Society of Robots - Robot Forum
Electronics => Electronics => Topic started by: Jak24 on October 30, 2010, 05:33:32 AM
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Hi!
I just recently realized that the reason that my robot is slower than calculated, could be the voltage loss in the l298n.
I am using a 12v battery to power a (3)12v motors, and turns out the l298n gives the motor only 10.8 , so the loss is 1.2 v.
When my battery is fully charged (13,8 v) then it gives 12.6,
my question is:
Is there any way to get rid of the voltage loss, is there a better h-bridge chip, or are they all pretty much the same?
Thanks
Regards
Jak24
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The LMD18200 H-bridge is what you are looking for. It uses MOSFETs so it doesn't get really hot like the L298 (which uses bi-polar transistors and provides a significant voltage drop to the motor). It also has built in flyback diodes, so you don't need external diodes like with the L298. The disadvantage is that there is only 1 H-bridge per package, whereas the L298 has 2 (a dual H-bridge). This makes the L298 cheaper to use.
Also 1V do you actually thank that will make a difference. Did your calculations take into account weight, fraction and that the rated RPM of your motors is for no load , so under load they will drop a considerably amount like 20-30%.
:P
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Hi,
I just recently realized that the reason that my robot is slower than calculated, could be the voltage loss in the l298n.
Easy to test - wire one of the motors around the L298 (i.e. let it get full speed) and compare.
However... Calculating the exact top speed of a vehicle is next to impossible unless ALL factors are known.
Is there any way to get rid of the voltage loss, is there a better h-bridge chip, or are they all pretty much the same?
There are lots of better bridges, but did you consider a relay and a single power MOSFET per motor?
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Hi!
The LMD18200 H-bridge is what you are looking for. It uses MOSFETs so it doesn't get really hot like the L298 (which uses bi-polar transistors and provides a significant voltage drop to the motor). It also has built in flyback diodes, so you don't need external diodes like with the L298. The disadvantage is that there is only 1 H-bridge per package, whereas the L298 has 2 (a dual H-bridge). This makes the L298 cheaper to use.
Also 1V do you actually thank that will make a difference. Did your calculations take into account weight, fraction and that the rated RPM of your motors is for no load , so under load they will drop a considerably amount like 20-30%.
:P
Yeah that h-bridge might be a better consideration.
Hi,
I just recently realized that the reason that my robot is slower than calculated, could be the voltage loss in the l298n.
Easy to test - wire one of the motors around the L298 (i.e. let it get full speed) and compare.
I tested it like that, i got about 15% more speed
However... Calculating the exact top speed of a vehicle is next to impossible unless ALL factors are known.
Yeah, when i did my calculations I only considered the main factors, and i didn't consider things like:
loss in friction, losses in motor (as it doesn't always preform the nominal speed/torque) etc...
Is there any way to get rid of the voltage loss, is there a better h-bridge chip, or are they all pretty much the same?
There are lots of better bridges, but did you consider a relay and a single power MOSFET per motor?
wouldn't that only allow the motor to turn in one direction?
Thanks
Regards
Jak24
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Hi,
I tested it like that, i got about 15% more speed
Oh, then it's surely worth going for a better solution.
There are lots of better bridges, but did you consider a relay and a single power MOSFET per motor?
wouldn't that only allow the motor to turn in one direction?
No, the relay controls the direction and the MOSFET controls the speed.
Here (http://That.Homepage.dk/PDF/PWM+Relay_4_Motor_Ctrl.pdf) is a circuit I've posted before.