MOTOR RUN SLOW!?!?!

[alextan]

i use PIC controler to triggle my H-brigde for my motor......with +5V at Vcc and transistor input.....
its too slow compare that i apply +5v directly to the motor......
anyone can help me......
i dont know the motor specification because i get it from my old toy......

 

[polar bear6]

hmm, for me it sounds like the motor is bad, most toy motors are not efficient, try to get motors from portable walkmans and CD players, they usually have good motors.
you can also check the toy, use a multimeter to check the current and voltage on the motor when its wired to the toy.
i would have changed motor, since most toy motors are not that good.

[alextan]

but when connect the motor to the battery directly. it run quite fast.
when it pass through the PIC and H-bridge,its alow and only last for 9minute only.....
i use 4 1.2V 3800mAh battery....

[Admin]

Increase the pulse width of your PWM. the speed of your motor is directly related to PWM.

For a PIC, off the top of my head, i think you send from 0 to 1028, where that number directly determines pulse width. make sure you send it a long int and not an int, which maxes out at only 256.

[alextan]

i didnt use the PWM to control motor speed....i use the port B of PIC16F876A to give signal to the H-bridge so the +5V of Vcc can flow in the H-bridge and make the motor rotating.....
signal pattern is 1010 and 0101 so that the motor will rotate in clockwise and anti-clockwise...

 

[Admin]

ok, put a small time delay right after you call your pins high, and a different time delay when you make them low. so for example:

pwm(pins 1010) //pins high

delay_ms(5) //on delay

pwm(pins 0000) //pins low

delay_ms(1) //of delay

to control your motor speed, what you do is change the on/off time ratio.

for example, an on delay of 5ms and off of 0ms means it is on 100% of the time.

an on delay of 2ms and an off delay of 2ms will give you half speed.

If you arent using PWM and just have the pins high for several seconds, check with a multimeter the voltage going across your h-bridge mosfets and see what they give.

Also, if you are just using cheap toy motors, consider buying a motor driver IC, much easier to work with.

[alextan]

ok.....
but why it only last for 9 minutes ++ only.....

 

[Admin]

If you power restart the PIC, does it work again for 9 minutes or does not work anymore ever?

[alextan]

i use a rechargeable battery....
every time i use fully charged battery, it only run for 9minutes only...why?

 

[Admin]

Does the battery fully drain and you must recharge? How many mAh does your batteries have? How many cells?

And again, if you turn off then on your PIC, does it work again for 9 minutes?

[alextan]

i used 4 "AA" 1.2V 3800mAh. if i switch off and on it again. it can run more 1++ minutes.
the LED which show the power in circuit will blinking after 9++ minutes. so i think the battery is drain.

[Admin]

Ok this means your batteries are running low within 9++ minutes. But this is strange, because 3800mAh should give you around 4 hours of battery life with a 5V motor. Are you sure its 3800mAh? I didnt know they sold AA batteries above 2500mAh.

Hmmm do the batteries overheat? Does the MOSFET's on your circuit overheat? Check for shorts.

Are you sure you are fully charging your batteries? Are they NiMH or NiCAD? At 3800mAh with a NiMH, it will take about 13 hours to fully recharge with your typical 300mAh wall transformer battery charger. Are you sure they are fully recharged?

Otherwise, try recharging your batteries for 13 hours and see what happens.

[alextan]

sorry for late reply.....still busy with the power problem.....
yap...i'm sure its a 3800mAh and NiMH battery from sony....
it just take only 30 minutes to fully recharge it (seen the LED of charger turn off)
i had tried twice and the motor run for 9++ minute.
the weight should be no problem seen i had remove some part of the casing.
i buy a same, new tank so that the motor can perform better but the result is same.
the are no over heating in my circuit and the battery.

AAAARRRRRRRRRRRRR.......someone pls help me

[Admin]

hmmmm I am not sure.

Are you using a charger designed for NiMH batteries?

Perhaps a battery or two is damaged or is old and has trouble holding a charge?

And the motor doesnt overheat, right?

Not sure what else it could be . . .

[Ben]

You should note that there will be a slight voltage drop across the H-Bridge when it is connected.  Even if you use 100% duty cycle, you'll still get slightly less power delivered to the motor because of the inherant resistance of the H-bridge.  This means that the motor will not run as fast when connected through an H-bridge as it would connected directly to the battery! You may want to use a voltmeter to measure the voltage across the motor (forget pwm for this test and just turn the H-bridge on), and if its lower than you want you can always use a slightly higher voltage battery. I would guesstimate a 6V battery would do well for a 5V motor.  It depends on what H-bridge you're using.

As for the battery problem, you might consider charging the batteries, but connecting them to a "test circuit" with some sort of components like resistors and LEDs.  Then watch how long it takes to discharge the batteries.  Also, keep in mind that some motors can pull a TON of current.  I've got a miniature 1.2V motor for a toy airplane that pulls around 1A!  I've even heard of them pulling 3A or more.  Your motors could be using up a ton of power without you realizing it. Just a thought.