Electronics > Electronics

3.7 v lipoly powering micro servo? bad idea?

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bdeuell:
I would not recommend powering the servos from the microcontroller voltage regulator. You run the risk or damaging the regulator as well as causing all sorts of interference and dropout issues for the microcontroller. For your application i would recommend powering the servos directly from the battery, assuming the new servos are designed to work with the voltage range the battery provides.

I also would definitely not assume that you will not see the stall current. not only is that poor design practice (unless you have some other limiting control in place) it is definitely not "trying to stay on the safe side". especially as you admit you have no idea what torque to expect. Also the servo will draw the full stall current and likely more each time it starts to move from a stopped position (albeit for a very brief time interval).

.3 kg-cm (while not actually units of torque ... technically it should be in force and distance not mass and distance) is equivalent to saying that a 1 cm long horizontal arm with a .3 kg weight attached at one end and the servo attached to the other. Also equal to a 10 cm long arm with a .03 kg weight. I can't provide any guidance on the forces you should expect as you have provided no details on the mechanics.

you can assume the current draw increases approximately linearly with torque from the no load current (at zero torque) to the stall current (at stall torque).

dmehling:
That is really helpful.  I had no idea that the servo would probably reach stall current levels as soon as it starts turning. 

mklrobo:
 :) Hello!
Bdeuell give great advice. In reference to your concern of powering the
servos, Venfors do offer servo driver circuits, which may simplify some
of the issues you have. All the power goes through the servo controller,
the MCU is isolated, and programming feedback is offered in some servo
driver kits. I assume noise filtering is maintained through the servo controller,
as well as protection.
In reference to the power booster issue, those would be extra circuits and weight, Vs.
IC chips for voltage regulators, which have little weight and compact.  ;D ;D

mklrobo:
 :) Hello!
Also, insofaras you batteries, ServoCity is having a sale on batteries,
as expressed in the Miscellanous section, in this forum.

mklrobo:
 :) Hello!
Thinking through the whole design issue, and the questions/directions
in sight, maybe this would be an option;
Buy the microcontroller, servos, and accessories that you think you will need.
Buy a power supply that can deliver a main voltage, in which you break down
into subsystems with voltage regulators. (alot of seperate power supplies would work too)
Set up a test jig and fixture, to be able to look at the entire setup. You can begin
programming, then measuring the results you are looking for. If any problems come up,
you can deal with them accordingly. When all your projections are realized, and the
system is the way you want it, you can assemble the unit in the form in which it will
fit on your Kindle. What do you think?   :-\ :-\

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