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Posted by Albert Goodwill on September 6, 2008, 9:40 am
Hey,
I need expert advise !!!
I am planning to build a robotic rover with 6 wheels. Rover will be
able to carry approximately 10kg load.
Each wheel will be driven by a separate small DC servo motor with
quadrature encoder.
Heading angle of 4 of these motors will be controlled by separate
motors. Therefore there will be 10 motors to drive wheels.
Note that, these motors are NOT radio control (RC) motors.
Following links shows the source of my inspiration;
http://ksjtracker.mit.edu/wp-content/uploads/2008/02/marssciencelab.jpg
http://ridwan.chendarma.com/v/project/
http://www.emeraldinsight.com/fig/0490340205001.png
Can you advise me on the following
* Where can I find low-cost small DC motors with quadrature
encoders?
* Where can I find servo motor controller for these 10 motors? (I
want to be able to control these motors in velocity and position mode.
Therefore I am looking for some kind of of PID controllers)?
* Do you know any rover mechanical CAD design files on internet?
Thank you.
Albert Goodwill
albertgoodwill @ gmail com
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Posted by on September 6, 2008, 10:44 am
Albert Goodwill wrote:
> Hey,
>
> I need expert advise !!!
>
> I am planning to build a robotic rover with 6 wheels. Rover will be
> able to carry approximately 10kg load.
> Each wheel will be driven by a separate small DC servo motor with
> quadrature encoder.
> Heading angle of 4 of these motors will be controlled by separate
> motors. Therefore there will be 10 motors to drive wheels.
> Note that, these motors are NOT radio control (RC) motors.
>
> Following links shows the source of my inspiration;
> http://ksjtracker.mit.edu/wp-content/uploads/2008/02/marssciencelab.jpg
> http://ridwan.chendarma.com/v/project/
> http://www.emeraldinsight.com/fig/0490340205001.png
>
> Can you advise me on the following
> * Where can I find low-cost small DC motors with quadrature
> encoders?
> * Where can I find servo motor controller for these 10 motors? (I
> want to be able to control these motors in velocity and position mode.
> Therefore I am looking for some kind of of PID controllers)?
> * Do you know any rover mechanical CAD design files on internet?
>
> Thank you.
>
> Albert Goodwill
> albertgoodwill @ gmail com
I can't give expert advice, but it sounds like you need 10 DC gearmotors
with encoders, 10 motor drivers (the amplifier electronics), and a
microprocessor to direct the motor drivers. The microprocessor can easily
drive the motors with a PWM signal, although you'll have to search for one
with 6 timers. The problem I see is when you say "low cost". You might be
able to get the motors in a surplus shop, but with encoders they will still
probably be $30 to $50 US each (if you're lucky). Motor drive amplifiers
will probably have to be new, and they are $30 to $100 US, each. With
structure and everything else, you're probably looking at $1000US. Does
that meet your definition of "low cost"?
Also, encoders don't do velocity all that well, the microprocessor has to
compute it and noisy values result, which may have to be averaged,
introducing a time lag in the data. A tachometer gives better velocity
sensing, but isn't that great for positioning.
You'll scale back the cost a bunch if you just use 4 wheels. Once it is
working, you could add the other two wheels if your requirements and budget
dictate so.
Here's a good place for micros and drive amplifiers:
http://www.bdmicro.com/
I've used several of their products, and they provide great technical help
during the build. The AVR ATmega128 processor has plenty of computation
power for servo loops (but only 4 timers). It also has good Linux support,
which was important to me.
There are also serial servo controllers that can issue PWM commands to many
motor drivers, the processor commands it over a single RS-232 line.
I think the Mars Rover double-bogie design is available on the net, but I
don't have any pointers.
Mike Ross
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Posted by cadcoke4 on September 6, 2008, 1:26 pm
Sorry, no wheel help here. But, for CAD files, I suspect that if you
contact the people at one of the links you provided , they may have
some CAD Files.
Joe Dunfee
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Posted by RMDumse on September 7, 2008, 12:17 pm
> * Where can I find servo motor controller for these 10 motors? (I
> want to be able to control these motors in velocity and position mode.
> Therefore I am looking for some kind of of PID controllers)?
You might want to look at our IsoPod(TM) and ServoPod(TM) line.
With a single one of those boards, you can have up to 6 hardware
quadrature inputs, and either 6 complementary PWM outputs, or 12
independent (single line) LAP PWM outputs. If your four steering
motors were analog feedback, rather than quadrature, you'd have enough
quadrature and PWM to drive the whole robot off of a single processor
board, with PID and position/velocity control on all.
Randy M. Dumse
www.newmicros.com
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Posted by Albert Goodwill on September 8, 2008, 6:46 am
> > * Where can I find servo motor controller for these 10 motors? (I
> > want to be able to control these motors in velocity and position mode.
> > Therefore I am looking for some kind of of PID controllers)?
> You might want to look at our IsoPod(TM) and ServoPod(TM) line.
> With a single one of those boards, you can have up to 6 hardware
> quadrature inputs, and either 6 complementary PWM outputs, or 12
> independent (single line) LAP PWM outputs. If your four steering
> motors were analog feedback, rather than quadrature, you'd have enough
> quadrature and PWM to drive the whole robot off of a single processor
> board, with PID and position/velocity control on all.
> Randy M. Dumsewww.newmicros.com
Dear Randy,
Thank you for the information.
I have just checked your web site with for your IsoPod(TM) and
ServoPod(TM) product line.
They sound FANTASTIC!!!
However, they seem to have 2 quadrature encoder inputs rather than 6.
Am I missing something here? Can you tell me how to connect 6
quadrature encoders?
Can IsoMax (Virtually Parallel Machine Architecture Programming
Language for IsoPod(TM), ServoPod(TM)) handle 10 PID concurrently (6
with quadrature encoder feedback and 4 with analog feedback)?
Your NMIH-0030 H-Bridge product (10 of those) also seems to be
suitable for my application. I assume that in addition to 10 PWM
signals, IsoPod(TM) and ServoPod(TM) can also concurrently produce Dir
(direction)
signals. (Can you confirm this please?)
Is it also possible on to decode multiple channel RC pulse streams
(see http://www.veetail.com/HowRCworks3.shtml ) with IsoPod(TM) and
ServoPod(TM)?
Thank you
Albert Goodwill
albertgoodwill at gmail com
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>
> I need expert advise !!!
>
> I am planning to build a robotic rover with 6 wheels. Rover will be
> able to carry approximately 10kg load.
> Each wheel will be driven by a separate small DC servo motor with
> quadrature encoder.
> Heading angle of 4 of these motors will be controlled by separate
> motors. Therefore there will be 10 motors to drive wheels.
> Note that, these motors are NOT radio control (RC) motors.
>
> Following links shows the source of my inspiration;
> http://ksjtracker.mit.edu/wp-content/uploads/2008/02/marssciencelab.jpg
> http://ridwan.chendarma.com/v/project/
> http://www.emeraldinsight.com/fig/0490340205001.png
>
> Can you advise me on the following
> * Where can I find low-cost small DC motors with quadrature
> encoders?
> * Where can I find servo motor controller for these 10 motors? (I
> want to be able to control these motors in velocity and position mode.
> Therefore I am looking for some kind of of PID controllers)?
> * Do you know any rover mechanical CAD design files on internet?
>
> Thank you.
>
> Albert Goodwill
> albertgoodwill @ gmail com