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[DPRG] RE: Re: Motor Control and parts shopping

Subject: [DPRG] RE: Re: Motor Control and parts shopping
From: Paul Bouchier bouchier at classicnet.net
Date: Sun Aug 30 16:07:31 CDT 2009

Gary - think hard before you go the tracked route. You can't use encoders to
tell how far you've turned - you virtually have to use a compass (which
brings magnetic susceptibility) or an IMU or more exotic techniques. Even
straight-line dead-reckoning is harder, because you don't know how many
degrees the robot turned when the left track ran ahead 100 counts, or
whether it will turn the same amount back when you run the right track to
catch up. Speed isn't the issue - it's dead reckoning accuracy.

-----Original Message-----
From: dprglist-bounces at dprg.org [mailto:dprglist-bounces at dprg.org] On Behalf
Of Gary Burton
Sent: Saturday, August 29, 2009 7:47 PM
To: dprglist at dprg.org
Subject: Re: [DPRG] RE: Re: Motor Control and parts shopping

I'm still going to go to with the L293D for right now. It's tried, tested
and has a minimum of parts. The voltage needed for the motors is well within
it's range. There is an upgrade path for both chip and motors. Plus the fact
the programming for it is quite simple. I'd prefer to use steppers or
gearheads, instead of geared down cheap variable DC motors. I'd also like to
get it moving and move on to encoding the drive shafts and working on the
sensors. This is my first bot, so vast improvement may seem built in and I'm
taking notes on the next one which should be a vast improvement.
So far Leo will have tracked drive driven by geared down DC motors from a
L293D, bumper sensors and IR sensors for object finding at range all
controlled by an AtMega328.  Wheels might be faster, steppers would probably
be more efficient with the proper board to drive them and either a few ARM
modules or a few networked At328 chips would be preferred. Baby steps is a
good thing and makes debugging for somebody who's not done this
succcessfully before, much easier. 
Hopefully, soon I'm using the stuff like you guys probably are, but till
then bear with my simplistic and naive decisions.

On Fri, Aug 28, 2009 at 3:14 PM, Jose I Quinones <jiq at avayan.com> wrote:

You would think it is like a Servo controller, but that is in fact a miss
conception. I am writing a tutorial depicting the differences between RC PWM
and Speed Control PWM.


But basically, RC PWM encodes the position information on  a pulse that is
1.0 ms to 2.0 ms wide with 1.5 ms encoding dead center (if properly


With Speed Control PWM, there is no information encoded. What you are doing
is segmenting the available energy into percentages. Per example, if you
have a 12V battery, a PWM on the ENABLE or the PHASE pin translate into how
much time the motor is ON and how much it is OFF, which is equivalent to a
fraction of the 12V. Hence, a 50% duty cycle PWM with a 12V battery is
analogous to a 6V battery. That is why you can use this to control motor
speed. Because speed is directionally proportional to applied voltage. You
can see this better on a video I released last week. I expect to present
more videos in the upcoming weeks, in case you are interested in motion
control basics.






From: Jose I Quinones [mailto:jiq at avayan.com] 

Sent: Friday, August 28, 2009 1:27 PM
To: 'dprglist at dprg.org'

Subject: Re: Motor Control and parts shopping 


Hi guys!


Allow me to recommend something totally different and to my understanding
considerably easier to use, better deal, and better performance. Maybe it is
"less fun" but I believe it can still be an enjoyable experience.


TI has a new device called the DRV8800PWP. It is a 2.8A H Bridge. The cool
thing about is that all you need to supply is ENABLE and PHASE. So you do
not have to worry about all the IN1/IN2 combinations, decay modes and stuff.
Just to add to the coolness, it is protected against output shorts, thermal
overrun and demonic possessions. This thing is practically immortal! The
only thing that it will not survive is voltage inversion or over voltage but
I have hardly heard of an H Bridge that contains those features. I believe
we are supposed to be minded enough to not let something as simple to


That being said, you can PWM either the ENABLE or the PHASE and you get
speed control on both situations. You may be saying "WHAT THE HECK??? PWM
THE PHASE?" If you have never heard of this, it allows you to control both
direction and speed with a single PWM timer. Per example, if PWM duty cycle
(DC%) is less than 50%, then the motor moves Counterclockwise (CCW). The
closer the DC% is to 0%, the faster the motor moves. But if DC% is above 50%
then the motor moves clockwise (CW). In this case, the closer the DC% is to
100%, the faster the motor moves. This is of course only possible when
ENABLE is asserted.


I have a design on my Open Source Design web page around this chip and am
working some new versions. Feel free to take a look and copy whatever you
want. It is as free as free gets. I also have some bare boards to sell in
case you want to build your own. They are sold at whatever cost me, so in
other words as cheap as I can afford.


BTW if you need superbly high currents (which does not seem to be the case
for those considering to use a 600 mA device), then there is another larger
design here:


Thanks and best regards,




Feel free to visit some of my pages at:

http://www.avayan.com <http://www.avayan.com/> 

http://avayanings.blogspot.com <http://avayanings.blogspot.com/> 

http://www.comicups.com <http://www.comicups.com/> 


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