My project has ample batteries and I need to drive two servos under load. Can I simply connect my servo control lead directly to power source, then servo control lead to my uno?
I've seen servo drive shields and so forth, but rather avoid them if I don't need them.
FullOfBadIdeas:
My project has ample batteries and I need to drive two servos under load. Can I simply connect my servo power lead directly to power source, then servo control lead to my uno?I've seen servo drive shields and so forth, but rather avoid them if I don't need them.
Yes. Don't forget to connect the grounds on the two power supplies. And connect the servo grounds directly to the power source, so they don't go through the Uno.
Servo shields are useful to add extra PWM outputs, more than what the Uno has, and they also have the right connectors for servos.
FullOfBadIdeas:
My project has ample batteries and I need to drive two servos under load. Can I simply connect my servo control lead directly to power source, then servo control lead to my uno?I've seen servo drive shields and so forth, but rather avoid them if I don't need them.
It depends on what voltage your batteries are, and the working voltage of the servos..
If the servos are +5V, don't push them any higher than +6V battery!! If you have a 7.2V battery,
It's a very good idea to put a 7805 regulator between. (+7.2 to the input, common GND, +5V output to a common supply rail for the servos).. If you're talking a +12V battery, then by all means, you MUST put a regulator to bring it down, or you'll fry the H bridge inside the servo. Also, the 7805 should be heat-sinked as well.. (not mechanically critical, but a little silicone grease helps).
Thx guys - one more sub part to this since you brought up powering the boards too...
my batt is 12v. I am going to use a quality/built adjustable power regulator - so I can make the low side something like 3-8v.
my thoughts - make the low side 5.5 or 6v - so that I can power my uno, and also power the servos directly. I think the uno's range on input is like 3-9v?? servos about same range, but more torque at higher voltages.
No, the Uno's recommended range is 6-9v, depending on how you connect it. It would work fine on 6V applied to the Vin pin. The barrel jack requires a fractionally higher voltage.
MorganS:
No, the Uno's recommended range is 6-9v, depending on how you connect it. It would work fine on 6V applied to the Vin pin. The barrel jack requires a fractionally higher voltage.
The Vin & input from the barrel socket, are actually the same.. just linked by a foil trace.. It's the logic back to the ATMEGA328 chip, that has the limitations 3-5V..
And, actually, the regulator onboard (source: UNO R3 Schematic: NCP1117ST50T3G), from the Vin and connector, can go up as high as 20V, before you overload it. (though, just for safety, I keep a dual regulator pack handy.. a 7809 and a 7805 on a heatsink.. I usually wire the battery to the input of the 7809, run a power wire from the output pin to a barrel plug, and to the input of the 7805, then the output of the 7805 to anything needing a higher-amperage +5V. (servos, etc.)
thx guys - let me make sure though I am 100% straight - goal - common grounds and not to have the power sources on the Unos do any motor/servo work. I'd rather use barrel just for the fact more "durable" and pins hard to get to on my shielded board.
12v---->my regulator---6v--->servo power
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6V
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Uno1 --- Uno 2 (on barrel inputs)
Yep! that'll work fine! The method I mentioned above, with the 2X regulator pack, I usually wire the high voltage (+12V) to the input of the 7809, the output of the 9V regulator, feeds a common rail, for anything requiring it, as well as a pair of pin jumpers to a type-N Barrel Connector. This will provide power to the arduino mainly. Connected to the +9V rail, I'll connect the input of the 7805, and it's output will go to a common +5V rail, for servos, ultrasonic range finders, GPS receiver, etc..their outputs and the servo inputs can be driven directly from the arduinos without problem..
12V-----[7809]---+---[7805]---------->+5V rail
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GND-->V | V <--GND
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+-------------+-----> +9V rail
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+----> Arduino main socket or Vin
A 7805 can't drive two servos under load reliably (7805's are rated at 1A, two servos could be quite a bit more).
You ideally want a 3A+ switching converter from 12V down to 5 or 6 for the servos, the 7809 can
do the Arduino power jack OK though.
cool - all set, thx. I bought this little guy - 5A 
I've gotten a few things from these guys - lots of power/meter goodies.
MarkT:
A 7805 can't drive two servos under load reliably (7805's are rated at 1A, two servos could be quite a bit more).
You ideally want a 3A+ switching converter from 12V down to 5 or 6 for the servos, the 7809 can
do the Arduino power jack OK though.
I've never had any problems with even 3x Futaba S3003's (4x of which I've self-converted to Constant rotation), though usually a near-zero load. Even though Parallax (Sorry, competitor) has the same versions, 2x constant rotation, and as many as 1 more for a gripper claw for their 'B.O.E. Bot' design(viewable here), and all they use to reduce 6V to 5V, is a single 7805 w/a heatsink (located to the left of the 2 sockets for the servos, sockets for up to 4x).. Their newer version of the base frame, also has a custom shield board the Arduino can be plugged onto, with the same heat-sinked 7805 regulator. (Viewable here) (though, I'm not a fan of drawing the power to that regulator to through the Vin pin like this design does.) If you're trying to drive larger than standard hobby servos, yes, You're right. But I'm going by the design of standard RC Aircraft servo with only a 40-50 oz./in. torque. Worse case, you can actually double the amperage, by literally paralleling stacking several 78xx regulators together. (all same pins & tabs together) I seem to remember, somewhere else here in this forum, someone's idea to reduce the heat and failure of the on-board regulator of the Arduino, was to stack a 2nd one on top, and wiring all pins in parallel.
FullOfBadIdeas, Glad some of this helped! I know some of my notes get over-technical, but things are pretty simple.
Dropping from 6V to 5V is very different from dropping from 12V to 5V in terms of thermal dissipation.
If you use a 1A component at 2A and it works for you, I wouldn't boast about it, just wonder
how soon before it fails...
Paralleling voltage regulators is simply wrong, it doesn't work and can fail catastrophically.