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Author Topic: DC motor polarity changer. Spec in detail inside.  (Read 1996 times)

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Offline jop_balTopic starter

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DC motor polarity changer. Spec in detail inside.
« on: February 10, 2011, 12:26:05 AM »
err.... I am a layman. I am trying to design the following.

A hand held battery operated simple blade cutting lawn mower for farm use.

I have a 20K rpm DC motor @ no load operating with a 9V rechargeable battery.
A PWM circuit that is used for changing the speed.

Now, I need this motor to reverse the direction when it is struck(i.e. when rpm falls to zero) due to the load.

Note: I am not eager to measure the rpm. All I need is, if the motor does not run in one direction change the polarity, so that it strikes grass from the other direction.
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Offline rbtying

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Re: DC motor polarity changer. Spec in detail inside.
« Reply #1 on: February 10, 2011, 12:33:52 AM »
Use a current sensor on the motor leads, and reverse when nearing the motor's stall current.
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Offline jop_balTopic starter

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Re: DC motor polarity changer. Spec in detail inside.
« Reply #2 on: February 10, 2011, 01:05:38 AM »
How do I do it?
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Offline newInRobotics

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Re: DC motor polarity changer. Spec in detail inside.
« Reply #3 on: February 10, 2011, 02:02:21 AM »
I'm not sure how to achieve it because I've never used one before; but have a look at this Wiki and this SoR page :)
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