can i power up logic and servos thru 5.4 V power supply?
which is better, to power up logic with battery and to have other power supply for servos or to power up all through 9V power supply?
The 9V is OK for the logic supply, but is generally not enough current for the servos.
I recommend either:
- Use anything between about 5.5 and 9V for the logic, and use a seperate (much bigger) battery for the servos.
- Use a battery of 5.5V or more and run everything from it.
Option 1 is better.
Pete
hmm, aren’t standard servo’s 7.2v ? I don’t know much about electronics but isn’t it bad for the servos to supply more than 7.2v ?
Yes, when I said “much bigger” I meant in current capacity, not voltage.
That is, to run the SSC-32, a small ordinary 9V battery probably runs it for quite a while. But the servos need much more current, so a higher-capacity battery is needed. This generally means a physically larger battery.
The voltage for the servos wants to be in the 6 to 8 range.
Pete
That is the rout I will take; a battery for the “brains” and a 7.5v battery for the servos.
You can use a 5.5vdc suply to power the servos and the SSC-32’s electronics. However the 5.5vdc supply needs to have sufficient current capabilities to provide current to the servos. An 18 servo hexapod can draw 6A peaks. If the 5.5vdc supply can only deliver 5 amps, the voltage will sag, and the SSC-32 will reset. This will lose any pulse offsets that were sent to it, and cause the servo pulses to stop being generated.
It is not a good idea to use 5vdc for servos if they are going to be under a reasonable load. The servos are designed for 6vdc operation. The difference in the delivered torque from 5vdc and 6vdc is significant. Servos are an analog device, with inherant tolerances built into the design. So it is common to see servos powered by 7.2vdc NiMH and 7.4vdc LiPo batteries. It is important to know the voltage delivered from a battery is not exactly the same as the rating. A 7.2vdc NiMH battery right off the charger will read around 9.25vdc. Withiin a few minutes of use it will settle down more closely to the rated voltage. I was told by a Hitec rep that 12vdc will always let the magic smoke out of the device. 
When powering servos at 7.2vdc it is important to keep the movements reasonably controlled. It’s not a good idea to go from point A to point B at maximum speed especially if a large mass is attached, such as a robot leg or arm. Because you are operating the servo above its rated voltage the motor and geartrain are being stressed. I recommend using a lower voltage if you are writing a control program from scratch, or designing your own electronics, because it is possible to make a mistake that cause the servos to move wildly at high speed, which can break gears.
For a source of high-current power to run servos and such off of AC, one option is to use the power supply from an old (obsolete) PC. A typical PC supply from say 10 years ago will give you 5V at around 20 amps(!), plus 12V at 3 to 5 amps. Your local PC repair guy should be willing to sell you one for cheap (he may require you to take the entire PC box, because it’s of little/no value to him!).
If you’re not loading the servos too heavily, the 5V might be perfect to get things going. NOTE that some of these supplies do not work unless there is a moderate load on the 12V output. You can use an appropriate power resistor for this, but for some folks the easiest thing is a 12V bulb from your car, such as a dome-light or turn signal or taillight bulb.
As a next step, many of these supplies have a voltage adjustment inside, which can be used to get at or near 6V. [WARNING!!! Do not fiddle around inside a supply like this if you don’t know what you’re doing!! You could cause some ‘magic smoke’ to come out of your ears.]
I am using a small PC-type supply to run my quad at the moment. I was able to adjust it for 6.1 V output to run the SSC-32 and servos - it works great!
Pete
Perhaps a little word of caution:
I don’t think most digital servos will accept anything above 6V without damage. The same holds for mini and micro servos.
Also when you want reliable and reproductive servo speed, I recommend a regulated power supply, that is in my case 7,2 V NiMH or 7,4 LiPo @ 10A
and a low drop voltage regulator @ 6V, 20Amps. To avoid noise from the servos, a separate small battery might be in order for the logic.
i’m using AC adaptor 5.5V (4.5W, 700mA) and it is not enough.
i’ve conected 4 servos and when moving voltage on VS1 drops to 4.2V
i guess i have to find AC adaptor with more amps and higher voltage
Ordinary ‘AC adapters’ are not very good for this purpose.
They are generally not regulated, and the voltage marked on them is (maybe) true only for a current that is 2/3 or 3/4 of the marked current.
Not only does their voltage ‘dip’ significantly under load, but when the load is light, they often are at a voltage that is much higher than their ratings - this can fry your electronics!
Pete
We have 6vdc 2amp regulated wall packs for $19.95.
lynxmotion.com/Product.aspx? … egoryID=46
Check it out.