rocinante
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Re: A+ killed by a L298N

Fri Feb 13, 2015 5:39 pm

Ravenous wrote:Oh, also as Joan says, more voltage on the battery will help turning too.

I've never used the L298, only the much smaller L293D (though with both sides wired in parallel), and they are enough for quite a heavy robot at 12V! I really think your L298 is good enough.

Also - your diagram shows 6 alkaline AA cells. Note that alkalines can have problems supplying high current, which tank tracks will need when turning. When I did some experiments with a 4 wheel drive robot, I measured current draw when turning, and it was probably 2x or 3x the straight-line current. With a tank track it will probably be the same ratio, if not worse...

So, try more batteries, or higher-current batteries?
I really appreciate your feedback Thanks a lot!
That was the precise issue I have last nite and could not understand the reason!
The situation with robots tanks must much worse and actually, the robot was on carpet...

The robot moves fairly fast straight but not turning at all! What was happening?
Since the robot is quite heavy carrying 6 new AA alkalines. I made an attempt to remove two of the batteries (so less weight) but same story, it doesn't want to turn.

Please, what batteries would meet your the "higher-current batteries" requirement?
I don't really wish to add more alkalines there because as I said before, the robot is quite heavy now.
Any idea?

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joan
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Re: A+ killed by a L298N

Fri Feb 13, 2015 5:53 pm

I guess you are stopping one motor to make the tank turn. That means you have to work against the friction of the other track.

Use PWM to slow rather than stop one motor. I guess it'll then turn OK.

Ravenous
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Re: A+ killed by a L298N

Fri Feb 13, 2015 5:57 pm

Maybe you could try Ni-Mh cells instead... They're only 1.2V each but they seem to deliver higher currents. (Beware of short circuits, you can burn the insulation off the cable.) And keep the weight down as much as possible.

I should point out mine is very different to yours, mechanically. (I originally intended to build a mini coffee table!) Probably weighs 3-4 Kg and runs off 12V Ni-Mh batteries and these motors:
http://www.robot-electronics.co.uk/htm/emg30.htm

It currently has two of these motors, one per side. At its heaviest it had four of them, two per side - but when heavily loaded, the wheels dug in at the corners when turning and lifted up the rugs! A nuisance. I think two wheels, one per side, is more practical indoors.

(I should also point out it is still running off an Arduino. I will fit a raspi board but haven't got that far yet. I guess that makes me a traitor!)

...But stick with your existing chassis and try more cells or slightly better (NiMh?) batteries first, or you will end up like me, with a very expensive doorstop! :oops:

rocinante
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Re: A+ killed by a L298N

Fri Feb 13, 2015 6:34 pm

Ravenous wrote:Maybe you could try Ni-Mh cells instead... They're only 1.2V each but they seem to deliver higher currents. (Beware of short circuits, you can burn the insulation off the cable.) And keep the weight down as much as possible.

I should point out mine is very different to yours, mechanically. (I originally intended to build a mini coffee table!) Probably weighs 3-4 Kg and runs off 12V Ni-Mh batteries and these motors:
http://www.robot-electronics.co.uk/htm/emg30.htm

It currently has two of these motors, one per side. At its heaviest it had four of them, two per side - but when heavily loaded, the wheels dug in at the corners when turning and lifted up the rugs! A nuisance. I think two wheels, one per side, is more practical indoors.

(I should also point out it is still running off an Arduino. I will fit a raspi board but haven't got that far yet. I guess that makes me a traitor!)

...But stick with your existing chassis and try more cells or slightly better (NiMh?) batteries first, or you will end up like me, with a very expensive doorstop! :oops:
uffff....this is getting more complicate than I initially thought. So much difference if I use NiMh?
I have 3 9Vbatteries at home...what about if I add them in parallel? Crazy?

gordon77
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Re: A+ killed by a L298N

Fri Feb 13, 2015 6:42 pm

joan wrote:I guess you are stopping one motor to make the tank turn. That means you have to work against the friction of the other track.

Use PWM to slow rather than stop one motor. I guess it'll then turn OK.
Couldn't you reverse the other motor when turning ?

rocinante
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Re: A+ killed by a L298N

Fri Feb 13, 2015 6:46 pm

gordon77 wrote:
joan wrote:I guess you are stopping one motor to make the tank turn. That means you have to work against the friction of the other track.

Use PWM to slow rather than stop one motor. I guess it'll then turn OK.
Couldn't you reverse the other motor when turning ?
I am actually doing that (both motors on in opposite direction) and it is not really helping.

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joan
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Re: A+ killed by a L298N

Fri Feb 13, 2015 6:55 pm

gordon77 wrote:
joan wrote:I guess you are stopping one motor to make the tank turn. That means you have to work against the friction of the other track.

Use PWM to slow rather than stop one motor. I guess it'll then turn OK.
Couldn't you reverse the other motor when turning ?
Overtaken by posts. I guess not. Perhaps the tracks are too long.

I'd go for differential speeds with PWM.

rocinante
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Re: A+ killed by a L298N

Fri Feb 13, 2015 7:54 pm

joan wrote:
gordon77 wrote:
joan wrote:I guess you are stopping one motor to make the tank turn. That means you have to work against the friction of the other track.

Use PWM to slow rather than stop one motor. I guess it'll then turn OK.
Couldn't you reverse the other motor when turning ?
Overtaken by posts. I guess not. Perhaps the tracks are too long.

I'd go for differential speeds with PWM.
Joan,

Assume my robot is an idle position. If I want to turn my robot 90 degrees PWM wont make a difference.
You think the same?

My initial idea was motor1 on and motor on (reverse)...

plugwash
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Re: A+ killed by a L298N

Fri Feb 13, 2015 8:08 pm

While a "tank style" chassis can turn on the spot doing so requires a very high level of sideways slip in the tracks. On a high friction surface this requires a LOT more torque than driving in a straight line or making gentle turns.

rocinante
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Re: A+ killed by a L298N

Sat Feb 14, 2015 8:37 am

Guys,

I am very surprised:

I have just exchanged the L298N bridge for a couple of relays and I can say the motor has a EXCESS of power!.
Of course, my tank is turning without any issue at all. Actually it turns very fast....I can even add lots more weight.

After this experience, my opinion is the L298n is completely useless. It consumes so much power it is pointless to use for small robots. Any feedback would be appreciated. Perhaps you have other cheap magic bridge?

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joan
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Re: A+ killed by a L298N

Sat Feb 14, 2015 8:46 am

rocinante wrote:Guys,

I am very surprised:

I have just exchanged the L298N bridge for a couple of relays and I can say the motor has a EXCESS of power!.
Of course, my tank is turning without any issue at all. Actually it turns very fast....I can even add lots more weight.

After this experience, my opinion is the L298n is completely useless. It consumes so much power it is pointless to use for small robots. Any feedback would be appreciated. Perhaps you have other cheap magic bridge?
The L298N does not waste much power. Show us a photo of your set up with the L298N.

If you are putting more than the couple of amps the L298N will supply to those motors I doubt they'll last long. What are they rated for?

rocinante
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Re: A+ killed by a L298N

Sat Feb 14, 2015 8:51 am

Hey Joan,

Check my diagram in the first post. I am using a 2x3V motors.
You right saying the motors will not last for long since I am using 6x1.5V batteries but with the L298N, the robot even doesn't want to turn! I dont really care about the motors. I really trust that I can even get rid of a couple of batteries.

What's the point to have the L298N? ok..motors wont reverse...but I dont mind that.

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joan
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Re: A+ killed by a L298N

Sat Feb 14, 2015 8:58 am

rocinante wrote:Hey Joan,

Check my diagram in the first post. I am using a 2x3V motors.
You right saying the motors will not last for long since I am using 6x1.5V batteries but with the L298N, the robot even doesn't want to turn! I dont really care about the motors. I really trust that I can even get rid of a couple of batteries.

What's the point to have the L298N? ok..motors wont reverse...but I dont mind that.
The diagram shows what you think you have done. A photo shows us what you have done.

rocinante
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Re: A+ killed by a L298N

Sat Feb 14, 2015 7:55 pm

Joan,

I have no longer the L298N installed. I am using 2 simple relays now with 3x1.5V batteries.
(no reverse)

Also I have just noticed this:
http://www.kuuco.com/images/propic/090433_Y14.jpg
http://raspimart.co.uk/wp-content/uploa ... oard-3.jpg

Please note the 12V and 5V inputs...what version is supposed to be the correct? I was using the second one.



GND L298N to GND raspberry.
9V + to

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joan
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Re: A+ killed by a L298N

Sat Feb 14, 2015 8:01 pm

All my boards are like the raspimart. There should be a label near the terminals on the edge of the board.

gordon77
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Re: A+ killed by a L298N

Sat Feb 14, 2015 8:03 pm

Some people connect the 5v from the Pi, some don't, whats the 5v for?

rocinante
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Re: A+ killed by a L298N

Sat Feb 14, 2015 8:08 pm

gordon77 wrote:Some people connect the 5v from the Pi, some don't, whats the 5v for?
Explanation here:
5v input (unnecessary if your power source is 7v-35v, if the power source is 7v-35v then it can act as a 5v out)

rocinante
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Re: A+ killed by a L298N

Sat Feb 14, 2015 8:12 pm

joan wrote:All my boards are like the raspimart. There should be a label near the terminals on the edge of the board.
Mine also. I have the +12V label in the left side of the board(6x1.5V batteries) By the way, my L298N gives me 8.5V (without motor) in the out1 or out2. I think the board is eating most of the current. So motors cannot move when they have a significant load.

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