Author Topic: PWM ideas  (Read 917 times)

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Offline robo mikeTopic starter

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PWM ideas
« on: November 11, 2010, 04:22:39 PM »
Hello all,
I am building a contraption powered by a electric screwdriver motor. I want to make a speed controller for it.  Could anyone point me towards a simple (im not terribly tech savy!) PWM schematic.  The motor is 3.6v, 0.8a. 

Cheers!

Offline Soeren

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Re: PWM ideas
« Reply #1 on: November 11, 2010, 04:27:34 PM »
Hi,

A 555 with a power transistor at the output should do.
Here is a lot to look at.

Regards,
Søren

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Offline Spoil9

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Re: PWM ideas
« Reply #2 on: November 12, 2010, 10:48:08 AM »
Not sure on your skill level (not tech savy?) but in my own research for speed controllers and motor controllers I found this website that helps break it all down for you.

The PWM starts at step 7 and below but I recommend reading the whole page to get a good overview of everything.

- Will
Knowledge is Power. Power Corrupts. Study Hard. Be Evil.

Offline robo mikeTopic starter

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Re: PWM ideas
« Reply #3 on: November 12, 2010, 11:38:58 AM »
Hmmm yup, I think i might try the 555 one.  Lots of PWM kits you can buy are for 12v so this one should be a better bet.  It should be able to handle 0.8amp (or better at least 1amp to be on the safe side!) right?...

Offline Soeren

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Re: PWM ideas
« Reply #4 on: November 13, 2010, 02:41:54 PM »
Hmmm yup, I think i might try the 555 one.  Lots of PWM kits you can buy are for 12v so this one should be a better bet.  It should be able to handle 0.8amp (or better at least 1amp to be on the safe side!) right?...

Yes, you could use this schematic, it will handle this and then some.
If you cannot get TIP31, TIP41 or any similar power transistor will do.
The chip should be the CMOS variety (LMC555, LM555C, 7555 etc) to ensure drive from 3.6V

Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline robo mikeTopic starter

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Re: PWM ideas
« Reply #5 on: November 14, 2010, 04:30:16 AM »
fantastic!  Thanks soeren  :-*

Offline robo mikeTopic starter

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Re: PWM ideas
« Reply #6 on: November 22, 2010, 02:42:13 PM »
Oh one last thing...

The electric screwdriver I got the motor out of had a resistor in series (on the negative I think).  It was too damaged by over heatedness to see what value it was.  Was it there to protect the motor from the power adaptor?  Or maybe the power adaptor from induction from the motor?! 
What I was wondering was do I need to replace it?  If so how do I work out the value and where would it go on the previously recomended 555 circuit?

(in case its any use im going to be powering the motor from a 3.5v, 1a adaptor to match the motor)

Appologies for my naivety, you are all very kind.

Offline Soeren

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Re: PWM ideas
« Reply #7 on: November 22, 2010, 05:25:10 PM »
Hi,

The electric screwdriver I got the motor out of had a resistor in series (on the negative I think).  It was too damaged by over heatedness to see what value it was.
If the heat hasn't changed the value, you could measure it.
It doesn't matter what side it was connected to.


Was it there to protect the motor from the power adaptor?  Or maybe the power adaptor from induction from the motor?! 
What I was wondering was do I need to replace it?  If so how do I work out the value and where would it go on the previously recomended 555 circuit?
The most likely reason for a resistor in series with the motor in a screwdriver would probably be to protect the motor and/or the driver against too high currents if stalled on a  screw that won't budge.
Another possible reason could be to adapt a lower voltage motor to the battery.

With the 3.5V supply and the PWM, you may easily test, with increasing PWM output (say 1/4 the scale each step), if the motor gets hotter than you can hold it (around 50°C) a small value resistor may be needed (or the circuit could be rearranged to have a lower power max. output).

When you have the circuit ready and hooked up, just drop me a PM if you need more specific guidance.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

 


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