hi,
I am trying to run two servos simultaneously on breadboard while writing to it about +- 20 degrees / milliseconds from sensor feedback. I tried using 9V batteries with a lm7805 voltage regulator but failed and now trying to get 4 AAs working. I was wondering if there is any suggestions as to what power source should I use.
Thanks in advance,
20 degree / millisecond, that's nearly 3 full revolutions a second! Good luck finding a servo that can do that...
But even if you would do it slower with a normal hobby servo, they are power hungry. A SG90 may draw like 300mA on average but easily has power spikes of 1,5-2A. That's not something a 9V battery can do.
4x AA might, but if you keep them moving at full speed as you say, you will need a much beefer power source. Or grab an adapter (5V @ 5A or about) or switch to a decent battery pack like a Lipo. And if you want to run it for extended time, be sure to get a pretty large pack because they will drain it pretty quick.
What does "+- 20 degrees / milliseconds" actually mean to you. Please post the code that's doing this.
Anyway for normal use of SG90s 4 x NiMH rechargeable AAs (Eneloops etc) should be fine. They can provide more current than basic primary AAs. You'll also have a much better chance if you don't use a breadboard to connect the servos. Breadboards can't handle servo currents. Direct connection is much better.
BTW manufacturer spec for SG90 stall (peak) current is 650mA +/-80mA. Larger servos can get to 1.5-2A but not micros like SG90s.
Steve
@slipstick Then you never measured them 
septillion:
@slipstick Then you never measured them
I have measured startup peak currents and stall currents on quite a few servos including plenty of SG90s (genuine and clones). I've never yet seen more than ~500mA on SG90s. If you've measured 2A peaks on any micro servo then I would be interested to hear the details.
Steve
@slipstick DMM or scope? When I used the latter I saw peaks well over 500mA but they will of course not register on a DMM.
Don't say you can't mitigate them with some capacitance, but there is just so much you can smooth with extra capacity. But it boils down to how much movement you will make. But it that's really 20 degree per millisecond I doubt 500mA will be even close 
I don't have any practical way to measure short peaks except with the scope. I might do another check when I next have a few servos around to measure.
OTOH I don't really know what that "+- 20 degrees / milliseconds" means either, which is why I asked...but no answer yet.
Steve
Thanks, so the +- 20 is when I am using a PID, the refresh rate is 0.002 seconds and the PID will be added to the Servo value, so depending on the output of the sensor like altitude, the servo might turn a lot like 20degrees.
Servo signals are sent at 50Hz so basically can't change in less than 20 milliseconds. So sending different commands every 2 ms is a bit pointless. And what servos are you using that you think can travel 20 degrees in 2ms? A typical micro servo can do 20 degrees in about 40-50ms.
Steve
Hi,
What is the application?
What are the servos driving and h ow much load?
If the servos when at rest are opposing a torque then they will continue to draw current.
Tom... 
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