[TriEmbed] Voltage regulation for battery driven mobile robots

Mon Jan 20 11:29:00 CST 2014

A couple of thoughts:
* You can easily power the Teensy via the RPi pins if it is only the Teensy
and nothing beyond that.  I power both a sensor board with a couple I2C
devices I power directly off of the RPi pins (3,3v) and an Arduino (5v), as
well as a few LEDs, directly off of the RPi power pins on P1.  I don't know
what the maximum power rating through that connector, but it is enough for
just the Teensy.

* While you can use the same battery for both your electronics and your
motor, you may have problems with power spikes from the motor being fed
back into your other electronics and causing issues.  If you have the space
and weight rating for a second battery, I would definitely recommend that.

* For powering the RPi, I have found that the external cell phone chargers
make excellent battery packs.  They are lightweight, and most have a power
on/off button and power on light built in and they can power the RPi for
hours.  I have a 5000mah unit that I use for 5+ hours without an issue, and
Ruth Suehle (of the RPI Hacks book) has reported she uses a 12000mah unit
for 12+ hours.  You have USB power out and you can use a short USB power
cable to power the RPi, and then use the RPi to power the Teensy and a few
other sensors - so all your electronics will be one rechargeable pack.  You
don't even need to remove the pack to charge it as it has it's own charge
plug in the side.  This is what I have used on my nearspace balloon
project, plus a few other RPi test projects. Here is one as an example of
the battery pack:

http://www.amazon.com/Poweradd-trade-Pilot-Dual-Port-Blackberry/dp/B00B688RZA/ref=sr_1_5?s=wireless&ie=UTF8&qid=1390237990&sr=1-5&keywords=5000+mah+battery
)

* For the WiFI dongle, you *may* be able to get away with powering it
directly from the RPi.  Many have reported a problem, but others have
reported it working.  The number of permutations of WiFi dongles and the
old/new RPi design make it hard to completely say yes or no.  However, if
you are already using the cell phone battery pack, you usually get 2 USB
power ports on it.  So use a Y connector where your WiFI dongle pulls power
from the battery pack, but still gets it's control signals from the RPi.
 This was also used in my nearspace balloon project.  Here is an example:

http://www.amazon.com/Apricorn-Power-Adapter-Cable-AUSB-Y/dp/B000JIOHDE/ref=sr_1_1?s=pc&ie=UTF8&qid=1390238076&sr=1-1&keywords=short+usb+y+power+cable

* You mention using a webcam.  If it is connected directly to the RPi, I
would definitely swap out the webcam for the RPi camera - it is lighter
weight, lower power, easier to control, and you get better
resolution/quality photos than with a webcam.

* So if you use the cell phone charger for the RPi and other electronics,
you could then power the motors from a standard 7.2v power pack and use the
7.2v -> 6v regulator that Scott mentioned. This will keep the two power
supplies separate and will help with the motors.  You could probably drive
the motors directly from the battery pack, but the only issue is that by
not using regulated power, you will notice that the robot wheels will move
slower as the batteries start to discharge.  Depending on your use, this
may or may not be an issue to you.

* I am not 100% sure the ultrasonics will work if powered by the RPi - I
think it will work, but it could cause problems for the same reasons I
would not share the power with the motors.  The ultrasonic pulses are not
bad and can be easily powered by most controllers, but it comes down to how
much power can be pulled from the RPi.  I would have no problem suggesting
you try it, and if it does not work, you will need to pull that power from
somewhere else.

* I have also used some of the smaller switching power supplies on robotic
systems as well, and they do work well - just be careful of keeping motors
and other electronics separate.

* If you have to connect the grounds of the motors and other electronics
together, consider using a small inductor as the ground connect between the
two supplies to help decouple the spikes.

* Place caps across the motor leads to help keep the transients closer to
the motor and keep your motor wires short and away from other signals.

http://www.pololu.com/docs/0J15/9

Probably more ideas later - but that is a start...

On Mon, Jan 20, 2014 at 11:47 AM, Scott Hall <scottghall1 at gmail.com> wrote:

>  This is where we could benefit from the experience of the robotics club
> guys (TAR - Triangle Area Robotics).
>
> You will want to power the teensy on its own, not through the power pins
> on a R-Pi.
>
> Circuit Cellar Magazine last August & September published a Raspberry-Pi
> I/O board that is far superior to the Gert Board and its like, but its
> shares one basic element:
>
> They have their own power connector, and regulate that with a switching 5V
> regulator and a separate 3.3V regulator.  That latter they connect to pin-1
> of the GPIO connector to power the R-Pi - the USB power is never involved.
>
> If you are not using the 5V supply for anything beyond the motors,
> consider this 6V regulator instead (
> https://www.commonsenserc.com/product_info.php?products_id=51)  --
> that'll get you more torque out of your motors, and constant voltage
> regardless of the battery level.
>
>

> On 01/20/2014 12:14 AM, Charles West wrote:
>
>   Hello,
>
>  I'm building a mobile robot from an RC tank.  I'm hoping to have a
> Raspberry Pi with a Webcam, Wifi dongle and speakers for the top layer,
> connected via USB to a Teensy 3.0 board (3.3 volts), which will be doing
> PWM with 2 H-bridges to control the motors and feeding back data from 3
> HC-SR04 ultrasonic sensors (5 volts).
>
>  The motors/batteries are suppose to be at 6 volts.  I think I could
> boost that to as high as 9 volts without problems (though it will oscillate
> as the motors are used).
>
>  The Teensy can be powered from USB from the Raspberry Pi and will just be
> switching transistors (so the current draw shouldn't be much).  It looks
> like most everything else besides the motors will be running at 5 volts.  I
> could just use a linear regulator, but with the Raspberry Pi and
> accessories I think the wasted power could be substantial.
>
>  I could use a switching regulator, but the ones I've seen so far seem to
> need a lot of external components (this is mostly on breadboard at this
> point).  Do you guys tend to use complete PCBs (like this one:
> http://www.ebay.com/itm/171193232080)?
>
>  This is my first battery operated project, so I don't really know the
> common solution here.  If I may ask, what would you advise?
>
>  Thanks,
> Charlie West
>
>
> _______________________________________________
> Triangle, NC Embedded Computing mailing listTriEmbed at triembed.orghttp://mail.triembed.org/mailman/listinfo/triembed_triembed.org
> TriEmbed web site: http://TriEmbed.org
>
>
>
> --
> Scott G. Hall
> Raleigh, NC, USAScottGHall1 at GMail.Com
>
>
> _______________________________________________
> Triangle, NC Embedded Computing mailing list
> TriEmbed at triembed.org
> http://mail.triembed.org/mailman/listinfo/triembed_triembed.org
> TriEmbed web site: http://TriEmbed.org
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.triembed.org/pipermail/triembed_triembed.org/attachments/20140120/fbddb4b5/attachment.htm>