Subject:
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Re: High current motors
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Fri, 5 Apr 1996 00:11:32 GMT
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Original-From:
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David Negro <dln2@cornell.{AntiSpam}edu>
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Viewed:
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2191 times
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I think the question on how to run higher current motors has got to be the
most asked question here. Maybe we should add more info to the FAQ or
something. Anyway, here is Chuck McManis' solution from a while back. I
hate to send out something that a bunch of us have already seen... but some
people obviously aren't checking the web first.
-dave
Follows is a design for a H-bridge by Chuck McManis that I
have not personally implemented.
-------------------------------------------------------------
There is no recommended way. I've got a pretty simple bipolar
H-bridge design that you can connect up pretty easily using an
opto isolator and get 3 - 6amps of control and software compatibility.
Unfortunately I'm not in the kit business nor do I have the time to
put together a wonderful package like the ones Fred does. This works
great on the miniboard, I've not checked the HB docs so Fred correct
me if the motor connector operation is not the same.
Allow me to describe it and if you can solder you should be able
to build it:
The motor connector has three pins they are actually Motor A, V+,
Motor B. Normally they are all at V+ when the motor is "off" (the
motor is simply monitoring the difference between Motor A and
Motor B. When you "turn on" the motor either Motor A or Motor B
(depending on direction) goes to ground potential, and the motor
sees the voltage difference and runs.
You can build a common collector H-bridge using TIP120 and TIP125
darlington power transistors. The bridge is built by connecting the
emitters of the PNP transistors to the motor supply, connect the
collectors of one pair together and to one terminal of the motor,
and connect the collectors of the other pair together and to the
other motor terminal. Connect the emitters of the two NPN
transistors to ground. Put diodes (I us 1N4001's but you can use
anything that is rated > 10amps surge) connected between the
collectors and emitters of each power transistor, making sure
they are reverse biased (that is the banded end connects closer to
the V+ supply than the other end)
They should be configured sort of like this:
V+
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+------------------+
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Q1+-+ +-+ Q2
------O ^ D1 D2 ^ O-----
+-+ +-+
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+--- Motor ----+
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Q3 +-+ +-+ Q4
------O ^ D3 D4 ^ O-----
+-+ +-+
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+-------+----------+
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Ground
Q1 and Q2 are PNP, Q3 and Q4 are NPN, D1 thru D4 are the diodes.
Now connect the emitter of one 2N2907 to the base of Q1, connect
the emitter of the 2907 to a 180 ohm resistor and then connect
the resistor to the base input of Q4. Do the same thing with
another 2N2907 connecting the base of Q2 to the base of Q3 through
a 180 ohm resistor. Now connect an opto isolator to the motor drive
as follows. Connect two of the internal LED cathodes to the middle
pin of the motor connector. Connect the cathodes of the LEDs through
a 330 - 470 ohm resistor one each to motor A and motor B of that
connector. Now on the transistor side of the optoisolator. Connect
the collectors of the affected transistors to a 1K resistor and then
to the V+ motor supply. Connect the emitters of these transistors
to ground. Now where the 1K resistors connect to the optoisoloater
transistor collecters connect them also (one each) to the base
of the 2n2907's.
The way it works is as follows:
The motor driver (L293D) turns "on" by grounding either
Motor A or Motor B, this causes the LED in the optoisolator
to illuminate. Which turns on the associated transistor in
the optoisolator. The optoisolator transistor turns on and
connects the base of the appropriate 2n2907 to ground which
turns on the 2n2907. Current then flows through the 2n2907
which pulls down the base of the PNP transistor is connected
to and pulls up the base of the NPN transistor. These two
transistors turn on and current flows through the motor.
The added advantage here is that the motor supply on the external
H-bridge can be much higher and separate from the supply on the
Handy board. Thus you can run 48v motors for example.
Sorry I can't do better graphics on short notice.
--Chuck
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Message has 1 Reply:
 | | Re: High current motors
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| (...) On the handy board, this is different, isn't it? I didn't think that the center pin was V+... In fact, isn't it not a connection at all? (...) Isn't this supposed to read, "Now connect the COLLECTOR of one 2N2907 to the base of Q1, connect the (...) (29 years ago, 15-Apr-96, to lugnet.robotics.handyboard)
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