Author Topic: L298n Module help!  (Read 5929 times)

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Offline MrOmnos

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L298n Module help!
« on: December 11, 2015, 02:19:07 pm »
Hi, I making a bot for "robot sumo fight" competition. Bots are place on a platform of 2m meters diameter and to win one needs to push others off the platform. The max weight is 3kg for the bots. (Assume the motors need to push max 3kg of weight) I am using 4x200rpm geared motors for the 4 wheels. I don't know the stall torque.
I am going to use the L298n module..
This one

I looking to drive the motor in way to get the max torque out of them.
Max current rating of this module is 2Amps per output in both direction.
I will using a 12volt supply. 24 volts is max volts that is allowed in the competition.
Will I be able to drive 2 motors from one output without out overloading the IC and still get good performance from the motor? Since, both motors on the same side will be getting the same control signals from the micro controller at any given time so I thought one motor driver module should do.
 

Online wraper

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Re: L298n Module help!
« Reply #1 on: December 11, 2015, 02:53:05 pm »
You have no chance of winning any barely serious competition with the motors which won't burn this IC. Serious guys use 150W (nominal) Maxon motors which have 70A stall current at 24V nominal voltage or twice of that for 12V versions (and overvolt them too).
 

Offline Asim

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Re: L298n Module help!
« Reply #2 on: December 11, 2015, 02:56:03 pm »
Depends on the motors you are using, if one motor under maximum load is consuming less than 1A. This means that parallelling two motors in one chanell will require less than 2A.
If you have the motors in hand , supply one of them with 12V and load it and measure the maximum current , if it is more than 1A then the proposed module will not handle it
 

Online wraper

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Re: L298n Module help!
« Reply #3 on: December 11, 2015, 02:56:40 pm »
 

Online wraper

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Re: L298n Module help!
« Reply #4 on: December 11, 2015, 03:01:51 pm »
Also, don't even try 4 wheels, it will be slow and clumsy. 2 wheels and the blade on the front is the way to go. And don't forget that serious robots have magnets  on the bottom with tiny clearance to the platform which easily make 100 kg pulling force towards the platform (steel top)
« Last Edit: December 11, 2015, 03:09:21 pm by wraper »
 

Online Ian.M

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Re: L298n Module help!
« Reply #5 on: December 11, 2015, 03:04:44 pm »
No.   The L298 is a fairly old and crappy bipolar H-bridge chip.  It wastes a lot of the available voltage as the Saturation Voltage of its output stage is quite high (e.g. its 3.7V @ 2A combined high side and low side drop which is 30% of your 12V supply).  You would do far better with a discrete MOSFET H-bridge module which will deliver closer to 95% of the supply to your motors.

Before you can choose an H-bridge, you need to know the stall current for your motors, and have some idea of the peak current at the point you loose traction.   Make a jig that lets you press a block hinged at one end against the tyre of one of your wheels.  The block should be surfaced with the same material as the arena for your robot class.  Apply a force of 1/2 your maximum down-force per wheel using a spring balance in line with the wheel, at a right angle to a point on the block twice as far from the hinge as the point of contact with your wheel.  Measure the current when the motor is powered at your maximum battery voltage. 

For the stall current, it may be possible to stall it through the gearbox, but if the motor is detachable, it may be safer to put a collar direct on the motor shaft and put a clamp on that.   Don't leave the motor stalled for more than a couple of seconds or you will overheat it and burn it up.
« Last Edit: December 11, 2015, 03:39:01 pm by Ian.M »
 

Offline MrOmnos

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Re: L298n Module help!
« Reply #6 on: December 11, 2015, 03:06:21 pm »
Oh! I forgot to mention the $$ limitation of the competition. Even without the cost limitations, I don't think anyone can afford a 300$ motor for a robo fight in a Nepal. That is more than the prize money.
Depends on the motors you are using, if one motor under maximum load is consuming less than 1A. This means that parallelling two motors in one chanell will require less than 2A.
If you have the motors in hand , supply one of them with 12V and load it and measure the maximum current , if it is more than 1A then the proposed module will not handle it
I was thinking the same.Just wanted to be sure. Thanks!!
 

Online wraper

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Re: L298n Module help!
« Reply #7 on: December 11, 2015, 03:11:48 pm »
Oh! I forgot to mention the $$ limitation of the competition. Even without the cost limitations, I don't think anyone can afford a 300$ motor for a robo fight in a Nepal. That is more than the prize money.
There are cheap Chinese motors which are inferior to Maxon but still will blow away by an order of magnitude what you are trying to do.
« Last Edit: December 11, 2015, 03:17:19 pm by wraper »
 

Offline MrOmnos

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Re: L298n Module help!
« Reply #8 on: December 11, 2015, 03:23:14 pm »
Oh! I forgot to mention the $$ limitation of the competition. Even without the cost limitations, I don't think anyone can afford a 300$ motor for a robo fight in a Nepal. That is more than the prize money.
There are cheap Chinese motors which are inferior to Maxon but still will blow away by an order of magnitude what you are trying to do.
Where can I buy that piece of destruction??
« Last Edit: December 11, 2015, 03:25:50 pm by MrOmnos »
 

Online wraper

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Re: L298n Module help!
« Reply #9 on: December 11, 2015, 03:33:23 pm »
BTW is there mentioned if the platform is magnetic or not and particularly written something about using magnets? If those are some low end competitions, there is possibility this is made of wood so there be no advantage of high power motors.
 

Online wraper

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Re: L298n Module help!
« Reply #10 on: December 11, 2015, 03:40:31 pm »
Where can I buy that piece of destruction??
I've certainly seen some high power DC motors on aliexpress a while ago. The cheapest option is BLDC for RC models, like used in helicopters and quadcopters, they are power beasts for their power/size ratio and are insanely cheap. But they are hard to control and have high RPM therefore need gearbox with higher ratio than DC motors.
 

Offline MrOmnos

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Re: L298n Module help!
« Reply #11 on: December 11, 2015, 03:51:33 pm »
Yes, it's a low end competition. The platform will be wooden painted white in the middle and black on the edges.
 

Online Ian.M

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Re: L298n Module help!
« Reply #12 on: December 11, 2015, 03:58:20 pm »
Painted with what?  it makes a big difference to the coefficient of friction.
 

Online wraper

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Re: L298n Module help!
« Reply #13 on: December 11, 2015, 05:57:26 pm »
The platform will be wooden painted white in the middle and black on the edges.
That's strange. Normally platform is black in the middle with white edge.
 


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