Hi.
I've bought a HS-805BB servo from here: http://www.servocity.com/html/hitec_servos.html
here's the documentation: http://www.servocity.com/html/hs-805bb_mega_power.html
The servo is attached to a mechanical arm. It's supposed to move it. I'm supplying the power with 6v battery (4 x AAA batteries), but the motor doesn't lift the arm!
I know that the weight of the arm is not out of the capacity of the servo because one of my friends is using the exact same servo for lifting a much heavier arm, and his works just fine. Mine just fails to lift. I guess it's a supply issue.
Note: In the beginning right when I change the batteries, the servo works awesome and lifts the arm, but after a couple of minutes, it gets weak! And the batteries are not out because I can operate this thing for several hours and it works, but not properly. However I can't use more batteries because the documentation says that the limit is 6v.
So what should I do?
At 6 volts, that thing is pulling almost 1 amp of current (830 mA) under -zero- load. Four AAA alkaline batteries in series will only supply (at max, with a quality battery - you don't mention your battery brand, so I can't look up the datasheet for it) around 1200 mAh:
...and if you are using really crappy ones, it could be much less (250 mAh!). Also - you don't note what -kind- of AAA batteries you are using (so I assumed alkaline); so - for instance - if you were using NiCd or NiMH, which have a different chemistry - you wouldn't get 6 volts from 4 of them in series; you would only get about 4.8 volts.
Basically, I am saying a couple of things here:
- You haven't given us enough information to know for certain what the issue is.
- That said, most likely you need to switch to a battery cell with more capacity, likely a C or D cell (or parallel smaller cell packs together).
Also - if you are using rechargeable cells, you should use 5 of them in series, not 4, to get the required 6 volts (and in that case, you could possibly stick to using AA cells instead of AAA cells; or compromise with sub-C cells).
Finally - you don't mention how long you expect the servo to run, or what kind of load it will be under (stall current is not mentioned in the specs, but I bet its more than an amp or so); knowing this is important to size the battery properly...
I guess it's a supply issue.
Is your battery setup identical to your friends or different?
Hi,
I was testing the current draw from a sample of servos last night, none of them were 'giant' and none of the had a particularly high torque specification.
One of the servos was able to draw 1.5 Amps from four AA Batteries, its highly unlikely you will get this from AAA batteries, its possible from AA's but if your servo really is a giant, you would be much better of with RC Batteries such as the previously suggested D or C cells, look for '7.2 NIMH' there are lots out there. An even better if a little more expensive option is LIPO batteries, these are light, available in more sizes, hold more charge and deliver far more current.
So your options are -
Cheap and cheerful -
- Get some bigger batteries of the type you are currently using
More expensive, higher performance -
2) Get a dedicated hobby battery such as an 7.2 Volt Nimh pack designed for RC Cars - you will need a 5Volt or 6Volt regulator to get the battery voltage down to the servo voltage, there are lots available for around 10 dollars.
3) Get a dedicated LIPO hobby battery, 7.4 to 8.4 volts, also needs a regulator to get the voltage down, but uses the most uptodate battery technology with better performance than NIMH.
Options 2 and 3 require a hobby quality battery charger which also adds to the cost.
A final option is a bench top power supply.
If I get a chance over the next day or two I will post some results from running servos against various battery packs with a load applied.
In the meantime - http://rcarduino.blogspot.com/2012/04/servo-problems-with-arduino-part-1.html
Duane B
Hi thanks for the replies.
My friend is using chargeable batteries, but I'm just using AAA Alkaline batteries.
So I guess the conclusion would be that I simply have to change the batteries 
and the motor didn't function properly because of the insufficient current.
I apologize if I didn't provide enough info. However the issue looks resolved now.
Thanks for the answers again!