-bridge (directional control), and a single high-amperage logic-level N-channel MOSFET on the low-side for PWM (speed) control (just don't switch the contacts of the relay while PWM is engaged!). Such a system is fairly inexpensive (ideal relay would be a couple 40A Bosch automotive SPDT relays), since you only need to worry about that single MOSFET.

Otherwise, don't attempt to build your own, as you will likely end up spending more money burning out components as you build and test the bridge, than you would had you purchased an already assembled bridge yourself. There are many good ones out there that don't cost much, so do your homework. That way, you don't have to worry about all the other hairy aspects of an all N-channel (the cheapest MOSFET bridge to make) h-bridge, which include special high-side driving issues, proper PWM control to keep the high-side voltage boost happy, etc - plus the extra MOSFETs, as they blow, can start to get expensive quickly.
I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.

Tjaart

Hi MarkT and cr0sh
Thank you for your reply. I would indeed want to built an H-bridge for this motor just to learn how to go about matching the motor up to the bridge components.
But that besides the point. I do not think that a little  3.6V motor from a DIY supermarket screwdriver, could really draw 24A amps from it's cheap rechargeable battery's.
I am going to physical  measure the amps this motor draws.,.....   Need to find a way to measure  highish amps with my multimeter.
Multimeter has two settings ...mille-amps....and up to 10A setting.

What about the 5V threshold of the L298n and my 3.6v motor? Maybe supply my 3.6V motor with 5.5V???
And the saga continuous ........ :D

Tjaart

:)
Had 20 min to spare....
The motor draws +/-  0.8 amps free running and attempted stall: +/- 2A. Being intended for a screw driver its has to much torque to stall by hand. ( It's only going to drive a little wheel).
I need to change the wiring coming and going to the motor, it needs to handle larger currents. I did not expect this much current. They get a bit hot and will not last.
Will test it again after and update.
=(

Tjaart

Still no running motor =(
Atached thicker wires and re tested:
http://youtu.be/VjgUv_Dxkbs
http://youtu.be/LgqFLhy65Gg

The motor stalled to max of 4A
so I ordered these parts:
http://www.pyroelectro.com/tutorials/h_bridge_4_transistor/
This is a h-brigde that could handle up to 10A
Will this work?

jremington

#8
Jan 15, 2014, 04:52 am Last Edit: Jan 15, 2014, 04:57 am by jremington Reason: 1
The RS380 seems to be quite popular and cheap. You can buy it many, many places on line. These guys http://banebots.com/pc/MOTOR-BRUSH/M3-RS380-72 give the stall current at 7.2 volts as 21 amps and the peak efficiency amperage as 3.6 A.  As others have pointed out, the L298 H-bridge won't work. The 10-A one you linked probably won't either.

Tjaart

Hi Jremington
=( why would the 10A one not work ? It will never stall driving a little wheel.
What do you suggest I get to drive this motor?

I wanted to learn how to design/make a h-bridge but giving up on that.
I just need this motors to run.

jremington

The problems have been explained several times in this thread, but you are not reading them. For example:
Quote
If the stall current is 24A, then that's what will flow(*) (if only briefly).  If you reverse the motor suddenly you'll get _twice_ that, briefly.


If you want to use the L298 H-bridge and a motor to drive a "small wheel", get a different motor. If you want the RS380 motor to be properly controlled, you will need a 20-30 amp H-bridge like those linked previously.

Tjaart

I thought I could get away with a 10A one...     very new/green to electronics/arduino even posting in forums. :smiley-mr-green:
So I need something in the 20 to 30A range. Now I understand better what the links to other motor drivers is about.
Will go through them again.

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